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Title:
TUBE LUMINESCENT RETROFIT USING HIGH POWER LIGHT EMITTING DIODES
Document Type and Number:
WIPO Patent Application WO/2012/042460
Kind Code:
A1
Abstract:
The invention relates to a LED-based lamp having low glare and being capable of providing uniform source luminance while employing high-power LEDs. The lamp includes two LEDs disposed on a surface, a first diffusing arrangement configured to diffusively reflect light incident thereon and comprising at least a first part positioned between the two LEDs,and two re-directing structures. Each of there-directing structures corresponds to a different one of the two LEDs and is configured tore-direct at least a first portion of light emitted by the corresponding one of the two LEDs to be incident on the first part of the first diffusing arrangement.

Inventors:
VAN DER SIJDE, Arjen Gerben (Building 44, AE Eindhoven, NL-5656, NL)
HEEMSTRA, Tewe Hiepke (Building 44, AE Eindhoven, NL-5656, NL)
PFEFFER, Nicola Bettina (Building 44, AE Eindhoven, NL-5656, NL)
KONIJN, Frans Hubert (Building 44, AE Eindhoven, NL-5656, NL)
Application Number:
IB2011/054221
Publication Date:
April 05, 2012
Filing Date:
September 26, 2011
Export Citation:
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Assignee:
KONINKLIJKE PHILIPS ELECTRONICS N.V. (Groenewoudseweg 1, BA Eindhoven, NL-5621, NL)
VAN DER SIJDE, Arjen Gerben (Building 44, AE Eindhoven, NL-5656, NL)
HEEMSTRA, Tewe Hiepke (Building 44, AE Eindhoven, NL-5656, NL)
PFEFFER, Nicola Bettina (Building 44, AE Eindhoven, NL-5656, NL)
KONIJN, Frans Hubert (Building 44, AE Eindhoven, NL-5656, NL)
International Classes:
G02B17/08; F21K99/00; F21V7/00; G02B5/02
Foreign References:
US20060067079A12006-03-30
JP2007048883A2007-02-22
US20100220484A12010-09-02
US20060067640A12006-03-30
EP0945673A11999-09-29
Attorney, Agent or Firm:
VAN EEUWIJK, Alexander et al. (High Tech Campus, Building 44, AE Eindhoven, NL-5656, NL)
Download PDF:
Claims:
CLAIMS:

1. A lamp comprising:

two light emitting devices (LEDs) disposed on a surface;

a first diffusing arrangement configured to diffusively reflect light incident thereon and comprising at least a first part positioned between the two LEDs; and

- two re-directing structures, wherein each of the re -directing structures corresponds to a different one of the two LEDs and is configured to re-direct at least a first portion of light emitted by the corresponding one of the two LEDs to be incident on the first part of the first diffusing arrangement. 2. The lamp according to claim 1 , wherein each of the re-directing structures is further configured to re-direct a second portion of light emitted by the corresponding one of the two LEDs to not be incident on the first diffusing arrangement.

3. The lamp according to any one of the preceding claims, wherein:

- the first diffusing arrangement further comprises a second part,

each of the re-directing structures is further configured to re-direct a third portion of light emitted by the corresponding one of the two LEDs to be incident on the second part of the first diffusing arrangement so that, for each of the two LEDs, a projection of the re-directed first portion of light onto the surface and a projection of the re-directed third portion of light onto the surface form an angle between 0 degrees and 180 degrees.

4. The lamp according to any one of the preceding claims, wherein each of the re-directing structures is rotationally symmetric with an axis of symmetry of the re-directing structure coinciding with an axis of symmetry of a beam pattern of the corresponding one of the two LEDs.

5. The lamp according to any one of claims 1-4, wherein each of the two LEDs comprises a light emitting die and a dome disposed over the light emitting die and configured to seal the die, and wherein, for each of the two LEDs, the corresponding re-directing structure is disposed over the dome.

6. The lamp according to any one of claims 1-4, wherein each of the two LEDs comprises a light emitting die and, for each of the two LEDs, the corresponding re-directing structure is disposed immediately over the die.

7. The lamp according to any one of the preceding claims, further comprising a diffusing cover configured to diffusively transmit light incident thereon, wherein the first diffusing arrangement is configured to diffusively reflect the light incident thereon to be incident on the diffusing cover.

8. The lamp according to any one of the preceding claims, wherein each of the re-directing structures is configured to re-direct light by total internal reflection.

9. The lamp according to any one of the preceding claims, wherein the first diffusing arrangement comprises one or more plates disposed on the surface.

10. The lamp according to claim 9, wherein the one or more plates of the first diffusing arrangement comprise flat plates and, preferably, wherein each of the two LEDs is in thermal contact to a thermal interface surface having a high thermal conductivity to dissipate heat generated from the LED and wherein the thermal interface surfaces contacting the two LEDs are parallel to and at least partially in contact with the flat plates of the first diffusing arrangement.

11. The lamp according to any one of the preceding claims, wherein the distance between the two LEDs is greater than 1.5 times the optical height of the lamp, preferably 2 times the optical height of the lamp. 12. The lamp according to any one of the preceding claims, further comprising:

a third LED disposed on the surface in a line with the two LEDs; a second diffusing arrangement configured to diffusively reflect light incident thereon a comprising at least a first part positioned between the third LED and one of the two

LEDs which is closest to the third LED; and a third re -directing structure corresponding to the third LED and configured to re-direct at least a first portion of light emitted by the third LED to be incident on the first part of the second diffusing arrangement,

wherein the re-directing structure corresponding to the one of the two LEDs which is the closes to the third LED is further configured to re-direct a fourth portion of light emitted by the corresponding LED to be incident on the first part of the second diffusing arrangement.

13. The lamp according to any one of the preceding claims, wherein each of the re-directing structures comprises an inner surface and an outer surface and wherein, for each of the re-directing structures:

the inner surface is adapted to form a chamber, wherein the chamber is adapted to at least partially encompass the corresponding LED,

the inner surface is adapted to refract at least a first part of the first portion of light emitted by the corresponding LED to be incident on the outer surface,

the outer surface is adapted to reflect the first part of the first portion of light incident thereon by total internal reflection, and

the inner surface comprises a peak.

14. The lamp according to claim 13, wherein, for each of the re-directing structures, the inner surface is rotationally symmetric with an axis of symmetry of the inner surface adapted to coincide with an axis of symmetry of a beam pattern of the corresponding LED, or each of the re-directing structures is rotationally symmetric with an axis of symmetry of the re-directing structure adapted to coincide with the axis of symmetry of the beam pattern of the corresponding LED.

15. The lamp according to claim 14, wherein in a cross-section of each of the redirecting structures, the cross-section including the axis of symmetry of the beam pattern of the corresponding LED, the peak is at a point along the axis of symmetry of the beam pattern of the corresponding LED.

Description:
Tube luminescent retrofit using high power light emitting diodes

FIELD OF THE INVENTION

Embodiments of the present invention relate generally to the field of illumination systems, and, more specifically, to LED-based lamps for providing large area illumination.

BACKGROUND OF THE INVENTION

As the efficacy (measured in lumen per Watt) and the luminous flux

(measured in lumen) of light emitting diodes (LEDs) increases and prices go down, it is expected that LED illumination and LED based lamps soon will be serious alternatives to and at a competitive level with until now predominant tube luminescent (TL) based lamps for providing large-area illumination. Such lamps are typically found in office buildings with form factors of 15 centimeter- to 2.4 meter-long tubes, having diameters 5/8 inch, 1 inch, 1.25 inch or even larger, providing uniform luminance along the length of the tube. A typical TL luminous flux output density is 3000 lumen per meter tube length. For LED retrofit, also lower values may be found.

Current LED lamps attempting to replace TL lamps are mostly fabricated by placing a large number of relatively low-power (e.g., 6 lumen) LEDs under a mildly diffusing cover. One such lamp is illustrated in Figures 1 A and IB, where Figure 1A presents a top view of a lamp 100 and Figure IB presents a side view. As shown, the lamp 100 includes a large number of low-power LEDs 110 arranged in two rows on a substrate 120. A typical distance between the LEDs 110 in a single row is 7 millimeters (mm), resulting in the effective distance between the LEDs 110 of 3.5 mm (such a distance is commonly referred to as "pitch"). Each of the LEDs 110 generates light mainly in the upward direction, as shown in Figure IB with arrows 130, towards a mildly diffusing cover 140 (shown with a dashed line).

One drawback of such an arrangement is that a large number of low-power LEDs placed relatively close to one another must be used in order to obtain sufficient luminous flux with acceptable uniform luminance (i.e., there are no visible dark and light spots along the tube). Employing high-power LEDs (e.g. 65 lumen or more) would allow obtaining similar luminous flux while placing LEDs further apart from one another, thereby decreasing the cost of the LED-based lamps and making them more competitive with TL lamps.

However, using just a linear array of high-power LEDs does not allow obtaining a light source with uniform luminance. Two uniformity related phenomena should be considered. First phenomenon is that the directed strong light produced by each high- power LED will show spots on the diffusing cover (here to be addressed as "spot non- uniformity"). Second phenomenon is that, depending on diffuser properties, a smaller or larger part of the light might go substantially undif fused through the cover, showing the source as a small bright spot (an extreme case of "glare non-uniformity"). Depending on the resulting luminance of this spot and the exposure time, it might lead to unpleasant afterimages or even eye damage. Using a cover that can diffuse light more strongly could alleviate the glare and spot non-uniformity problems to a certain extent, but at the expense of more (lossy) reflections within the system, and, thus, reduced efficacy of the lamp.

What is needed in the art is a solution that can improve on at least some of the problems described above.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a LED-based lamp having low glare and being capable of providing uniform source luminance while employing high-power LEDs.

According to one aspect of the invention, a lamp is disclosed. The lamp includes two LEDs disposed on a surface and a first diffusing arrangement configured to diffusively reflect light incident thereon. The first diffusing arrangement includes at least a first part positioned between the two LEDs. The lamp also includes two re-directing structures, where each of the re-directing structures corresponds to a different one of the two LEDs and is configured to re-direct at least a first portion of light emitted by the

corresponding one of the two LEDs to be incident on the first part of the first diffusing arrangement.

As used herein, the phrase "a first part of the diffusing arrangement is positioned between the two LEDs" and derivatives thereof are intended to describe the fact that the first part of the diffusing arrangement is symmetric with respect to a plane that includes the line connecting [the centers of] the two LEDs on the surface on which the LEDs are disposed and is perpendicular to the surface on which the LEDs are disposed. In the following, such plane of symmetry is referred to as a "longitudinal symmetry plane." For example, the "first part positioned between the two LEDs" defined in this manner could be e.g. a flat diffusing reflector plate that is disposed on or parallel to the surface on which the LEDs are placed and is symmetric with respect to the longitudinal symmetry plane (e.g. sandglass arrangements described in Figs. 3A through 6B).

Embodiments of the present invention are, in part, based on the recognition that by placing a diffusing reflector in between two LEDs and by re-directing the light emitted by the two LEDs to be incident on such a diffusing reflector allows obtaining uniform luminance between the LEDs. Designing the re-directing structures in such a manner that they would re -direct light emitted by the LEDs to be incident on the diffusing reflector not only close to the LEDs but also further away from the LEDs allows spacing the LEDs further apart from one another while still maintaining adequate luminance uniformity. In turn, employing high-power LEDs while spacing the LEDs further apart allows the lamp to provide illumination of specific illumination intensity from a specific, (lower) luminance (by emitting from a larger area) while using less LEDs, relative to prior art implementations. As a result, a LED-based lamp having low glare and being capable of providing uniform source luminance while having high efficiency and limited diameter (for tube lamps) or thickness (for area lamps) may be provided.

In an embodiment, each of the re-directing structures is further configured to guide a second portion of light emitted by the corresponding each of the two LEDs to not be incident on the first diffusing arrangement. This embodiment provides that some of the light emitted by the LEDs may "leak out" from the re-directing structure without being diffusively reflected by the first diffusing arrangement. In one embodiment, such "leaked out" light could comprise 5-10% of the total light emitted by the LEDs, however, this percentage may be further adjusted in order to obtain sufficient uniform lit appearance of the lamp. For maximal efficiency, this percentage should be as low as possible. However, for minimized spot-non-uniformity, the amount of leaked-out light should be proportional to the length of the cover on which it effectively arrives. Then, the amount of lumen per unit length of the tube for the leaked-out light and for the light diffused by the diffusing reflector should preferably be identical.

Positions and shapes where the light leaks out (e.g., top center of the redirecting structure of each LED, the corners of the re -directing structure of each LED, etc.) and the amount and direction of the leaked light rays may also be optimized in terms of the uniform source luminance. For a purely refractive re-directing structure, this can be done by adding carefully calculated corrugations (e.g. microstructures like micro -lenses, 'holographic diffuser' -like structures or other microstructures with a defined angular distribution) to selected positions of the outer surface of the re-directing structure. If the outer surface of the re-directing structure is a mirror, similar structures could be added but, in addition to that, the mirror can be locally made more or less transparent to get the desired kind of leakage.

Alternatively or additionally, controlled light leakage may be achieved by introducing one or more concentric rings on the inner surface and/or the outer surface of the re -directing structure and/or extending between the inner surface and the outer surface. When the redirecting structure is rotationally symmetric, the center of the concentric rings may be adapted to coincide with an axis of symmetry of the re -directing structure. Such rings could allow easier modification of the optics. Therefore, the symmetry of the rings is preferably linked to the symmetry of the optics (i.e., the re-directing structure) and/or the lamp incorporating such optics rather than to the symmetry of the corresponding LED. Of course, in other embodiments, the rings could be made symmetric with respect to the axis of symmetry of the beam pattern of the corresponding LED.

Furthermore, there may be an extra volume diffuser and/or surface diffuser present between the cover and the re-directing structure, to improve the uniformity still further. The extra volume and/or surface diffuser may have an optimized shape and/or optical properties that vary over its volume or surface, respectively. If the re-directing structure is transparent, it may also contain scattering elements in the bulk or on the surface to induce light leakage.

In an embodiment targeted for best spot uniformity, the second portion may include less than 45 % of the light emitted by each of the two LEDs. This embodiment advantageously specifies that most of the light emitted by the LEDs (55% or more) can be diffused, with a fraction of the light being "leaked out" from the re-direction structure about equal to the ratio of the length of the re -direction structure to the length of the LED pitch.

In an embodiment targeted for best efficiency but not for best spot uniformity, the second portion may include less than 5-10 % of the light emitted by each of the two LEDs. This embodiment advantageously specifies that most of the light emitted by the LEDs (90% or more) can be diffused with only a small fraction of the light being "leaked out" from the re-direction structure.

In an embodiment, the first diffusing arrangement may further include a second part and each of the re -directing structures may be further configured to re-direct a third portion of light emitted by the corresponding one of the two LEDs to be incident on the second part of the first diffusing arrangement so that, for each of the two LEDs, a projection of the re-directed first portion of light onto the surface and a projection of the re-directed third portion of light onto the surface form an angle between 0 degrees and 180 degrees. This embodiment specifies that some of the light emitted by the LEDs may be re -directed not along the line connecting the two LEDs, but at an angle to that line (i.e., to the "sides" of the LEDs). This may be particularly advantageous for obtaining uniform illumination from lamps including four or more LEDs arranged in a rectangular pattern, all of the LEDs thereby together forming an areal light source.

In an embodiment, each of the re-directing structures may be rotationally symmetric with an axis of symmetry of the re-directing structure coinciding with an axis of symmetry of a beam pattern of the corresponding one of the two LEDs.

As used herein, the term "rotationally symmetric structure" refers to a structure having symmetry with respect to rotations to certain or all angles around an axis of symmetry of the structure. In one embodiment, each of the re-directing structures may be rotationally symmetric with respect to rotations of all angles around the axis of symmetry of the structure, thus, having a circular top profile. In another embodiment, each of the redirecting structures may be rotationally symmetric with respect to rotations of only particular angles around the axis of symmetry of the structure, thus, having a non-circular but symmetric top profile. For example, a re-directing structure which has rotational symmetry with respect to rotations of 90 degrees may have a square top profile.

Further, as used herein the term "beam pattern" of a LED refers to the intensity distribution of the LED which gives the flux per solid angle in all direction of space.

In an embodiment, each of the two LEDs may include a light emitting die and a dome disposed over the light emitting die and configured to seal the die, where, for each of the two LEDs, the corresponding re-directing structure is disposed over the dome. This embodiment specifies that the re-directing structures may be included as "secondary optics," where, as used herein, this term refers to optical elements not included within a LED package. By contrast, the term "primary optics" typically refers to elements included within a LED package such as a light emitting die, a dome disposed over the die and configured to protect the die, a high reflecting surface onto which the die is mounted, etc.

In an embodiment, each of the two LEDs may include a light emitting die and, for each of the two LEDs, the corresponding re-directing structure may be disposed immediately over the die. In contrast to the previous embodiment, this embodiment provides that the re-directing structures may be included as "primary optics" in a LED package. In yet other embodiments, each of the two LEDs may include a number of light emitting dies having either the dome disposed over them or directly the re-directing structure.

In an embodiment, the lamp may further include a diffusing cover configured to diffusively transmit light incident thereon, where the first diffusing arrangement may be configured to diffusively reflect the light incident thereon to be incident on the diffusing cover. This embodiment provides for additional diffusion by a diffusively transmitting cover. In a preferred embodiment, each beam of the first portion of light emitted by each of the LEDs is diffusively reflected only once by the first diffusing arrangement before either being directly transmitted out of the lamp or being diffusively transmitted out of the lamp via the cover. The light being reflected in this manner allows keeping light losses to a minimum.

In an embodiment, each of the re-directing structures may be configured to redirect light by total internal reflection. In contrast to some prior art implementations which re-direct light with mirrors, this embodiment provides the advantage of the re-directing structure having minimal losses in guiding the light emitted by the LEDs.

In an embodiment, the first diffusing arrangement may include one or more plates disposed on the surface on which the LEDs are disposed. This embodiment ensures that the light emitted by the LEDs is re-directed "backwards" with respect to the direction in which the light is emitted before being diffused by the diffusing reflector, as opposed to being directed "upwards" towards diffusively transmitting cover as was done in prior art systems such as e.g. in the arrangement illustrated in Fig. IB. In one embodiment, as much as 90-95% of all of the light emitted by the LEDs may be re-directed backwards. In one embodiment, the first part of the first diffusing arrangement is positioned on the surface on which the LEDs are disposed, along a line connecting the two LEDs.

In an embodiment, the one or more plates of the first diffusing arrangement may include flat plates. This embodiment provides the advantage that the first diffusing arrangement may be fabricated starting from a flat sheet of diffusively reflecting material by cutting and bending operations only, resulting in a relatively simple manufacturing process. Preferably, the first diffusing arrangement would be fabricated from an optically low-loss material (i.e., the material capable of reflecting most of the light incident thereon with only a minor portion of the light being lost due to absorption).

In an embodiment, each of the two LEDs may be in close thermal contact to a thermal interface surface having a high thermal conductivity to dissipate heat generated from the LED, where the thermal interface surfaces contacting the two LEDs may be parallel to and at least partially in contact with the flat plates of the first diffusing arrangement. The first diffusing arrangement may also be fabricated, at least partially, from a material having a high thermal conductivity. This embodiment provides an advantage of using the first diffusing arrangement for spreading the heat from the LEDs.

In an embodiment, each of the two LEDs may include a high-power LED capable of emitting light with luminous flux of 65 or more lumen. Including high-power LEDs in a lamp allows using less LEDs to obtain the desired luminance output from the lamp, thereby decreasing the cost and the complexity of the lamp. In addition, since high- power LED dies capable of emitting such fluxes usually have sizes larger than lxl mm , including re-directing structures where the inner surfaces are modified to include a peak is particularly advantageous for such LEDs. However, while the embodiments disclosed herein may be especially beneficial for using high-power LEDs, of course, the teachings of the present invention could also be implemented with LEDs having luminous flux of less than 65 lumen.

In an embodiment, the distance between the two LEDs may be greater than 1.5 times the height of the "optical height" of the lamp, preferably 2 times the "optical height of the lamp." As used herein, the term "optical height of the lamp" refers to the shortest distance height within the lamp reserved to transmit the light from the LED to outside of the lamp (and does not include e.g. light blocking heatsinks). Being able to position LEDs at such distances from one another while still maintaining adequate uniform source luminance provided by the lamp also allows using less LEDs, relative to prior art implementations, thereby also decreasing cost and complexity of the lamp.

In an embodiment, the lamp may further include (i) a third LED disposed on the surface in a line with the other two LEDs, (ii) a second diffusing arrangement configured to diffusively reflect light incident thereon and including at least a first part positioned between the third LED and one of the two LEDs which is closest to the third LED, and (iii) a third re-directing structure corresponding to the third LED and configured to re-direct at least a first portion of light emitted by the third LED to be incident on the first part of the second diffusing arrangement. The re-directing structure corresponding to the one of the two LEDs which is the closest to the third LED may be further configured to re-direct a fourth portion of light emitted by the corresponding LED to be incident on the first part of the second diffusing arrangement. Such an embodiment provides a lamp in which three LEDs are arranged in a line, preferably a straight line. Placing a diffusing arrangement between each pair of LEDs, designing the re-directing structure of the LED that is in between the other two LEDs to re -direct light emitted by that LED onto both diffusing arrangements adjacent to that LED (preferably, in equal portions), and designing the re-directing structures of the other two LEDs to re -direct light emitted by each of the other two LEDs onto the adjacent diffusing arrangement enables the light emitted by the three LEDs to be uniformly distributed along the length of the lamp. The three LEDs, combined, may then perform as a linear light source. Similar reasoning applies for any higher number of LEDs included in the lamp.

In an embodiment, each of the re-directing structures may comprise an inner surface and an outer surface such that, for each of the re-directing structures, the inner surface is adapted to form a chamber, where the chamber is adapted to at least partially encompass the corresponding LED, the inner surface is adapted to refract at least a first part of the first portion of light emitted by the corresponding LED to be incident on the outer surface (before being incident on the first part of the first diffusing arrangement), the outer surface is adapted to reflect the first part of the first portion of light incident thereon by total internal reflection, and the inner surface comprises a peak. The peak may be considered to be formed by two portions of the inner surface and would preferably be adapted to be above the center of the corresponding LED. In various embodiments, in a cross-sectional view of a redirecting structure, the cross-section being taken so as to include an axis of symmetry of the beam pattern of the corresponding LED, the two portions could comprise e.g. two linear portions of the inner surface joining at an angle (i.e., the two linear portions form an angle less than 180 degrees), two convex curves, two concave curves, or any combination of each of the two portions being a linear portion, a convex curve, or a concave curve, where, optionally, the peak may further be rounded. In some embodiments, the peak may be considered to be a "head" of the inner surface of the re -directing structure while the portions of the inner surface next to the peak could be considered to be the "shoulders." However, in other embodiments, the peak may be considered to be a "head" of the inner surface without having any "shoulders" in the inner surface of the re-directing structure.

As used herein, the inventive concept of an inner surface of a re-directing structure comprising a peak is intended to cover all embodiments where the inner surface is adapted to form a chamber, around a LED, which chamber has aspherical, generally convex shape. The term "generally convex" is used to describe a shape that, while it may include some concave or linear portions, is, in general, convex, such as e.g. the inner surfaces shown in Fig. 18. In line with these definitions, the concept of the inner surface comprising a peak does not cover the inner surface forming a dome-shaped chamber (because dome is spherical, not aspherical) and does not cover the inner surface forming a rectangular chamber with the LED adapted to be disposed along a side of the rectangle (because the rectangle is not "generally convex").

Such a re-directing structure could be used to re-direct the light emitted by the corresponding LED from substantially vertical direction to substantially horizontal or downward horizontal ("backwards") direction. Such a structure could also be used as an incoupling structure adapted to couple light emitted by the corresponding LED into a light guide, in which case the re-directing structure could be an integral part of the light guide.

The idea of the inner surface of a re -directing structure having a peak is based on the recognition that, when thickness of the re-directing structure is reduced to the point that the size of the LED's emitting surface is comparable with the thickness of the redirecting structure, the LED may no longer be considered to be a point light source emitting light from a single point at the center of the emitting surface. Instead, particular attention must be given to the extended size of the LED's emitting surface when determining the shape of the re-directing structure that would allow all light beams emitted by the LED and incident on the outer surface to be reflected by TIR. When such attention is not given, light beams emitted from near the edges of the LED's emitting surface could enter the re-directing structure at such an angle that a TIR condition at the outer surface of the re-directing structure is not satisfied and these light beams will escape, or leak out from, the re-directing structure. Therefore, care should be taken to ensure that light beams emitted from near the edges of the LED's emitting surface are incident on the outer surface of the re -directing structure in a manner that the TIR condition would still be satisfied. Without increasing the overall thickness of the re-directing structure, such care includes adapting the shape of the inner surface with respect to the maximum thickness of the re-directing structure and the shape of the outer surface of the re-directing structure so that all of the light beams emitted by the LED and incident on the inner surface, even the light beams emitted from near the edges of the LED's emitting surface, could be refracted by the inner surface at such angles that the angles of incidence of the refracted light beams on the outer surface of the LED would satisfy the TIR condition. Only then can substantially all of the light beams emitted by the LED be contained in the re-directing structure.

A dome-shaped inner surface used in the prior art implementations, described below and illustrated in Fig. 7, is not optimal in terms of the minimized light leakage because some of the light beams emitted from near the edges of the LED may leak out from the outer surface of the re -directing structure, as shown in Figs. 15B and 15D and explained in greater detail below. By contrast, an inner surface according to the embodiments of the present invention including a peak above the LED is more optimal because only for such not-dome- shaped surfaces a shape could be determined, with respect to the shape of the outer surface and the maximum thickness of the structure, so that all of the light beams emitted by the LED would be refracted by the inner surface at such angles that the angles of incidence of the refracted light beams on the outer surface of the re-direction structure would satisfy the TIR condition.

In an embodiment, for each of the re-directing structures, not the entire redirecting structure but only the inner surface of the re-directing structure may be rotationally symmetric with an axis of symmetry of the inner surface adapted to coincide with an axis of symmetry of a beam pattern of the corresponding LED (i.e., the chamber adapted to encompass the LED may be made rotationally symmetric) and vice versa.

In an embodiment, in a cross-section of each of the re-directing structures, the cross-section including the axis of symmetry of the beam pattern of the corresponding LED, the peak is at a point along the axis of symmetry of the beam pattern of the corresponding LED. Thus, the inner surface of each re -directing structure would include a single peak above the corresponding LED, along the axis of symmetry of the beam pattern of the LED.

Hereinafter, an embodiment of the invention will be described in further detail. It should be appreciated, however, that this embodiment may not be construed as limiting the scope of protection for the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In all figures, the dimensions as sketched are for illustration only and do not reflect the true dimensions or ratios. All figures are schematic and not to scale. In particular the thicknesses are exaggerated in relation to the other dimensions. In addition, details such as LED chip, wires, substrate, housing, etc. have sometimes been omitted from the drawings for clarity.

Fig. 1 A illustrates a top view of an LED-based lamp according to prior art; Fig. IB illustrates a cross- sectional side view of the LED-based lamp of

Fig. 1A;

Fig. 2A illustrates a LED-based lamp, according to one embodiment of the present invention; and

Fig. 2B illustrates a cross- sectional side view of the LED-based lamp of

Fig. 2A; Fig. 2C illustrates a LED-based lamp, according to another embodiment of the present invention;

Fig. 3A illustrates a three-dimensional view of a LED arrangement, according to one embodiment of the present invention;

Figs. 3B and 3C illustrate cross-sectional side views, in different scales, of the

LED arrangement of Fig. 3A;

Fig. 4A illustrates a three-dimensional view of a LED arrangement with upward leakage, according to one embodiment of the present invention;

Fig. 4B illustrates a cross- sectional side view of the LED arrangement of Fig. 4A;

Fig. 5A illustrates a three-dimensional view of a LED arrangement with upward leakage, according to another embodiment of the present invention;

Fig. 5B illustrates a cross- sectional side view of the LED arrangement of

Fig. 5A;

Fig. 6 A illustrates a three-dimensional view of a rotationally symmetric LED arrangement, according to one embodiment of the present invention;

Fig. 6B illustrates a cross- sectional side view of the LED arrangement of

Fig. 6A;

Fig. 7 illustrates a light guide according to prior art;

Fig. 8A illustrates a three-dimensional view of a LED arrangement with an optimized inner surface of a re-directing structure, according to an embodiment of the present invention;

Fig. 8B illustrates a cross- sectional side view of the LED arrangement of Fig. 8A, according to one embodiment of the present invention;

Fig. 8C illustrates a cross- sectional side view for a light guide incoupling application of the LED arrangement of Fig. 8A, according to another embodiment of the present invention;

Fig. 9 provides a schematic illustration of a LED arrangement used in the description of Figs. 10-14;

Fig. 10 provides a computation result for a cross-sectional shape of the outer surface of a re-directing structure satisfying the TIR condition when the LED is considered to be a point source emitter; Fig. 11 provides a computation result for a cross-sectional shape of the outer surface of a re-directing structure satisfying the TIR condition when the LED is considered to be an immersed extended source emitter;

Fig. 12 illustrates dependence of the optics size on the size of the emitting surface of the LED for the above-described re-direction structures satisfying the TIR condition;

Fig. 13 provides a comparison of the computation results for a cross-sectional shape of the outer surface of a re-directing structure satisfying the TIR condition when the LED is considered to be a point source emitter, or an immersed extended source or an extended source encompassed by a dome-shaped inner surface of the re -directing structure;

Fig. 14 provides a comparison of the computation results for the different cross-sections of the minimum thickness TIR re-directing structures with different incoupling chambers;

Figs. 15A-15D illustrate differences with respect to light leakage between a re- directing structure forming a dome chamber around a LED and a re-directing structure according to an embodiment of the present invention forming a chamber having a sharp peak above the LED;

Fig. 16 illustrates a cross-sectional side view in the plane 850 of a LED arrangement with controlled light leakage, according to one embodiment of the present invention;

Fig. 17 illustrates a cross-sectional side view in the plane 850 of an LED arrangement with controlled light leakage, according to another embodiment of the present invention; and

Fig. 18 illustrates inner surfaces comprising peaks of different shapes, according to various embodiments of the present invention.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth to provide a more thorough understanding of the present invention. However, it will be apparent to one of skill in the art that the present invention may be practiced without one or more of these specific details. In other instances, well-known features have not been described in order to avoid obscuring the present invention.

Fig. 2A illustrates a top view of a portion of a LED-based lamp 200, according to one embodiment of the present invention. As shown, the lamp 200 includes at least two LEDs 210 disposed on a surface 220. Each of the LEDs 210 is encompassed by a re-directing structure 230. Fig. 2A also illustrates a diffusing arrangement 240. In this two-dimensional drawing, the diffusing arrangement 240 may be said to be symmetrical with respect to a line 250 connecting the centers of the LEDs 210. In a three-dimensional view of the lamp 200, the diffusing arrangement 240 would be symmetrical with respect to a plane that is perpendicular to the surface 220 and that includes the line 250 (i.e., the longitudinal symmetry plane).

Fig. 2B illustrates a cross- sectional side view of the lamp 200, the cross- section taken along the longitudinal symmetry plane.

In operation, each of the two LEDs 210 emit light (either as a top-emitter LED or a side-emitter LED) which is incident on the corresponding re-directing structure 230 (illustrated in greater detail in subsequent Figures). The re -directing structures 230 then guide the light to be incident onto the diffusing arrangement 240. Fig. 2B schematically illustrates the light being incident onto the diffusing arrangement 240 at points 261, 262, 263, and 264. The diffusing arrangement 240 is configured to diffusively reflect the light incident thereon, as shown with arrows originating from the points 261-264. To that end, in one embodiment, the diffusing arrangement 240 may comprise a flat white surface disposed over the surface 220 and comprised e.g. of white plastic, white paint or the like. Note that the diffusing arrangement 240 may not be drawn to scale. In general, the amount of light not hitting the diffusing arrangement and simultaneously not hitting the cover, should be minimized in order to maximize the efficacy. In other embodiments, the diffusing arrangement may be comprised of a plane sheet having folded side- wings that extend to the cover (e.g. to the cover 270 described below).

As is shown in Fig. 2B, the re-directing structures 230 guide the light emitted by the LEDs 210 backwards with respect to a plane covering the re-directing structures 230 on top and being "horizontal" or parallel to the surface 220, shown in Fig. 2B with a line 276 (i.e., the angles between the plane 276 and the rays of the re-directed light incident on the diffusing arrangement 240 are greater than zero degrees and less than 90 degrees as measured from the plane 276 in a clockwise direction). This contrasts prior art implementations where the light may be guided either upwards or parallel to such a plane 276.

Each of the LEDs 210 may comprise high-power LEDs, capable of providing light with luminous output of 65 or more lumen. Because the re-directing structures 230 are configured to guide the light emitted by the LEDs 210 to be incident on the diffusing arrangement 240 between the LEDs 210 and because the re-directing structures 230 may be designed so that the light is incident on the diffusing arrangement 240 not only close to the LEDs 210 (points 261, 264), but also relatively far away from the LEDs 210 (points 262, 263), uniform illumination may be obtained along the longitudinal direction of the lamp 200 (i.e., along the line 250) while disposing the LEDs 210 relatively far away from one another. In one embodiment, the distance between the LEDs 210 may be between 5 cm and 12 cm.

In order to minimize light losses, the re-directing structures 230 and the diffusing arrangement 240 are designed in such a way that the light is preferably only reflected once by the diffusing arrangement 240 before escaping the lamp 200 or before being incident on an optional cover 270, shown in Fig. 2B. In order to approach this optimum as much as possible, the re-directing structure should have a beam pattern of which the largest possible fraction hits the diffusing arrangement. In one embodiment, the cover 270 may comprise a transparent material so that the cover 270 simply transmits the light incident thereon. Alternatively, the cover 270 may comprise a diffusively transmitting layer, configured to diffusively transmit the light incident thereon, thereby further improving the uniformity of the illumination provided by the lamp.

As used herein, the term "diffusively reflect" and the derivatives thereof refer to more than 80-90% of light being quasi-Lambertian reflected and the term "diffusively transmit" and the derivatives thereof refer to more than 40-60% of light being quasi- Lambertian transmitted. Preferably, the diffusive properties of the cover 270 should be optimized to maximize the amount of transmitted light while still fulfilling the uniformity requirements.

In other embodiments, the lamp 200 may, optionally, include any number of LEDs 210 larger than two disposed along the line 250. This is indicated by lines 272 and 274 on the ends of the portion of the lamp 200 shown in Figs. 2A and 2B. In such embodiments, each LED 210 would be encompassed by a corresponding re-directing structure 230, as shown in Fig. 2C with an exemplary LED-based lamp 280 having four LEDs 210. All of the discussions above with respect to Figs. 2A and 2B are applicable here with minor adjustments that a person skilled in the art would be able to recognize and, therefore, in the interest of brevity, are not repeated here. In the lamp 280, the re-directing structure 230 of each of the LEDs 210 is configured to guide the light generated by corresponding LED 210 to be incident onto the diffusing arrangements 240 adjacent to the particular LED 210 (same also holds for the lamp 200). Thus, for the exemplary architecture of the lamp 280, the redirecting structure 230 of the left-most LED 210 is configured to re-direct the light emitted by the left-most LED 210 to be incident onto the diffusing arrangement 240 provided on the left side of the left-most LED 210 and to be incident onto the closest one of the diffusing arrangements 240 provided on the right side of the left-most LED 210. Similarly, for the LED 210 disposed closest to the left- most LED 210, the corresponding re-directing structure 230 of that LED is configured to re-direct light emitted by that LED to be incident onto the closest one of the diffusing arrangements 240 provided on the left side of that LED and onto the closest one of the diffusing arrangements 240 provided on the right side of that LED, and so on. In this manner, the lamps 200 and 280 may act as linear light sources capable of providing uniform illumination along the longitudinal direction (i.e., the line 250) of the lamps.

Various embodiments of how a portion 290 of the lamp 280 (or the analogous portion of the lamp 200) may be designed are described below with reference to Figs. 3A-6B. The lamp 280 includes four such portions 290. The lamp 200 includes two analogous portions.

Fig. 3 A illustrates a three-dimensional view of a LED arrangement 300, according to one embodiment of the present invention. The LED arrangement 300 may be used as the portion 290 in the lamp 280. In the following, the term "LED arrangement" is used to describe an optical arrangement including a LED, a corresponding re-directing structure and, optionally, portions of the diffusing arrangements adjacent to the LED within the lamp 280. Thus, each of the LED arrangements described with respect to Figs. 3A-6B are illustrated in the corresponding figures to include the portions of the diffusing arrangements adjacent to the LED, while each of the LED arrangements described with respect to Figs. 8A- 18 are illustrated without the portions of the diffusing arrangements adjacent to the LED, even though a person skilled in the art that the description of Figs. 8 A- 18 applies equally to the LED arrangements including the portions of the diffusing arrangements adjacent to the corresponding LED.

As shown in Fig. 3A, the LED arrangement 300 includes a LED 310

(analogous to the LED 210 of the portion 290). In the embodiment illustrated in Fig. 3A, the LED 310 includes a LED die 312 covered with a dome 314. The LED die 312 is configured to emit light in response to a drive signal. Material used as the LED die 312 primarily determines characteristics of the LED 310, such as e.g. color, brightness, and/or intensity of light. Possible materials that could be used for the LED die 312 include inorganic semiconductors, such as e.g. GaN, InGaN, GaAs, AlGaAs, or organic semiconductors, such as e.g. small-molecule semiconductors based on Alq 3 or polymer semiconductors based e.g. on the derivatives of poly(p-phenylene vinylene) and polyfluorene.

The dome 314 is usually configured to e.g. protect the LED 312 from the environmental factors and/or determine characteristics of the LED such as e.g. maximizing the total luminous flux of the LED while still fitting within a certain envelope or matching the intensity profile of the LED for the largest number of applications. In various embodiments, the dome 314 may actually have a different shape than the half-dome illustrated in Fig. 3A, suitable for particular requirements for applications of the LED 310.

The LED arrangement 300 also includes diffusing reflectors 320 and 322 (analogous to the two diffusing arrangements 240 of the portion 290, one diffusing arrangement 240 on one side of the LED 210 and the other diffusing arrangement 240 on the other side of the LED 210), each of which is designed to diffusively reflect the light incident thereon.

The LED arrangement 300 further includes a re-directing structure 330 (analogous to the re -directing structure 230 of the portion 290) encompassing the LED 310 and having a shape that resembles a portion of a sandglass. Because of such shape, the LED arrangement 300 may also be referred to herein as the "sandglass arrangement 300." The redirecting structure 330 is a lens designed to change the path of light emitted by the LED 312 to be incident on the diffusing reflectors 320 and 322 mainly along the longitudinal direction (shown with arrows 342 and 344) of a lamp in which the LED arrangement 300 would be incorporated (such as e.g., the lamp 200 or the lamp 280). In a preferred embodiment, the redirecting structure 330 may be fabricated from a material that does not absorb light emitted by the LED die 312 and is designed to guide the light emitted by the LED die 312 based on the total internal reflection principle. For example, the re-directing structure 320 may be fabricated from transparent PMMA, polycarbonate, glass, or comparable materials. In other embodiments, the re-directing structure 320 could also be implemented with mirror surfaces (e.g. metallic or dielectric), either hollow or filled with transparent material.

As shown in Fig. 3A, a plane 350 is a plane of symmetry for the diffusing reflectors 320, 322, the re -directing structure 330, and the LED 310. Because this plane lies along the longitudinal directions shown with arrows 342 and 344, plane 350 is the longitudinal symmetry plane.

Fig. 3B illustrates a cross- sectional side view in the plane 350 of the LED arrangement 300 shown in Fig. 3A. In Fig. 3B, elements with the same reference numbers as in Fig. 3A illustrate the same elements as in the Fig. 3A. As shown in Fig. 3B with a gap 335, in the illustrated embodiment, the redirecting structure 330 encompasses the LED 310 without being in physical contact with the LED 310. Thus, the gap 335 is the gap between the dome 314 of the LED 310 and the redirecting structure 330. The gap 335 may be air or may be filled with a material having suitable optical properties, such as a lower index of refraction than the re-directing structure. In the latter case, this may require a different shape of the redirecting structure. In an alternative embodiment, the re-directing structure may also be in physical contact with the LED 310.

As shown in Fig. 3B, in operation, the LED die 312 emits light, schematically shown with rays 351, 352, and 353, majority of which (e.g. greater than 80-90%) is refracted and reflected by the re-directing structure 330 to be incident onto the diffusing reflectors 320 and 322. In turn, the diffusing reflectors 320 and 322 diffusively reflect the light incident on them. This is illustrated by tracing, for example, the ray 352.

The ray 352 has three segments: 352a, 352b, and 352c. The segment 352a illustrates a segment of the ray emitted by the LED die 312 before it is refracted at the boundary between the material filling the gap 335 and the re-directing structure 330. Note that, while this is not illustrated in Fig. 3B in order not to clutter the drawings, the segment 352a may also be refracted at the boundary between the dome 314 and the material filling the gap 335, depending on the refractive indices of the respective materials at the boundary. The segment 352b illustrates a segment of the ray 352 after it was refracted at the boundary between the material filling the gap 335 and the re-directing structure 330 and before it exits the re-directing structure 330. Finally, the segment 352c illustrates that the redirecting structure 330 guides the ray 352 to be incident on the diffusing reflector 322 at a point 362. As shown in Fig. 3B with arrows originating from the point 362, at the point 362 the diffusing reflector 322 diffusively reflects the ray 352 in different "vertical" directions.

While Fig. 3B illustrates rays to be guided onto the diffusing reflector 322, on the right side of the LED arrangement 300, similar illustrations and descriptions could be extended to the diffusing reflector 320, on the left side of the LED arrangement 300.

Preferably, the re-directing structure 330 re-directs light emitted by each LED in such a manner that equal portions are incident on the diffusing reflectors 320 and 322. In a lamp having several LEDs this would allow for the uniform light distribution between the LEDs.

The re-directing structure 330 may be designed to guide most of the light generated by the LED 310 to be incident on the diffusing reflectors 320 and 322. The optimal fraction depends on the acceptable compromise between luminance uniformity and efficiency, 100 % for best efficiency, and a fraction equal to the ratio of the length of the redirection structure to the LED pitch for optimal luminance uniformity (the afore mentioned spot uniformity). Optionally, at least a portion of the bottom (i.e. on the side towards the surface on which the LEDs are disposed) of the re-directing structure 330 may be made at least partially reflective in order to prevent absorption of light which would lower efficiency.

Fig. 3C illustrates the same embodiment as shown in Fig. 3B, but on a smaller scale, so it can be seen that the re-directing structure 330 guides the ray 351 to be incident on the diffusing reflector 322 at a point 361, where the ray 351 is diffusively reflected in different vertical directions shown with arrows originating from the point 361.

Fig. 4A illustrates a three-dimensional view of a LED arrangement 400 with upward leakage, according to one embodiment of the present invention and Fig. 4B illustrates a cross-sectional side view of the LED arrangement 400 of Fig. 4A, similar to the cross- sectional side view shown in Fig. 3B. The LED arrangement 400 may also be used as the portion 290 in the lamp 280.

As shown in Figs. 4 A and 4B, the LED arrangement 400 includes a LED 410 comprising a LED die 412 and a dome 414, diffusing reflectors 420 and 422, and a redirecting structure 430. The LED 410, the LED die 412, the dome 414, and the diffusing reflectors 420 and 422 may be analogous to the LED 310, the LED die 312, the dome 314, and the diffusing reflectors 320 and 322, respectively, described above. Therefore, all of the discussions above with respect to these elements are applicable here and, in the interest of brevity, are not repeated here.

The re-directing structure 430 is similar to the re-directing structure 330, therefore all of the discussions above with respect to the structure 330 are applicable here, but there are also some differences.

One difference is that the re-directing structure 430 includes a segment 432 from which a portion of light emitted by the LED 410 may "leak out" (i.e., escape the structure 430 without being guided to be incident on the diffusing reflectors 420 and 422), as is shown with a ray 433. The ray 433 may be incident on an optional diffusing cover 470 that could cover the re -directing structure 430 as shown in Fig. 4B. Such a diffusing cover 470 may be configured to diffusively transmit light incident thereon (similar to the diffusing cover 270, described above).

Another difference is that sides 434 and 436 of the re -directing structure 430 may be curved, as shown in Fig. 4B, as opposed to the analogous side of the re-directing structure 330 shown in Fig. 3B. In certain cases, this may improve the TIR behavior and may reduce the leaked fraction.

Fig. 5A illustrates a three-dimensional view of a LED arrangement 500 with upward leakage, according to one embodiment of the present invention and Fig. 5B illustrates a cross-sectional side view of the LED arrangement 500 of Fig. 5A, similar to the cross- sectional side view shown in Fig. 4B. The LED arrangement 500 may also be used as the portion 290 in the lamp 280.

As shown in Figs. 5A and 5B, the LED arrangement 500 includes a LED 510 comprising a LED die 512 and a dome 514, diffusing reflectors 520 and 522, and a re- directing structure 530. The LED 510, the LED die 512, the dome 514, and the diffusing reflectors 520 and 522 may be analogous to the LED 310, the LED die 312, the dome 314, and the diffusing reflectors 320 and 322, respectively, described above. Therefore, all of the discussions above with respect to these elements are applicable here and, in the interest of brevity, are not repeated here.

The re-directing structure 530 is similar to the re-directing structure 430, therefore all of the discussions above with respect to the structure 430 are applicable here, including the discussions with respect to the segment 432 and the ray 433 analogous to a segment 532 and a ray 533 illustrated in Fig. 5B, but there are also some differences.

One difference is that the re-directing structure 530 further includes segments 542 and 544 from which portions of light emitted by the LED 510 may also "leak out," as is shown for the segment 544 with a ray 545. The ray 545 may also be incident on an optional, possibly intermediate diffusing cover 570, not being the outside cover of the lamp, that could cover the re-directing structure 530 as shown in Fig. 5B. Such a diffusing cover 570 may be configured to diffusively transmit light incident thereon (similar to and possibly in addition to the diffusing covers 270 and 470, described above). If the cover 570 is implemented as an intermediate diffuser, the purpose is both to suppress the glare non-uniformity and to reduce the spot non-uniformity. Of course, an optional intermediate diffuser can also be applied in the embodiment shown in Fig. 4. The shape can deviate from that in the drawing.

The embodiments described above have all illustrated the LED including a light emitting die covered with a dome. The LED arrangements 300, 400, and 500 may also be implemented without including the domes 314, 414, and 514. Instead, the re-directing structure itself may be used to perform the functions of the dome over the light emitting die. In such embodiments, the re-directing structure may be referred to as a "primary" optical component and may be disposed either immediately over the light emitting die (i.e., be in contact with the die, no gap between the LED and the re-directing structure, such as e.g. the gap 335 shown in Fig. 3B) or may encompass the die with a gap (similar to e.g. the gap 335).

Further, LED arrangements described above could also be made rotationally symmetric with respect to all angles. One such embodiment is shown in Figs. 6A and 6B. Fig. 6A illustrates a three-dimensional view of a rotationally symmetric LED arrangement 600, according to one embodiment of the present invention and Fig. 6B illustrates a cross- sectional side view of the LED arrangement 600 of Fig. 6A.

As shown in Figs. 6A and 6B, the LED arrangement 600 includes a LED 610 comprising a LED die 612 and a dome 614, diffusing reflectors 620 and 622, and a re- directing structure 630. The LED 610, the LED die 612, the dome 614, and the diffusing reflectors 620 and 622 may be analogous to the LED 310, the LED die 312, the dome 314, and the diffusing reflectors 320 and 322, respectively, described above. Therefore, all of the discussions above with respect to these elements are applicable here and, in the interest of brevity, are not repeated here.

The re-directing structure 630 is similar to the re-directing structure 330, therefore all of the discussions above with respect to the structure 330 are applicable here. However, the re -directing structure 630 is rotationally symmetric with respect to rotations of all angles around an axis 655. Therefore, any cross-section of the LED arrangement 600 taken along any arbitrary plane that includes the axis 655 would look like the cross-section taken along the plane 650 shown in Fig. 6B. For each of these cross-sections, similar reasoning may be applied in analyzing how the light emitted by the LED 610 is guided in the LED arrangement 600.

Since the re-direction structure 630 may be configured to re-direct light backwards around the entire structure 630, in one embodiment, instead of the diffusing reflectors 620 and 622, a single diffusing reflector may be provided that surrounds the redirecting structure 630. In that manner, light incident on such a diffusing reflector all around the re-directing structure 630 could be diffusively reflected. Such an embodiment could be particularly beneficial for areal lamps, where e.g. four or 9 LED arrangements like the one shown in Fig. 6 could be arranged in a square grid to act together as an areal light source or e.g. three LED arrangements like the one shown in Fig. 6 could be arranged in a triangular grid to also act together as an areal light source. Persons skilled in the art will recognize that there are various ways for placing such LED arrangements.

In another embodiment the re-directing structure 630 may comprise a central cylindrical segment (not shown) for leaking out light similar to the segments 432 and 532. Moreover, such an embodiment could optionally also include a peripheral circular segment (not shown) at the rim of the re-directing structure 630 for leaking out light similar to the segments 542 and 544. In addition, an optional intermediate diffusing cover similar to cover 570 may be applied over re-directing structure 630.

TIR optics with optimized incoupling structure

The LED arrangements described above employ re-directing structures to redirect at least a part of the light beams emitted by a LED in a substantially vertical direction to propagate in a substantially horizontal downwards or horizontal direction by reflecting the light beams incident on the outer surface of the re-directing structures by TIR. As used herein, the term "inner surface" of a re-directing structure refers to surfaces 391, 491, 591, and 691 illustrated in Figs. 3B, 4B, 5B, and 6B, respectively, while the term "outer surface" of a re -directing structure refers to surfaces 392, 492, 592, and 692 illustrated in Figs. 3B, 4B, 5B, and 6B, respectively.

EP 0 945 673 Al discloses a TIR-based light guide, illustrated in Fig. 7, for guiding the light beams emitted by a top-emitting LED in a substantially vertical direction to propagate in a horizontal and/or horizontal downwards direction. As shown in Fig. 7, a light guide 720 having a through hole 750 of an inverted triangular shape above a top-emitting LED 730 is disposed on a substrate 740. As shown in Fig. 7, the light guide 720 has a dome- shaped inner surface 770 surrounding the LED 730, a top surface 710, and a pair of opposite reflecting surfaces 780 radially extending from the inner surface 770 to form a radial reflection surface, where sides 750A of the through hole 750 are used to re-direct, by TIR, the light emitted by the LED in a longitudinal direction of the light guide.

One problem with the light guide illustrated in Fig. 7 is that the resulting structure is relatively thick, which is undesirable for applications requiring thin building height or applications where the incoupling structure is part of the light guide and where, therefore, the thickness should be limited for manufacturability reasons. In addition, no attention seems to be given to the extended size of LED's emitting surface, which, as explained below, may lead to uncontrolled light leakage from the light guide. Yet another problem is that complexity is added by the shown symmetry where additional side mirrors are required to couple light into the light guide.

Described below is an approach that helps improving on at least some of these problems by modifying the shape of an inner surface of a re-directing structure encompassing a LED. Embodiments described above are particularly advantageous for top-emitting LEDs. Fig. 8A illustrates a three-dimensional view of a LED arrangement 800 with a modified inner surface of a re -directing structure 830, according to an embodiment of the present invention. As shown in Fig. 8A, a plane 850 is a plane of symmetry for the LED arrangement 800 and Fig. 8B illustrates a cross-sectional side view in the plane 850 of the LED arrangement 800 shown in Fig. 8A, similar to the cross-sectional side view shown in Fig. 3B.

In one embodiment, similar to the LED arrangement 300, the LED arrangement 800 may be used as the portion 290 in the lamp 280. In other embodiments, the re-directing structure 830 can be part of a light guide, where the re-directing structure would serves to couple all of the light emitted by the LED into a longer piece of transparent material guiding the light further away from the LED position, as schematically shown on Fig. 8C.

As shown in Figs. 8 A and 8B, the LED arrangement 800 includes a LED 810 comprising a LED die 812 and a dome 814, and a re-directing structure 830. The LED 810, the LED die 812, and the dome 814 may be analogous to the LED 310, the LED die 312, and the dome 314, respectively, described above. Therefore, all of the discussions above with respect to these elements are applicable here and, in the interest of brevity, are not repeated here. The LED arrangement 800 could also include diffusing reflectors (not shown in Figs. 8A and 8B) similar to the diffusing reflectors 320 and 322 illustrated and described in Fig. 3B, and therefore, all of the discussions above with respect to the diffusing reflectors are applicable here and will not be repeated.

The re-directing structure 830 comprising a body having an inner surface 891 and an outer surface 892, the inner surface 891 forming a chamber around the LED 810 is similar to the re-directing structure 330, therefore all of the discussions above with respect to the structure 330 are applicable here, but there are also some differences.

One difference is that, the inner surface 891 has a sharp peak 838 above the

LED 810. Angle 839 illustrates an opening angle of the peak 838, described in greater detail below.

As shown in Fig. 8B with a chamber 835, in the illustrated embodiment, the inner surface 891 of the re-directing structure 830 encompasses the LED 810 without being in physical contact with the LED 810. Thus, the chamber 835 is the space enclosed between the dome 814 (or the die 812, if the dome 814 is absent and the re-directing structure 830 acts as "primary optics" being a part of the LED package) of the LED 810 and the re-directing structure 830. Similar to the gap 335 described above, in various embodiments, the chamber 835 may be filled with air or with a material having suitable optical properties. In the latter case, this may require a different shape of the redirecting structure 830.

In operation, the LED die 812 emits light in a substantially vertical direction (i.e., upwards) which is intended to be re-directed by the re-directing structure 830 in a substantially horizontal and/or horizontal downwards (or backwards) direction. As used herein, the term "horizontal downwards" is used to describe the direction towards the place on which the LED die is disposed. The re -direction may be illustrated by tracing one of the light beams emitted by the LED die 812, a ray 851 , shown in Fig. 8B.

As shown, the ray 851 includes three segments: 851a, 851b, and 851c. The segment 851a illustrates a segment of the ray 851 emitted by the LED die 812 before it is refracted at the boundary between the material filling the chamber 835 and the inner surface 891. Note that, while this is not illustrated in Fig. 8B in order not to clutter the drawing, the segment 851a may also be refracted at the boundary between the dome 814 and the material filling the chamber 835, depending on the refractive indices of the respective materials at the boundary. The segment 851b illustrates a segment of the ray 851 refracted at the boundary between the material filling the chamber 835 and the inner surface 891 and being incident on the outer surface 892. Finally, the segment 851c illustrates that the ray 851 is being reflected at the outer surface 892 by TIR, thus re-directing the ray 851 from propagating in a substantially vertical direction to propagate in a substantially horizontal or backward direction.

Shaping the inner surface 891 to include the peak 838 allows operation of the LED arrangement 800 where all of the light beams emitted by the LED die 812 that are incident on the outer surface 892 after having been refracted at the inner surface 891 may be reflected at the outer surface 892 by TIR. The resulting structure is advantageous in comparison with the structure illustrated in Fig. 7 because uncontrollable light leakage from the re-directing structure 830 is significantly reduced while the overall thickness of the structure is minimized since there is no need to include holes in the re-directing structure that re-direct the light, as was done in the structure of Fig. 7 and since there is no need to increase the thickness of the re -directing structure to the point that the LED can be considered to be a point source emitter.

The advantages of having an inner surface of a re-directing structure including a sharp peak above a LED and how such a shape of the inner surface may be arrived at will now be explained with reference to Figs. 9-14. Fig. 9 provides a schematic illustration of a LED arrangement 900 used in the description of Figs. 10-14. As shown, the LED arrangement includes a LED 910 and a redirecting structure 930 having an inner surface 991 and an outer surface 992. In an embodiment, the LED 910 and the re -directing structure 930 could be analogous to the LED 810 and the re-directing structure 830 described above and, therefore, their detailed descriptions are not repeated here.

While the inner surface 991 is shown in Fig. 9 as a dome, this is not relevant for the purpose of explaining the results shown in Figs. 10-14 and, in fact, as explained below the shape of the inner surface 991 may be different. Similarly, while the outer surface 992 is shown to have a sandglass shape, this shape may also be different, depending on e.g. the desired radiation pattern. The inner surface 991 is merely shown to illustrate that "inner surface" is the surface of the re-directing structure 930 that partially encompasses the LED 910, while the outer surface 992 is shown to illustrate that "outer surface" is the TIR surface adapted to reflect light beams incident thereon by TIR. An angle between dashed lines 932 and 933 is referred to herein as an "embossing angle" of the re -directing structure 930.

In the discussions of Figs. 10-14, the LED 910 is either considered to be a "point source" emitter (i.e. all of the light beams emitted by the LED's die are considered to originate from a single point), which is illustrated in Fig. 9 with the LED 910 being a circle, or an "extended source" emitter (i.e., the light beams emitted by the LED's die are considered to originate not from a single point, but from different points of the emitting surface of the die), which is illustrated in Fig. 9 with the LED 910 being a dashed rectangle.

Coordinate system used in the explanations of Fig. 10, 11 , 13 and 14 is shown with the x-axis and the y-axis, where the point (0,0) of the coordinate system is considered to be at the center of the emitting surface of the LED 910 (be it a point source or an extended source emitter), the x-axis is used to indicate the position, in arbitrary units of length, and the y-axis is used to indicate thickness "t" of the re -directing structure 930, also measured in arbitrary units of length. As used herein, the term "thickness" of the re-directing structure refers to the distance from the x-axis (typically from the substrate on which the LED 910 and the re-directing structure 930 are disposed) to the outer surface 992, measured in the direction of the y-axis. Thus, thickness tm a x illustrated in Fig. 9 shows the point where the thickness of the re-direction structure 930 is at its maximum (thickness = max.thickness) and thickness to illustrated in Fig. 9 shows the thickness of the re-directing structure 930 at its minimum, referred to herein as a "starting thickness" of a re-directing structure. For the sandglass- shaped re-directing structure illustrated in Fig. 9, the starting thickness happens to be measured along the axis of symmetry of the beam pattern of the LED 910 (i.e., above the center of the LED 910). The starting thickness may be given by e.g. the height of the LED chamber (i.e, the height of the dome 914 encompassing the LED die 912) and the minimum material thickness of the material of the re-directing structure 930 which has the necessary mechanical characteristics or is given by manufacturing reasons.

Note that, as used herein, the word "maximum" in the term "maximum thickness" refers to the thickness of the re-directing structure being at its maximum and that the "maximum thickness" is actually the minimum value of the thickness of the re-directing structure that would allow all light beams incident on the outer surface 992 to be reflected with TIR.

Using Snell's law and light propagation laws, a set of appropriate trigonometric equations can be established describing the ray paths of light emitted at different angles from different spots on the emitting surface of the LED travelling to the boundaries formed by the inner and outer surfaces of the re-directing structure. Including information regarding refractive indices of the materials on different sides of the boundaries formed by the inner and outer surfaces and information regarding the shape of the inner surface in a manner known in the art, a shape of the outer surface 992 may be determined that would allow all of the light beams incident on the outer surface 992 to be reflected via TIR.

In the following discussions, the re-directing structure 930 is assumed to be made of a material having a refractive index n and to be surrounded by air (i.e., surrounded by a material having a refractive index equal to 1).

To calculate the outer surface just fulfilling the TIR conditions, starting point will be above the center of the LED 910. When the refractive index of the re-directing structure 930 is equal to 1.49 (e.g. the re-directing structure 930 is made from PMMA) and the LED 910 is considered to be a point source emitter, the embossing angle of the hourglass arrangement could be calculated to be equal to 95.7 degrees. The next coordinate points (x,y) of the outer surface can be calculated from

r '' :

J 0 J I" * · ' " " (1) In equation (1), t 0 represents the starting thickness of the re -directing structure 930, ' TIR IS the minimum incident angle to fulfill TIR condition and » R a y is the emission angle from the LED 910. For a point source located at (0,0), · R AY is directly linked to the coordinates of the outer surface and the equation of the outer surface becomes:

Fig. 10 provides a computation result of the cross-section (x, y(x)) of such a shape of the outer surface 992 satisfying the TIR condition when the LED 910 is considered to be a point source emitter. In the simulation of Fig. 10, the re-directing structure 930 is such that the inner surface 991 forms a dome chamber encompassing the LED 910 or such that the LED 910 is immersed within the re-directing structure 930. As used herein, the term

"immersed" is used to describe an embodiment where the inner surface 991 is in direct contact with the LED 910. As becomes clear from the inspection of the simulation result of Fig. 10, in this case, the outer surface 992 could as well be chosen to be essentially a parabola (with a minimum height to satisfy TIR condition) if the resulting light beam pattern after redirection is meant to be essentially collimated .

The thinnest re -directing structure 930 above back plane based on the TIR condition (see equation (2) above), with starting thickness t 0 above the center of the LED 910, will have as maximum thickness of the re-directing structure 930:

where k = : l/(:¾ 2 — 1}

However, the LED 910 cannot always be considered to be a point source emitter. This consideration becomes especially important when the size of the emitting surface of the LED 910 is comparable with the starting thickness of the re-directing structure 930. For a LED 910 with a given size of the emitting surface (source_size), at a height h above the center of the LED 910 the incident angles (on the outer surface 992) from source _ size

the emitting surface will be distributed between - arctan 2^ , which, at a height equal to the size of the emitting surface, will lead to emitting angles being distributed from - 26 degrees to + 26 degrees above the center of the LED 910. This means that the embossing angle of the re-directing structure 930 would decrease to 55 degrees (for the re-directing structure 930 made from PMMA) to satisfy the TIR condition. As can already be made clear from a simple geometrical inspection of the relationship between the embossing angle and the maximum thickness of the re-directing structure 930 illustrated in Fig. 9, the smaller the embossing angle, the greater the maximum thickness of the re-directing structure 930. Thus, a decreased embossing angle leads to a significantly increased thickness of the re -directing structure 930 for the TIR condition to still be satisfied. Equation (2) would be changed here to include the extended source emission position to

. . f* fx— source size/2 Y\

y{xj = t■÷- I tan f & TlR — arctan | j | dx

(4)

This case is illustrated in Fig. 11 , providing a computation result for a cross- sectional shape of the outer surface 992 satisfying the TIR condition when the LED 910 is considered to be an immersed extended source emitter (the dashed line in Fig. 11). For comparison, the simulation result of Fig. 10 (i.e., the LED 910 is considered to be a point source emitter) is also included in Fig. 11 (the solid line in Fig. 11).

When the LED 910 is considered to be immersed within the re-directing structure 930, the solution for the maximum thickness of the re-directing structure 930 can still be written analytically, showing the dependence on source size and optics' size:

max, thickness

Fig. 11 illustrates that when only the outer surface 992 of the re-directing structure 930 is optimized to make sure that all light beams incident on the outer surface 992 are reflected by TIR, thickness of the re-directing structure 930 has to increase when the size of the emitting surface of the LED 910 is such that the LED 910 may no longer be considered to be a point source emitter. Just how big should the size of the emitting surface of the LED 910 be when it may no longer be considered to be a point source emitter is illustrated in Fig. 12.

Fig. 12 illustrates dependence of the optics size on the size of the emitting surface of the LED 910, where the term "optics' thickness" refers to the maximum thickness of the re-directing structure 930. The x-axis in Fig. 12 is used to indicate the ratio between the starting thickness of the re-directing structure 930 (i.e., to) and the size of the emitting surface of the LED 910, while the y-axis is used to indicate the ratio between the maximum thickness of the re-directing structure 930 when the LED 910 is considered to be an extended source emitter and the maximum thickness of the re-directing structure 930 when the LED 910 is considered to be a point source emitter (i.e., the ratio between values calculated according to equation (5) and equation (3) provided above).

Point A in Fig. 12 illustrates that when the size of the emitting surface is approximately twice as large as the starting thickness of the re-directing structure 930 (i.e., the ratio depicted along the x-axis of Fig. 12 is equal to 0,5), the maximum thickness of the re-directing structure increases approximately 3 times compared with the maximum thickness necessary to satisfy TIR condition when the LED 910 can be considered to be a point source emitter. This means that when the ratio to/source_size is equal to 0,5, the re-directing structure 930 having a maximum thickness less than the value calculated according to equation (5), provided above, will not be able to satisfy TIR condition for all of the incident angles and some of the light will be leaked out.

Fig. 12 further illustrates that when the starting thickness of the re-directing structure 930 is increased with respect to the size of the emitting surface of the LED 910, the ratio between the optics size for the extended source and a point source emitter decreases. Thus, as shown in Fig. 12 with a point B, when the starting thickness of the re-directing structure 930 is 2,5 times bigger than the size of the emitting surface of the LED 910, the maximum thickness of the re-directing structure only needs to be increased approximately 1.25 times to satisfy the TIR condition in comparison with maximum thickness when the LED 910 could be considered a point source.

Point C in Fig. 12 corresponds to the scenarios depicted in Fig. 11 where the ratio between the starting optics' thickness and the source size is equal to 1,5 because in Fig. 11, t 0 is shown to be equal to 1,5 units of length while the half of the extended source is shown to be equal to 0,5 units of length. Fig. 11 illustrates only a half of the extended source since, as described above, point (0,0) coincides with the center of an LED. As illustrated in Fig. 12 with point C, for such a ratio between the starting optics' thickness and the source size, the ratio between optics' thickness calculated for the extended source and for the point source is a little bit less than 1,5. This is also clear from comparing, in Fig. 11, the maximum thickness of the dashed line and the maximum thickness of the solid line.

Based on Fig. 12, it can be concluded that when the re-directing structure 930 is made thick enough, any LED 910 may be considered to be a point source and shape of the outer surface 992 may be determined so that TIR condition would be satisfied for all light beams incident thereon. However, as described in the background section, it may be desirable to make the re-directing structure 930 as thin as possible. To that end, employing a dome- shaped inner surface 991 (i.e., the inner surface 991 shaped so as to form a dome around the LED 910) allows decreasing the overall thickness of the re -directing structure 930, in comparison with the immersed LED described in Fig. 11, while still satisfying the TIR condition. This is illustrated in Fig. 13, providing a simulation result for a cross-sectional shape of the outer surface 992 satisfying the TIR condition when the LED 910 is considered to be an extended source emitter with the inner surface 991 forming a dome chamber encompassing the LED 910 (the dotted-dashed line in Fig. 13). For comparison, the simulation results of Fig. 10 (i.e., the LED 910 is considered to be a point source emitter) and

Fig. 11 (i.e., the LED 910 is considered to be an extended source emitter) are also included in

Fig. 13 (the solid line and the dashed line, respectively, in Fig. 13).

When the LED 910 is considered to be encompassed by a dome-shaped inner surface 991, the solution for the maximum thickness of the re-directing structure 930 can no longer be written analytically. Instead, the equation for the outer surface 992 that would satisfy TIR condition for all incident beams, given the dome shape of the inner surface 991 needs to be solved numerically, which would read:

f A f — 3- .,Y\

yi x ) = f.-. ÷ J tsn I # iS — arcr_m f { ) x

J r V * \v— ¥.,··' i

" (6)

In equation (6), (¾, y c ) are the coordinates of the ray's intersection with the dome interface before being incident on the outer surface in (x, y).

As is clear from Fig. 13, employing a dome-shaped inner surface 991 allows decreasing the overall thickness of the re-directing structure 930 compared to the necessary minimum thickness for the immersed extended source scenario (dashed line in Fig. 13) but the overall thickness is still significantly greater than that for the point sources scenario (solid line in Fig. 13). Only by shaping the inner surface 991 beyond a dome shape, that is, by creating a peak above the LED 910, can the light beams be sufficiently refracted at the inner surface boundary to be reflected by TIR at the outer surface 992, without uncontrolled leakage and with minimum increase in the thickness of the re-directing structure 930. When the inner surface 991 is shaped as shown in Fig. 8B (such a surface may be referred to as 'peak-shaped' surface), then the numerical simulation similar to those shown in Fig. 13 would yield a shape of the outer surface 992 closest to the shape of the outer surface 992 for the point source scenario, i.e., with the minimum overall thickness of the re-directing structure 930.

Similar to the dome-shaped inner surface, the solution for the maximum thickness of the re-directing structure 930 for the peak-shaped inner surface 991 cannot be written analytically, but may be obtained as a numerical solution.

To calculate the shape of the inner chamber, the inner surface's slope should be oriented so as to "rotate" the rays emitted from the edge of the source's surface into the direction of rays coming from the center (as the outer TIR surface was originally designed on that point). In other words, the inner surface slope should be oriented so that the rays emitted from the edge of the source's emitting surface would be refracted by the inner surface at such an angle that it would appear as if they were emitted from the center of the source's emitting surface. As used herein, the term "rotation" in the context of "rotation" of the rays emitted from the edge of the emitting surface is used to describe the change in the direction of such rays after they are refracted at the boundary with the inner surface due to the change in the shape of the inner surface.

The corresponding equation then becomes

In equation (7), · ι ηηεΓ is the angle that the slope of the inner interface at coordinates (Xi nn er,yinner) forms with the x-axis, · targe t is the target angle (i.e., angle as defined by rays emitted from the center position of the source) of the source's edge ray in the medium of refractive index n. The shape of the inner surface can then be integrated as

In equation (8), yo is the starting height of the inner chamber above the center of the LED for the two-sided type redirecting structures as described here (i.e., the distance, measured in the direction of the y-axis, from the x axis to the peak of the inner chamber, such as the peak 838). Note that, depending on the total source size/ optics thickness ratio, when approaching the edge of the source, the slope increases such that the chamber will be reduced to zero thickness. To avoid this, the slope could be chosen smaller than necessary and the outer surface would need to be modified, leading to a slightly thicker solution of the optics.

The thickness increase is, however, much less than with a dome-shaped inner surface, as the starting slope of the outer surface, above the center of the source, has been reduced significantly.

This is illustrated in Fig. 14, providing simulation result of the cross-sectional shape of the outer surface 992 satisfying the TIR condition when the LED 910 is considered to be an extended source emitter with the inner surface 991 forming a peak shaped chamber encompassing the LED 910 (the dotted-dashed line in Fig. 14, solution to the equations (7) and (8)). For comparison, the simulation results of Fig. 10 (i.e., the LED 910 is considered to be a point source emitter) and Fig. 11 (i.e., the LED 910 is considered to be an extended source emitter) are also included in Fig. 14 (the solid line and the dashed line, respectively, in Fig. 14). This numerical simulation yields thus a shape of the outer surface 992 closest to the shape of the outer surface 992 for the point source scenario, i.e., with the minimum overall thickness of the re-directing structure 930. Persons skilled in the art will recognize that, depending on e.g. the final radiation pattern and mechanical constraints, the re-directing structure can be described by shapes different than the shapes illustrated in the exemplary embodiments herein. However, irrespective of the particular shape of the re -directing structure, reducing the otherwise steep embossing angle in the center above the LED is the most important consideration for the final thickness of the re-directing structure, when the LED is considered to be an extended source. The peak-shaped inner surface contributes efficiently to this reduction by "rotating" the incoming rays from the edge of the source into a direction that more easily can fulfill the TIR condition at the outer surface of the re-directing structure. The peak-shaped inner surface should have an average opening angle (such as e.g. the opening angle 839 illustrated in Fig. 8B) so that, in a cross- sectional view like the one shown in Fig. 8B, a straight line drawn between the peak 838 and the edge of the LED die 812 would not cross the inner surface 891. For a starting height y 0 of the inner surface this condition reads:

opening angle = 2 · inner (0, yo ) = 2 atan(source size/2/yo)

Further, to allow the "rotation" of the beam emitting from the edge of the source, the angle of the inner surface will be in the center for an inner surface starting height equal to the source size and for refractive index of n=l .49:

2 · inner (0, source size) = 74 degrees (instead of 180 degrees as given for a dome shaped solution).

In practice, when a re-directing structure is manufactured by e.g. injection moulding, it could happen that the peak in the inner surface instead of being a sharp peak with an opening angle designed as described above is actually rounded on the very top (as shown in some exemplary structures illustrated in Fig. 18). In such a case the opening angle could be, in reality, equal to 180 degrees (because the peak itself forms a dome at the center of the inner surface of the re-directing structure). However, persons skilled in the art would still recognize that how to apply the teachings disclosed in the present invention regarding introducing an appropriate peak to the inner surface of a re -directing structure even when the peak is, in practice, rounded.

A second part of the inner surface can rather be given by mechanical constraint and minimum Fresnel reflection for rays already emitted from the LEDs in the final target direction. With these starting points in mind, optical raytracing software may be employed to find the overall compromise.

Figs. 15A-15D illustrate how, given the same maximum thickness and the same starting thickness of the re-directing structure 930 and the same shape of the outer surface 992, light beams emitted from near the edge of the emitting surface of the LED 910 could be leaked out when a dome-shaped inner surface 991 is employed (see Figs 15B and 15D). In contrast, when a peak-shaped inner surface 991 is employed, the same light beams would be reflected at the outer surface 992 by TIR (see Figs. 15A and 15C). Thus, shaping the inner surface 991 with respect to the outer surface 992 allows achieving that all of the light beams refracted at the inner surface 991 and incident on the outer surface 992 are reflected at the outer surface 992 by TIR.

Returning back to the LED arrangement illustrated in Figs. 8 A and 8B, for applications that require that some of the light is leaked out of the LED arrangement 800, additional structures may be introduced to the re-directing structure 830 that allow controlled light leakage in pre-determined locations with respect to the LED 810, according to one embodiment of the present invention. To that end, Fig. 16 illustrates a cross-sectional side view in the plane 850 of an LED arrangement 1600, which is similar to the LED

arrangement 800. The LED arrangement 1600 includes a LED 1610 and a re-directing structure 1630, similar to the LED 810 and the re-directing structure 830, respectively, described above. Therefore, in the interests of brevity, a description of the LED 1610 and the re-directing structure 1630 is not repeated here. The main difference between the LED arrangement 800 depicted in Figs. 8A-8B and the LED arrangement 1600 is that the latter also includes rings 1603 on an outer surface 1692 of the re-directing structure 1630. The rings 1603 are adapted to provide controlled leakage of a portion of light beams emitted by the LED 1610. Alternatively or additionally, controlled leakage of light from the re-directing structure may also be achieved by introducing different corrugations in the outer surface of the re-directing structure, as is schematically shown in Fig. 17.

The embodiments described above have all illustrated the LED including a light emitting die covered with a dome. The LED arrangements 800 and 1600 may also be implemented without including the domes 814 and 1614. Instead, the re-directing structure itself may be used to perform the functions of the dome over the light emitting die. In such embodiments, the re-directing structure may be referred to as a "primary" optical component.

Further, LED arrangements described above could also be made rotationally symmetric with respect to all angles and/or, while the illustrated embodiments are particularly advantageous for use with the top-emitting LEDs, the teachings of the present invention could also be applied for use with side-emitting LEDs.

In addition, while the embodiments described herein all include a sharp peak in the inner surface of the re-directing structure, embodiments with the inner surface comprising a peak of a different shape are also within the scope of the present invention. Fig. 18 illustrates portions of re -directing structures with inner surfaces comprising peaks of different shapes, according to various embodiments of the present invention.

While the description of the modified inner surface of a re-directing structure was provided above with reference to the LED arrangement 300, considerations similar to those provided with respect to Figs. 8 A- 18 could be applied to modify the LED arrangements 400, 500, and 600 so that the inner surfaces 491, 591, and 691, respectively, would also include a peak. Since a person skilled in the art would easily recognize how to adapt the considerations provided with respect to Figs. 8A-18 to other shapes of the re-directing structure, detailed discussion of such adaptations is not necessary here.

While the forgoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. Therefore, the scope of the present invention is determined by the claims that follow.