Field of the disclosure

The disclosure relates generally to illuminating engineering. More particularly, the disclosure relates to an optical device for modifying a light distribution pattern of a light source that can be, for example but not necessarily, a light emitting diode “LED”.

Background

Distribution of light produced by a light source can be important or even critical in some applications. The light source can be, for example but not necessarily, a light emitting diode“LED”, a filament lamp, or a gas-discharge lamp. Figure 1 a shows a schematic illustration of a street lighting application where streetlamps 122 and 123 are arranged to illuminate a road 120. Figure 1 b shows a view of a section taken along the line A1 - A1 shown in figure 1 a, and figure 1 c shows a view of a section taken along the line A2 - A2 shown in figure 1 a. Each of the streetlamps 122 and 123 may comprise, for example, a lighting fixture that comprises a plurality of light sources, e.g. light emitting diodes“LED”, and optical devices each of which being arranged to modify the light distribution pattern of one or more of the light sources. An exemplifying optical device 101 according to the prior art is illustrated in figures 1 e and 1f where figure 1f shows a view of a section taken along the line A - A shown in figure 1 e. A light source 102 is arranged to radiate first light beams to a first geometric quarter-space 103 and second light beams to a second geometric quarter-space 104, where the first and second geometric quarter-spaces are defined by mutually perpendicular geometric planes 105 and 106 so that the geometric plane 105 constitutes a boundary between the first and second geometric quarter- spaces 103 and 104. In figures 1 e and 1f, some of the first light beams are depicted with dot-and-dash line arrows and some of the second light beams are depicted with dashed line arrows. It is to be noted that the above-mentioned geometric planes 105 and 106 are mere geometric concepts for illustrative purposes only but not physical elements of the optical device 101 or of the light source 102. The geometric plane 105 is parallel with the yz-plane of a coordinate system 199 and the geometric plane

106 is parallel with the xy-plane of the coordinate system 199. The optical device 101 comprises a lens-section 107 for modifying a light distribution pattern of the first light beams. The optical device 101 comprises a reflector surface 108 for reflecting at least a part of the second light beams to the first quarter-space 103 as illustrated in figures 1 e and 1f. The reflector surface 108 is a surface of a cavity 109. The geometric forms of the cavity 109 and the refractive index of the transparent material of the optical device 101 are selected so that the total internal reflection“TIR” takes place on the reflector surface 108.

Figure 1d shows polar plots illustrating simulated luminance distributions on the surface of the road 120 when optical devices of the kind described above are being used in an exemplifying situation where the distance D between the adjacent streetlamps is about 4.5 times the height H of streetlamp poles and the width W of a lane 121 is about a half of the height H of the streetlamp poles. The solid line polar plot shows the luminance distribution on the line A1 - A1 shown in figure 1 a and the dashed line polar plot shows the luminance distribution on the line A2-A2 that is on the middle of the lane 121 . Angles cpi and y2 are defined in figure 1 c and angles f3 and f ₄ are defined in figure 1 b. An ideal situation would be such that the luminance is at a suitable level and uniform on the surface of the road. In figure 1 d, a circle arc 124 illustrates a situation where the luminance is uniformly distributed.

As shown by the solid line polar plot in figure 1 d, a part of the light is not directed to the road 120 but backwards from the streetlamps. As illustrated in figure 1 f, the backwards directed light is at least partly caused by undesired reflections on a surface 1 10 that is near vertical. The near-vertical surface 1 10 is needed for enabling the reflector surface 108 to be so high in the z-direction of the coordinate system 199 that substantially all light radiated to the second geometric quarter- space 104 falls on the reflector surface 108. In principle, the lens-section 107 could be thicker in the z-direction of the coordinate system 199 so as to avoid the near- vertical surface 1 10 but a thicker lens-section would increase the attenuation caused by the optical device. Thus, a geometry which provides a reflector surface that is high enough is not free from challenges. Summary

The following presents a simplified summary in order to provide a basic understanding of some aspects of various invention embodiments. The summary is not an extensive overview of the invention. It is neither intended to identify key or critical elements of the invention nor to delineate the scope of the invention. The following summary merely presents some concepts of the invention in a simplified form as a prelude to a more detailed description of exemplifying embodiments of the invention.

In this document, the word“geometric” when used as a prefix means a geometric concept that is not necessarily a part of any physical object. The geometric concept can be for example a geometric point, a straight or curved geometric line, a geometric plane, a non-planar geometric surface, a geometric space, or any other geometric entity that is zero, one, two, or three dimensional.

In accordance with the invention, there is provided a new optical device for modifying a light distribution pattern of a light source radiating first light beams to a first geometric quarter-space and second light beams to a second geometric quarter-space, the first and second geometric quarter-spaces being defined by mutually perpendicular first and second geometric planes so that the first geometric plane constitutes a boundary between the first and second geometric quarter- spaces. An optical device according to the invention comprises:

- a lens-section for acting as a lens for modifying a light distribution pattern of the first light beams,

- a first reflector surface for reflecting a first part of the second light beams from the second geometric quarter-space to the first geometric quarter-space, and - a second reflector surface for reflecting a second part of the second light beams from the second geometric quarter-space to the first geometric quarter-space.

The above-mentioned first and second reflector surfaces are successively in a direction perpendicular to the first geometric plane so that the first reflector surface is between the first geometric plane and the second reflector surface. The first reflector surface is farther from the second geometric plane than is the second reflector surface so that an area between the first reflector surface and the second geometric plane constitutes a propagation passage for the second part of the second light beams on a route to the second reflector surface.

The above-mentioned optical device is a transparent piece that comprises:

- a first cavity for the light source,

- a second cavity whose surface constitutes the first reflector surface so that total internal reflection takes place when the first part of the second light beams arrive, from inside the transparent piece, at the surface of the second cavity, and

- a third cavity whose surface constitutes the second reflector surface so that total internal reflection takes place when the second part of the second light beams arrive, from inside the transparent piece, at the surface of the third cavity, a wall between the first and second cavities being farther from the second geometric plane than is a wall between the second and third cavities, and a part of the wall between the second and third cavities constitutes a part of the route of the second part of the second light beams to the second reflector surface. The above-described optical device that comprises the above-mentioned first and second reflector surfaces does not need to be as high as a corresponding optical device that comprises only one reflector surface because the first reflector surface, which is nearer to the light source, reflects light for which the second reflector surface would be too low. In accordance with the invention, there is provided also a new lighting fixture comprising at least one light source and at least one optical device according to the invention. The at least one light source may comprise, for example, one or more light emitting diodes“LED”. In accordance with the invention, there is provided also a new system comprising a road and at least one streetlamp comprising at least one lighting fixture according to the invention, wherein each optical device of the least one lighting fixture is positioned with respect to the road so that a geometric section line between the above-mentioned first and second geometric planes related to the optical device under consideration is substantially parallel with the longitudinal direction of the road.

A transparent piece constituting an optical device according to the invention can be manufactured for example by mold casting. In accordance with the invention, there is provided also a new mold having a form suitable for manufacturing, by mold casting, the above-mentioned single piece of transparent material.

Various exemplifying and non-limiting embodiments of the invention are described in accompanied dependent claims. Various exemplifying and non-limiting embodiments of the invention both as to constructions and to methods of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific exemplifying embodiments when read in conjunction with the accompanying drawings. The verbs“to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in dependent claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of“a” or “an”, i.e. a singular form, throughout this document does not exclude a plurality. Brief description of the figures

The exemplifying and non-limiting embodiments of the invention and their advantages are explained in greater detail below with reference to the accompanying drawings, in which: figures 1 a-1 c show a schematic illustration of a street lighting application according to the prior art, figure 1d shows polar plots illustrating simulated luminance distributions on the surface of a road shown in figures 1 a-1 c when optical devices according to the prior art are being used, figures 1 e and 1 f illustrate an optical device according to the prior art, figures 2a and 2b illustrate an optical device according to an exemplifying and non- limiting embodiment of the invention, figure 3 illustrates an optical device having an alternative mechanical structure and operating in a same way as an optical device according to an exemplifying and non- limiting embodiment of the invention, figures 4a and 4b illustrate a lighting fixture according to an exemplifying and non- limiting embodiment of the invention, figures 5a-5c illustrate a street lighting application according to an exemplifying and non-limiting embodiment of the invention, and figure 6a describes the operation of an optical device according to an exemplifying and non-limiting embodiment of the invention, and figure 6b describes the operation of an optical device according to the prior art such as shown in figures 1 e and 1f.

Figures 1 a-1 f have already been explained in the Background-section of this document.

Description of exemplifying embodiments

The specific examples provided in the description given below should not be construed as limiting the scope and/or the applicability of the appended claims. Lists and groups of examples provided in the description given below are not exhaustive unless otherwise explicitly stated.

Figures 2a and 2b illustrate an optical device 201 according to an exemplifying and non-limiting embodiment of the invention for modifying a light distribution pattern of a light source 202 that can be, for example but not necessarily, a light emitting diode “LED”, a filament lamp, or a gas-discharge lamp. Figure 2b shows a view of a section taken along the line A - A shown in figure 2a. The section plane is parallel with the xz-plane of a coordinate system 299. As illustrated in figures 2a and 2b, the light source 202 is arranged to radiate first light beams to a first geometric quarter-space 203 and second light beams to a second geometric quarter-space 204, where the first and second geometric quarter-spaces are defined by mutually perpendicular first and second geometric planes 205 and 206 so that the first geometric plane 205 constitutes a boundary between the first and second geometric quarter-spaces 203 and 204. In figures 2a and 2b, some of the above-mentioned first light beams are depicted with dot-and-dash line arrows and some of the above-mentioned second light beams are depicted with dashed line arrows. It is to be noted that the above- mentioned first and second geometric planes 205 and 206 are mere geometrical concepts for illustrative purposes only but not physical elements of the optical device 201 or of the light source 202. The first geometric plane 205 is parallel with the yz- plane of a coordinate system 299 and the second geometric plane 206 is parallel with the xy-plane of the coordinate system 299.

The optical device 201 comprises a lens-section 207 for modifying the light distribution pattern of the above-mentioned first light beams. The optical device 201 comprises a first reflector surface 208 for reflecting a first part of the above- mentioned second light beams from the second geometric quarter-space 204 to the first geometric quarter-space 203 so that total internal reflection“TIR” takes place when the first part of the second light beams arrive, from inside transparent material, at the first reflector surface 208. The optical device 201 comprises a second reflector surface 21 1 for reflecting a second part of the second light beams from the second geometric quarter-space 204 to the first geometric quarter-space 203 so that total internal reflection takes place when the second part of the second light beams arrive, from inside the transparent material, at the second reflector surface 21 1 . In addition to the light which is reflected by the reflector surface 208 or 21 1 , the light source 202 may radiate, to the second geometric quarter-space 204, light that does not fall on either one of the reflector surfaces 208 and 21 1 . The aim is, however, to minimize the amount of light which is radiated to the second geometric quarter- space 204 but which is not reflected.

As illustrated in figures 2a and 2b, the first and second reflector surfaces 208 and 21 1 are successively in a direction perpendicular to the first geometric plane 205 so that the first reflector surface 208 is between the first geometric plane 205 and the second reflector surface 21 1 . As illustrated in figure 2b, the first reflector surface 208 is farther from the second geometric plane 206 than is the second reflector surface 21 1 so that an area 219 between the first reflector surface 208 and the second geometric plane 206 constitutes a propagation passage for the second part of the second light beams on a route to the second reflector surface 21 1 . As can be understood with the aid of figure 2b, the first reflector surface 208, which is nearer to the light source 202, reflects light for which the second reflector surface 21 1 would be too low in the negative z-direction of the coordinate system 299. Therefore, the optical device 201 does not need to be as high in the z-direction of the coordinate system 299 as a corresponding optical device that comprises only one reflector surface such as e.g. the optical device 101 illustrated in figures 1 e and 1f.

As illustrated in figure 2a, the first reflector surface 208 is convex towards the first geometric quarter-space 203 so as to spread the reflected first part of second light beams to sideward directions, and the second reflector surface 21 1 is wedge- shaped and pointing towards the first geometric quarter-space 203 so as to spread the reflected second part of second light beams to the sideward directions. It is also possible to provide the first reflector surface 208 and/or the second reflector surface

21 1 with grooves and/or other undulations so as to spread the reflected light in a desired way.

The exemplifying optical device 201 illustrated in figures 2a and 2b is a single piece of transparent material. The piece of transparent material comprises a first cavity

212 for the light source 202 as illustrated in figures 2a and 2b. The piece of transparent material comprises a second cavity 209 whose surface constitutes the first reflector surface 208 so that total internal reflection “TIR” takes place, as illustrated in figure 2b, when light beams arrive at the first reflector surface 208 from inside the transparent material. The piece of transparent material comprises a third cavity 213 whose surface constitutes the second reflector surface 21 1 so that total internal reflection takes place, as illustrated in figure 2b, when light beams arrive at the second reflector surface 21 1 from inside the transparent material. As illustrated in figure 2b, a wall 214 between the first and second cavities 212 and 209 is farther from the second geometric plane 206 than is a wall 215 between the second and third cavities 209 and 213. A part of the wall 215 constitutes a part of the route of the second part of the second light beams to the second reflector surface 21 1 . A light-ingress surface of the above-mentioned part of the wall 215 can be provided with grooves and/or other undulations for spreading a light distribution pattern of the second part of the second light beams in the sideward directions. In figure 2a, one of the grooves is denoted with a reference 216. The grooves are substantially perpendicular to a geometric section line between the first and second geometric planes 205 and 206.

The above-mentioned first, second, and third cavities 212, 209, and 213 are formed so that a first surface 218 of the piece of transparent material comprises pits constituting the first, second, and third cavities 212, 209, and 213, and the first surface 218 is substantially planar on regions surrounding the pits. A second surface 230 of the piece of transparent material is shaped so that a desired light distribution is achieved. The first surface 218 can be installed for example to be against a circuit board where the light source 202 is mounted on a surface of the circuit board. In the exemplifying case illustrated in figures 2a and 2b, the piece of transparent material constituting the optical device 201 is substantially symmetric with respect to a third geometric plane which is parallel with the xz-plane of the coordinate system 299 and which coincides with the section plane related to the section view shown in figure 2b. In figure 2a, the third geometric plane is denoted with a reference 217. Asymmetric shapes are, however, also possible. The piece of transparent material can be made of for example acrylic plastic, polycarbonate, optical silicone, or glass. The method of manufacture can be for example mold casting.

Figure 3 shows a section-view of an optical device 301 for modifying the light distribution pattern of a light source 302. The section plane is parallel with the xz- plane of a coordinate system 399. The light source 302 is arranged to radiate first light beams to a first geometric quarter-space 303 and second light beams to a second geometric quarter-space 304, where the first and second quarter-spaces are defined by mutually perpendicular first and second geometric planes 305 and 306 so that the first geometric plane 305 constitutes a boundary between the first and second geometric quarter-spaces. The first geometric plane 305 is parallel with the yz-plane of a coordinate system 399 and the second geometric plane 306 is parallel with the xy-plane of the coordinate system 399. In figure 3, some of the first light beams are depicted with dot-and-dash line arrows and some of the second light beams are depicted with dashed line arrows. The optical device 301 comprises a lens-section 307 for modifying the light distribution pattern of the above-mentioned first light beams. The optical device 301 comprises a first reflector surface 308 for reflecting a first part of the above-mentioned second light beams from the second geometric quarter-space 304 to the first geometric quarter-space 303. The optical device 301 comprises a second reflector surface 31 1 for reflecting a second part of the second light beams from the second geometric quarter-space 304 to the first geometric quarter-space 303. The first and second reflector surfaces 308 and 31 1 are successively in a direction perpendicular to the first geometric plane 305 so that the first reflector surface 308 is between the first geometric plane 305 and the second reflector surface 31 1 . The first reflector surface 308 is farther from the second geometric plane 306 than is the second reflector surface 31 1 so that an area 319 between the first reflector surface 308 and the second geometric plane 306 constitutes a propagation passage for the second part of the second light beams on a route to the second reflector surface 31 1 .

In the exemplifying optical device illustrated in figure 3, the first reflector surface 308 is an outer surface of an element 331 that can be, for example, a piece of metal such as aluminum or a piece of plastics coated with a reflective layer. Correspondingly, the second reflector surface 31 1 is an outer surface of an element 332 that can be, for example, a piece of metal such as aluminum or a piece of plastics coated with a reflective layer. Therefore, the principle based on two reflector surfaces and described above with reference to figures 2a and 2b is applicable also in optical devices where reflector surfaces are implemented with non-transparent reflective material, e.g. metal. Figures 4a and 4b illustrate a lighting fixture according to an exemplifying and non- limiting embodiment of the invention. Figure 4b shows a view of a section taken along the line A - A shown in figure 4a. The section plane is parallel with the xz- plane of a coordinate system 499. The lighting fixture comprises four light sources and four optical devices 401 a, 401 b, 401 c and 401 d. Each of the optical devices is according to an exemplifying and non-limiting embodiment of the invention. In figure 4a, two of the light sources are depicted with references 402a and 402b. Each of the optical devices 401 a-401 d can be for example such as illustrated in figures 2a and 2b. Each of the light sources may comprise at least one light emitting diode “LED”. In the exemplifying case illustrated in figures 4a and 4b, the lighting fixture further comprises a circuit board 425. In this exemplifying case, the optical devices 401 a-401 d are parts of a single piece 426 of transparent material. The light sources are located on a surface of the circuit board 425 and in cavities of the optical devices 401 a-401d as illustrated in figure 4b.

Figure 5a shows a schematic illustration of a street lighting application where streetlamps 522 and 523 are arranged to illuminate a road 520. Figure 5b shows a view of a section taken along the line A1 - A1 shown in figure 5a, and figure 5c shows a view of a section taken along the line A2 - A2 shown in figure 5a. Each of the streetlamps 522 and 523 comprises one or more lighting fixtures each of which comprises one or more light sources, e.g. light emitting diodes“LED”, and one or more optical devices for modifying the light distribution pattern of the one or more light sources. Each optical device can be according to what is illustrated in figures 2a and 2b or in figure 3. Each optical device is positioned with respect to the road 520 so that a geometric section line between the first and second geometric planes related to the optical device under consideration is substantially parallel with a longitudinal direction of the road 520. The above-mentioned first and second geometric planes are defined above with reference to figure 2b and to figure 3.

Figure 6a describes the operation of an optical device illustrated in figures 2a and 2b, and figure 6b describes the operation of an optical device according to the prior art such as illustrated in figures 1 e and 1f. Figures 6a and 6b show isocandela curves on an inner surface of a sphere having an optical device and a light source substantially at its center point. On each isocandela curve, the luminous power per unit solid angle is constant. The angle f _n is defined in figure 5b, and the angle (p _h is defined in figure 5c. As can be seen in figures 6a and 6b, the optical device illustrated in figures 2a and 2b does not direct so much light backwards, i.e. to directions where the angle f _n is negative, as does the optical device illustrated in figures 1 e and 1f.

The specific examples provided in the description given above should not be construed as limiting the scope and/or the applicability of the appended claims. Lists and groups of examples provided in the description given above are not exhaustive unless otherwise explicitly stated.