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Title:
ILLUMINATION SYSTEM AND LUMINAIRE
Document Type and Number:
WIPO Patent Application WO/2011/125010
Kind Code:
A1
Abstract:
The invention relates to an illumination system (10), a luminaire and a backlighting system. The illumination system according to the invention comprises a light source (20) and a tapered reflector (30). The tapered reflector comprises an edge-wall (60) connecting the narrow end (50) and the wide end (40). The edge-wall having a light reflective surface for reflecting the light source towards the wide end. The reflective surface is made of one material and exhibits light reflective property having a non-zero diffusing component and a non-zero specular component, the specular component being at least 10% of the total reflection when the incident light is at 30° to the reflective surface. An effect of the illumination system is that a shape of a beam of light emitted by the illumination system may be adapted while maintaining a relatively low glare value.

Inventors:
TORDINI GIORGIA (FR)
Application Number:
PCT/IB2011/051402
Publication Date:
October 13, 2011
Filing Date:
April 01, 2011
Export Citation:
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Assignee:
KONINKL PHILIPS ELECTRONICS NV (NL)
TORDINI GIORGIA (FR)
International Classes:
F21K99/00; F21V7/00; F21V7/22; F21Y101/02
Domestic Patent References:
WO1999020937A11999-04-29
WO2004025172A12004-03-25
Foreign References:
US20090121238A12009-05-14
EP1936261A22008-06-25
US20080093530A12008-04-24
US6203176B12001-03-20
Other References:
None
Attorney, Agent or Firm:
BEKKERS, Joost et al. (High Tech Campus 44, AE Eindhoven, NL)
Download PDF:
Claims:
CLAIMS

1. Illumination system (10, 12, 14, 16) comprising a light source (20) and a tapered reflector (30, 32, 90), wherein

the light source (20) comprising a light-emitting surface (21) being arranged at a narrow end (50, 75) of the tapered reflector (30, 32, 90) for emitting substantially light towards a wide end (40) of the tapered reflector (30, 32, 90), and

the tapered reflector (30, 32, 90) comprising an edge-wall (60, 62, 60") connecting the narrow end (50, 75) and the wide end (40), the edge-wall (60, 62, 60") being a light reflective surface reflecting light from the light source (20, 75) towards the wide end (40), wherein the reflective surface is made of one material and exhibits light reflective property having a non-zero diffusing component and a non-zero specular component, the specular component being at least 10% of the total reflection when the incident light is at 30° to the reflective surface.

2. Illumination system (10, 12, 14, 16) as claimed in claim 1, further comprising a diffusing element (75) extending across the tapered reflector (30, 32) to separate the tapered reflector in two parts: an upper reflector (70) comprising said narrow end (50) and a lower reflector (90) comprising said wide end (40).

3. Illumination system (10, 12, 14, 16) as claimed in claim 2, the tapered shape of the upper reflector is designed to mix the light emitted by the light source and the tapered shape of the lower reflector is designed to collimate the light outputting the wide end (40).

4. Illumination system (10, 12, 14, 16) as claimed in claim 3, the angle of the tapered wall of the upper reflector with respect to a main optical axis is lower than the angle of the tapered wall of the lower reflector with respect to this main optical axis.

5. Illumination system (10, 12, 14, 16) as claimed in claim 1, wherein the geometry of the tapered reflector for a determinate wide edge opening is given by:

2H/(w+d)=sqrt(2)/tan b where H is the reflector height, w is the longest side of the wide end, d is the longest side of the diffusing element, and b is the screening angle of the reflector.

6. Illumination system (10, 12, 14, 16) as claimed in claim 1, wherein the reflective surface is continuous, without optical breaks.

7. Illumination system (10, 12, 14, 16) as claimed in claim 1, wherein the tapered reflector is made integral. 8. Illumination system (10, 12, 14, 16) as claimed in claim 1, wherein the reflective surface is made of a white plastic, polished until obtaining a desired specular component.

9. Luminaire (100, 102) comprising the illumination system (10, 12, 14, 16) as claimed in any of the claims 1 to 9, and at least a first illumination system (10, 12, 14, 16) having a first beam-shape (80) and comprising at least a second illumination system (10, 12, 14, 16) having a second beam-shape (82), different from the first beam shape (80).

10. Luminaire (100, 102) as claimed in claim 9, wherein the first illumination system (10, 12, 14, 16) comprises a first edge-wall (60) and the second illumination system (10, 12, 14, 16) comprises a second edge-wall (62), a curvature of the first edge-wall (60) being different compared to a curvature of the second edge-wall (62).

11. Luminaire (100, 102) as claimed in claim 9 or 10, wherein the luminaire (100, 102) comprises a controller (110) for controlling the first illumination system (10, 12, 14, 16) independent from the second illumination system (10, 12, 14, 16).

12. Luminaire (100, 102) as claimed in claim 11, wherein the controller (110) is configured for controlling a curvature of the first edge-wall (60) and/or for controlling a curvature of the second edge-wall (62).

13. Luminaire (100, 102) as claimed in claim 11 or 12, wherein the controller (110) is configured for controlling an intensity of the first illumination system (10, 12, 14, 16) and/or of the second illumination system (10, 12, 14, 16).

14. Backlighting system (100, 102) comprising the illumination system (10, 12,

14, 16) according to claim 1, or comprising the luminaire (100, 102) as claimed in claim 9.

Description:
Illumination system and luminaire

FIELD OF THE INVENTION

The invention relates to an illumination system comprising a light source and a tapered reflector.

The invention also relates to a luminaire comprising the illumination system according to the invention.

BACKGROUND OF THE INVENTION

Such illumination systems are known per se. They are used, inter alia, in luminaires for general lighting purposes, for example, for office lights, for shop lights or, for example, for shop window lights.

Typically, luminaires for illuminating public places and, for example, for use in offices have to comply with the glare regulations. Glare results from excessive contrast between bright and dark areas in the field of view. Glare can, for example, result from directly viewing a filament of an unshielded or badly shielded light source. Especially when using LEDs, direct view into the LEDs by a user near the luminaire should be prevented to reduce the glare of the luminaire and to increase the visual comfort of the user. To prevent glare, a normalized luminance profile is defined in, for example, the European EN 12464-1 norm which dictates that the emission of light should not exceed a luminance of 1000 cd/m 2 at viewing angles above 65 degrees.

Different optical constructions are employed to limit glare. In fluorescent light sources, louvers are often used to limit glare. Although the use of louvers enable to create a well-defined beam shape and low glare, they can substantially only be employed in combination with light sources having a relatively low brightness such as fluorescent light sources. A more recent optical construction for limiting glare is by using prismatic sheets or plates. Such prismatic sheets or plates - for example, commercially distributed by the applicant under the commercial name MLO, or MicroLens Optics - may be used in combination with both fluorescent light sources and light sources having higher brightness, such as light emitting diodes (further also indicated as LED). A disadvantage of the known prismatic sheets is their limited beam-shape control. SUMMARY OF THE INVENTION

It is an object of the invention to provide an illumination system having improved beam-shape control while maintaining relatively low glare.

According to the first embodiment of a first aspect of the invention the object is achieved with an illumination system claimed in claim 1. According to a second aspect of the invention, the object is achieved with a luminaire as claimed in claim 10. According to a third aspect of the invention, the object is achieved with a backlighting system as claimed in claim 15.

The illumination system according to the first aspect of the invention comprises a light source and a tapered reflector. The light source comprises a light-emitting surface being arrange at a narrow end of the tapered reflector and may have a dimension substantially equal to a dimension of the narrow end of the tapered reflector, and may be arranged for emitting substantially diffuse light towards a wide end of the tapered reflector. The tapered reflector comprising an edge-wall connecting the narrow end and the wide end in which the edge-wall being a reflective surface reflecting light from the light source towards the wide end.

The symmetry axis of the tapered reflector is typically arranged from a center of the narrow end to a center of the wide end and, for example, coincides with the optical axis of the illumination system. The symmetry axis intersects an imaginary surface which coincides with an edge of the tapered reflector at the wide end and/or the narrow end, the intersection between the symmetry axis and the imaginary surface may, for example, be substantially perpendicular. The tapered reflector may comprise a truncated cone-shape or a truncated pyramid-shape or any differently shaped tapered reflector. The intersection between the edge of the wide end and/or narrow end and the imaginary surface may be circular, elliptical and polygonal. Especially tapered reflectors having a shape of the intersection being elliptical or rectangular may be very useful in street lighting in which a relatively wide light beam is required parallel to the street and a relatively narrow beam is required perpendicular to the street. The tapered reflector according to the invention may also be indicated as a concave reflector, and may be embodied with or without neck at its narrow end, the narrow end may be open or closed in which latter embodiment the tapered reflector is a concave reflector cup. The glare value is a value representing the level of glare being a luminance at a viewing angle at 65 degrees.

The tapered shape of the reflector shapes the light as a tapered beam whose sides relate to the wide edge, and limits the surface to illuminate to an area having limits corresponding to the wide edge. The wide edge of the tapered reflector is indeed a light cutoff of the light directly transmitted from the light source and reflected onto the reflective surface of the tapered reflector. Now, the luminance at the limits of the tapered beam and of the surface to illuminate needs to be controlled, especially to comply with lighting regulations. Moreover, efficiency of the lighting intensity needs to be optimized.

These purposes may be found by shaping and sizing the tapered reflector. Inventors propose a specific shaping and sizing of the tapered reflector, according to an embodiment of the invention (see the "second embodiment" of the invention described hereafter).

Inventors have also found that the reflective properties of the reflective surface of the tapered reflector can be also tailored to comply with such regulations or to facilitate the compliance with such regulations. In particular, inventors proposed to provide, according to a first embodiment of the invention, reflective surface made of one material and exhibiting light reflective property having a non-zero diffusing component and a non-zero specular component. The specular component may be at least 10% of the total reflection when the incident light is at 30° to the reflective surface., the specular component being at least 10% or at least 11% of the total reflection when the incident light is at 30° to the reflective surface. As an alternative or a combination, the specular component may be chosen as being at least 5% of the total reflection when the incident light is at 90° to the reflective surface, at least 6% of the total reflection when the incident light is at 60°, 70° or 80° to the reflective surface, at least 7.5% or at least 8.0% of the total reflection when the incident light is at 40° to the reflective surface, and/or at least 15 %, at least 16 %, at least 17% or 18% of the total reflection when the incident light is at 20° to the reflective surface.

The tapered shape of the reflector allows that significant amount of emitted light rays are directed to the reflective surfaces at relative small incident angles, and therefore to be specularly reflected rather than diffusely reflected, due to the particular reflective property of these reflective surfaces according to the invention. This should decrease the glare effect, especially at the light cut-off angles (i.e. angles, with respect to the main axis of the tapered reflector, corresponding to the non-reflected light rays passing close to the wide edge of the reflector), due to the diffusion (as explained hereunder). As a consequence, by adapting the dimensions and shapes of the reflector - and especially the slope(s) of the edge- wall and the height of the reflector, the size of the light source and the part of specularity in the reflective surface, the lighting intensity and shape and glare effect of the light output from the illumination system can be tailored. In particular, the reflectivity according to the invention can contribute to redirect a part of the light rays which would cause glare otherwise. And especially to comply with the lighting regulations - especially around and above 65° - without any accessories.

Furthermore, the possibility to increase the specular reflection allows to increase the lighting efficiency of the illumination system (as explained hereunder).

A particular method to define the specular component is to polish a reflective surface of the reflector, initially entirely diffusive, or the mould of this reflector, until the reflective surface is sufficiently specular, or to provide a mould having a particular rugositiy, homogeneous or heerogeneous. The reflective surface may be made of any injected white plastic.

A reflector fully diffuse would be useful to smooth said light cut-off which would exhibit too much contrasts otherwise.

But, due to the diffusion (and corresponding mutiple reflections), the optical efficiency is not optimised.

Moreover the glare (and so luminance) with such a diffuse surface is also higher, especially at the light cut-off: in a diffuse reflector, light is indeed emitted at all directions, according to the lambertian distribution 1(a) = 1(0) * cos(a) - where I is the illuminance and a is the maximum angle of the beam with respect to the main optical axis of the reflector. Given an orientation of the reflecting surface at 52° (with repect to the main axis of the tapered reflector) the maximum of intensity emitted by a fully diffuse reflector would be located at about 38° (with repect to the main axis of the tapered reflector), and it was thus deduced that the local contribution of a lambertian surface to the glare directions is 25% of the total reflected light near to the reflector wide edges, and diminishes by approaching the said main axis, since more light is reflected towards the opposite side of the reflector.

Therefore, with a fully diffuse reflective surface, one needs to screen more than only the source by increasing the height of the reflector.

By providing a specular component in this reflective surface, internal light reflection in the system is reduced (due to less multiple reflections), and the optical efficiency is accordingly improved and the height of the reflector can therefore be reduced.

On the contrary, a reflective surface entirely specular is typically obtained with a metallic coating provided onto the inner walls of a reflector. Since the reflective surface according to the invention can be obtained by the direct surface of the inner walls of the reflector the invention prevents from performing this coating and the manufacturing is therefore more cost-effective.

Moreover the inventors have surprisingly observed that such reflective surface exhibits a substantial optical efficiency which is close to those of a fully metallic specular reflector with a sufficient glare reduction to comply with the regulations.

Moreover, the reflectivity on a reflective surface entirely specular is less important (87% found from measurement done by the inventors from an coated Aluminium surface) than a reflective surface of the invention (95% found from measurement done by the inventors from a similar illumination system having injected plastic edge walls ). So a specular finishing on a 3D surface is less reflective than a well polished injected reflector.

A further effect of the illumination system according to the first embodiment invention is that the solution for generating an illumination system complying with the glare- requirements is relatively cost-effective. Often, in known illumination system, prismatic plates/sheets are used to limit the glare value. Such prismatic sheets are relatively expensive and the applying of prismatic sheets in the known illumination systems is relatively expensive. Also the placement of louvers for limiting the glare for, for example, fluorescent light sources, is relatively time-consuming and thus relatively expensive. The tapered reflector may be relatively cost-effectively produced, for example, from plastics which are shaped via, for example, injection-molding or plastics-deformation processes. After applying a layer to the edge-wall generating said reflecting edge-wall, the tapered reflector may be arranged around the light source for generating the illumination system having limited glare value at relatively low cost.

A shape of the light-beam as emitted by the illumination system depends on, amongst other, the shape of the tapered reflector and the specular component used for the reflective surface of the tapered reflector. A shape of the tapered reflector which generates a specific predefined beam shape may be determined via the use of, for example, optical modeling software, also known as ray-tracing programs, such as LightTools ® .

Preferably, the illumination system according to the first embodiment of the invention, further comprises a diffusing element extending across the tapered reflector to separate the tapered reflector in two parts: an upper reflector comprising said narrow end and a lower reflector comprising said wide end.

Advantageaously, the upper reflector may be designed as a cavity to mix the light emitted by the light source and the lower reflector may be designed to shape or collimate, by reflection, the light coming from the upper reflector through the diffusing element. For example, the angle of the tapered wall of the upper reflector with respect to a main optical axis is lower than the angle of the tapered wall of the lower reflector with respect to this main optical axis (or the main axis of the tapered reflector) to increase the optical efficiency of this cavity.

The upper reflector solves accordingly a problem of source luminance, while the lower reflector reduces the luminance at high angles.

Additionally, the use in the lower reflector of controlled specular and diffuse reflection allows to optimally redirect only the light components that would cause glare. Therefore the reflective surface according to the invention allows to refine the brightness reduction obtained with the diffusing element but reducing the glare at critical angles with respect to the main optical axis (e.g. 65°, according to the regulations), to increase sustantially the light efficiency and to smooth the light cut-off effects. Unpleasant effects are therefore withdrawn while otpimising the emitted light energy. Moreover the invention allows to comply with any kinds of regulations by simply adjusting the specular component of the reflective surface and the shape of the reflector, needless of additional optical accessories.

Optionally, the lower reflector may be optically in contact with the lower reflector to avoid any optical loss. In particular, the two levels (upper and lower reflctors) are realized in a single part. As a consequence the light losses due to gaps and other imperfections are minimized. Additionally, this allows to reduce assembly costs.

Optionally, the diffusing element comprises diffuse scattering means for diffusely scattering the light from the light emitter. Due to such diffuse scattering means, the brightness of the light source is reduced to prevent users from being blinded by the light when looking into the illumination system. The diffuse scattering means may be a diffuser plate, diffuser sheet or a diffuser foil.

In particular, the diffusing element may comprise holographic scattering structures for diffusely scattering the light from the light emitter. An efficiency of holographic scattering structures is much higher compared to other known scattering elements allowing the emission of diffuse light from the light source while maintaining a relatively high efficiency of the light source. The high efficiency is typically due to the relatively low back-scattering of the holographic scattering structure.

The diffusing element may comprise embedded luminescent material for converting light emitted by the light source into light of a longer wavelength. The luminescent material may be beneficially used to adapt a color of the light emitted by the illumination system by converting light emitted by the light source into light of a different color. When, for example, the light source emits ultraviolet light, the diffusing element may comprise a mixture of luminescent materials which each absorb ultraviolet light and convert the ultraviolet light into visible light. The specific mixture of luminescent materials, when mixed, provides a mixture of light with a predefined perceived color. Alternatively, the light source emits visible light, for example, blue-light and part of the blue-light is converted by luminescent material into light of a larger wavelength, for example, yellow-light. When mixed with the remainder of the blue-light, light of a predefined color, for example, white- light may be generated.

Alternatively to the previous example, luminescent material may be applied onto a surface of the diffusing element for converting light emitted by the light emitter into light of a longer wavelength. Especially when applying the luminescent material to a surface of the diffusing element facing the light source, the layer of luminescent material is not immediately visible from the outside of the illumination system. In the example, in which the light source emits blue-light of which a part of the blue-light is converted by the luminescent material into yellow-light, the luminescent material performing this conversion is perceived as yellow. When the luminescent material is visible from the outside of the illumination system, the sight of this yellow luminescent material (which may, for example, be the luminescent material: YAG:Ce) may not be preferred by a manufacturer of the illumination system as it may confuse users of the illumination system in thinking the illumination system emits yellow light. As such, when applying the luminescent material at the surface of the scattering element facing towards the light source, the luminescent material is not directly visible from the outside, reducing the yellow appearance of the diffusing element and as such reducing the confusion to users of the illumination system.

Optionally, the geometry of the tapered lower reflector for a determinate wide end opening is given by:

2H/(w+d)=sqrt(2)/tan b

where H is the reflector height, w is the longest side of the wide end, d is the longest side of the diffusing element, and b is the screening angle (i.e. the largest angle between (i) the main axis of the tapered reflector and (ii) a line passing through a point of the wide edge of the reflector and the interesction between the main axis and the diffusing element). It allows to determine the geometry of the reflector needed to screen the source. The source needs to be screened to prevent glare. One method of design would be to fix first the width ("w") of the wide end and the diffusing element dimensions ("d") - which can be considered as a virtual light source - and then to adapt height and reflective properties of the tapered reflector.

In an embodiment of the illumination system, the light source comprises an organic or inorganic light emitting diode emitting light across a surface substantially equal to the light-emitting surface. A benefit when using the organic light emitting diode as light source is that these organic light emitting diode typically already emit substantially diffuse light uniformly across the light-emitting surface of the organic light emitting diode. As such, no additional measures are required to provide uniform illumination of the narrow end of the reflector. Furthermore, because organic light emitting diodes typically are relatively thin, the overall height of the illumination system may be smaller compared to illumination systems having a different light source.

In an embodiment of the illumination system the light source comprises a light emitter and a scattering element comprising the light-emitting surface, the light emitter being configured for substantially evenly illuminating the scattering element. A benefit of this embodiment is that the combination of the light-emitter and the scattering element allows choosing the level of diffusion of the light emitted by the light source. As the scattering element may be chosen, the level of scattering may be adapted by, for example, replacing one scattering element with another. The use of different scattering elements allows an optical designer to adapt, for example, the minimum height of the tapered reflector.

The illumination system according to the invention may also share a light emitter with a further illumination system. When, for example, the illumination system is arranged in an array of illumination systems, each illumination system may comprise the scattering element and a light emitter may be arranged to illuminate a plurality of scattering elements of a plurality of illumination systems. In such an arrangement, the light emitter may be located at sufficient distance from the plurality of scattering elements to ensure a uniform illumination of the scattering elements.

In an embodiment of the illumination system, the light-emitting surface of the light source is convexly shaped towards the wide end of the tapered reflector. A benefit of such convexly shaped light-emitting surfaces is that these light-emitting surfaces may be more uniformly lit by a light source having, for example, a Lambertian light distribution, for example, light emitting diodes. Such improved uniformity further reduces the brightness of the diffuse light emitted by the light source, further reducing the glare. A further benefit of the convexly shaped light-emitting surface is that it allows room for the light emitter which eases the manufacturing of the illumination system according to the invention. When the light emitter is, for example, a light emitting diode, the light emitting diode is typically applied to a circuit-board such as a PCB. This PCB may be used to fix both the tapered reflector and the convexly shaped light-emitting surface, improving the ease of manufacturing the illumination system. In addition, the convexly shaped light-emitting surface may provide space for driver electronics for the light emitter.

In an embodiment of the illumination system, the edge-wall is curved inward towards the symmetry axis of the tapered reflector for adapting a beam shape of the light emitted by the illumination system. A benefit of this inwardly curved edge-wall is that the glare value at 65 degrees is significantly decreased. This reduced glare value allows installing a higher light flux in the illumination system having inwardly curved edge-walls compared to the substantially straight edge-wall while maintaining within the glare norm. The exact curvature required of the edge-wall may be depending on the shape and size of the light- emitting surface of the light source and may be determined using, for example, the optical modeling software, also known as ray-tracing programs, such as ASAP ® , lighttools ® , etc.

In an embodiment of the illumination system, the illumination system comprises curvature-means for adapting a curvature of the edge-wall. Such curvature means may, for example, manually or automatically adapt the curvature of the edge-wall to adapt the beam-shape of the light emitted by the illumination system. As such, the illumination system according to the invention may be configured to emit different beam-shapes depending on the adaptation by the curvature-means.

In an embodiment of the illumination system, the curvature-means are configured for adapting the height of the tapered reflector for adapting the curvature of the edge-wall. Because the glare value is substantially constant for different heights of the tapered reflector, the adaptation of the height may be used to alter a curvature of the edge- wall to adapt the beam-shape. The edge-wall may be manufactured of deformable material, for example, a white rubber like component. Alternatively or in combination the edge-wall may be covered with a high gloss white coating(which reflectance can be described by a diffuse (e.g. Lambertian) contribution and a specular component defined at the top of the coating. Adapting the height of the tapered reflector, for example, manually or via motor- control, the deformable material deforms which adapts a shape of the edge-wall to alter the beam-shape as emitted by the illumination system. As such, an adaptable illumination system in which the beam shape may be adapted is obtained. According to a second embodiment of the invention, which can be taken alone or in combination with any feature of said first embodiment of the invention, the height of the tapered reflector is a dimension measured substantially parallel to a symmetry-axis of the tapered reflector, and the height of the tapered reflector is selected to be equal or larger than a minimum height which is a lowest height-value in a range of height-values of the tapered reflector. In the range of height-values a glare value of the illumination system remains substantially constant.

The edge wall of the tapered reflector comprises diffusely reflecting material which may be fully diffusive, according to for example a white, diffuse reflecting material, typically having a reflectivity of 95% to 98%. Alternatively, the edge wall may have the reflective property according to the first embodiment (i.e. having a diffusive and a specular component).

An effect of the illumination system according to this second embodiment is that the combination of the light source emitting substantially diffuse light together with the tapered reflector generates an illumination system in which a shape of a beam of light emitted by the illumination system may be adapted while maintaining a relatively low glare value. Inventors have found that the illumination system according to the invention has a specific behavior with respect to glare: at a height above the minimum height, the glare value remains substantially constant over a relatively large range of height- values. Without wishing to be held to any particular theory, the inventors believe that this behavior is due to the combination of the diffuse light emitted by the light source having the light-emitting surface of the first dimension and to the diffuse reflecting edge-wall of the tapered reflector. This typical combination generates this specific behavior in which the glare value of the illumination system at and above a specific minimum height of the tapered reflector does not seem to change significantly when increasing the height. At a height of the tapered reflector below the minimum height, the glare value as measured from the illumination system reduces with increasing height of the tapered reflector - as expected. However, this expected behavior changes at or near the minimum height. Altering the height of the tapered reflector within the range of height-values does not change the glare value significantly. Still, increasing the height of the tapered reflector does typically alter a shape of a light-beam emitted by the illumination system. As such, an illumination system is designed in which the beam-shape may be altered without significantly affecting the glare value of the illumination system. Known prismatic optical plates which are used to limit the glare in known illumination systems only are capable of generating a single beam-shape at a single glare value. Adapting the known prismatic optical plate may adapt the beam-shape, but typically also increases the glare value of the system. As such, in the known prismatic optical plates, only a single beam- shape seems to be possible at one glare value. Using the illumination system according to the invention enables multiple beam shapes while substantially maintaining the glare value of the illumination system constant. Such an illumination system provides a very interesting design feature which may be used to design a specific required illumination distribution and aesthetics while maintaining substantially constant, low glare value.

A further effect when using the illumination system according to this second embodiment is that the minimum height within the range of height- values having substantial constant glare often substantially coincides with a glare value minimum of the illumination system. The amount of flux which may be installed per illumination system is determined by the glare value which is just acceptable in illumination systems according to normalized emission profiles. Due to the fact that the range of substantially constant glare value is found at or near a glare value minimum of the illumination system, the maximum light flux may be installed at the illumination system according to the invention while the glare value within the range of height-values remains within the defined normalized emission profile. As such, the illumination system according to the invention may be designed to provide a maximum flux of light while maintaining the glare value of the illumination system within the predefined glare-level and offering designers to generate a specific required illumination distribution via shaping the light-beam emitted from the illumination system.

A further effect of the illumination system according to the invention is that the solution for generating an illumination system complying with the glare-requirements is relatively cost-effective. Often, in known illumination system, prismatic plates/sheets are used to limit the glare value. Such prismatic sheets are relatively expensive and the applying of prismatic sheets in the known illumination systems is relatively expensive. Also the placement of louvers for limiting the glare for, for example, fluorescent light sources, is relatively time-consuming and thus relatively expensive. The tapered reflector may be relatively cost-effectively produced, for example, from plastics which are shaped via, for example, injection-molding or plastics-deformation processes. After applying a layer to the edge-wall generating a diffusely reflecting edge- wall, the tapered reflector may be arranged around the light source for generating the illumination system having limited glare value at relatively low cost.

A shape of the light-beam as emitted by the illumination system depends on, amongst other, the shape of the tapered reflector and possibly the specular component used for the reflective surface of the tapered reflector. A shape of the tapered reflector which generates a specific predefined beam shape may be determined via the use of, for example, optical modeling software, also known as ray-tracing programs, such as LightTools ® .

In an embodiment of the illumination system, the range of height-values comprises height values in which a variation of the glare value within the range of height- values of the tapered reflector is less than 10% of an average glare value within the range of height-values, and/or wherein the range of height-values comprises height values in which the variation of the glare value within the range of height-values of the tapered reflector is less than 5% of the average glare value within the range of height-values. The inventors have found that the glare value remains substantially constant within the range of 10% of the average glare value within a relatively large range of height-values, allowing optical designers a relatively broad range of beam-shapes to generate from the illumination system without exceeding the glare-norm excessively. From experience, the inventors have found that a variation of the glare value of 10% is still acceptable when, for example, applying the illumination system as office lighting for illuminating an office. When the variation of the glare value within the range of height-values is reduced, for example, to less than 5%, the light flux which may be installed in the illumination system may be better optimized and may be closer to the maximum light flux which may be installed without exceeding the glare norm of luminance 1000 (cd/m 2 ) at an angle of 65 degrees. According to a second aspect of the invention, the object is achieved with a luminaire comprising an illumination system according to the invention.

In an embodiment of the luminaire, the luminaire comprises at least a first illumination system having a first beam-shape and comprising at least a second illumination system having a second beam-shape, different from the first beam shape. Having both the first illumination system and the second illumination system in the luminaire enables a user to choose either of the first beam-shape or the second beam- shape or a combination of the first beam-shape and the second beam-shape to be emitted from the luminaire. When, for example, the first beam-shape is especially beneficial for illuminating a surface below the luminaire, while the second beam-shape is especially beneficial for illuminating a wide area around the luminaire, the first beam- shape may be used when requiring light at the surface below the luminaire, for example, a desk or table, while the second beam-shape may be used when an overall illumination of the room is required. A combination of both beam-shapes may allow a general illumination of the room together with a good illuminated desk - typically required by office illumination. The luminaire may comprise a plurality of first illumination systems and a plurality of second illumination systems arranged in a mixed array of first and second illumination systems. Alternatively, the luminaire may comprise a few selected illumination systems of the plurality of illumination system having a different beam-shape to, for example, obtain a specific illumination effect, for example, to illuminate a picture on a wall.

A cross-section perpendicular to the symmetry axis of the illumination system may result in a circular cross-section, elliptical or, for example, a polygonal cross-section. The arrangement of the plurality of illumination systems in the luminaire may be in a two- dimensional array of illumination systems at a close packed arrangement corresponding to the cross-sectional dimensions of the illumination systems.

In an embodiment of the luminaire, the first illumination system comprises a first edge-wall and the second illumination system comprises a second edge-wall, a curvature of the first edge-wall being different compared to a curvature of the second edge-wall. As such, a regular packed arrangement of the plurality of illumination systems may be obtained, while the different curvatures of the edge-walls allows still a different beam-shape of the first illumination system compared to the second illumination system.

In an embodiment of the luminaire, the luminaire comprises a controller for controlling the first illumination system independent from the second illumination system. This controller may simply be a pair of switches with which the set of first illumination systems in the luminaire may be switched independently from the set of second illumination systems, allowing a user to either only switch on the set of first illumination system, to only switch on the set of second illumination systems, or to switch on both sets of first illumination systems and second illumination systems. Alternatively, the controller may comprise dimmers for dimming the set of first illumination systems independent from the set of second illumination systems. Also beam-shape adaptation means may be present to adapt a beam-shape of the first illumination systems from the set of first illumination systems independent from the beam-shape of the second illumination systems from the set of second illumination systems.

In an embodiment of the luminaire, the controller is configured for controlling a curvature of the first edge-wall and/or for controlling a curvature of the second edge-wall. Such a controlling of the curvature of the first edge-wall and/or of the second edge-wall may be a continuous control of the curvature such that substantially any beam-shape may be generated using the controller. In an embodiment of the luminaire, the controller is configured for controlling an intensity of the first illumination system and/or of the second illumination system. This may be achieved via dimmers connected to the first illumination system and the second illumination system which may, for example, be controlled by the controller.

According to a third aspect of the invention, the object is achieved with a backlighting system comprising the illumination system according to the invention, or comprising the luminaire according to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter.

In the drawings:

Fig. 1A shows a schematic cross-sectional view of an illumination system according to the invention, Fig. IB shows a graph indicating the calculated intensity at 65 degrees versus the height for the illumination system of Fig. 1A, and Fig. 1C shows a graph indicating the variation of the beam width with varying the height of the illumination system,

Fig. 2A shows a schematic cross-sectional view of a further embodiment of the illumination system according to the invention, Fig. 2B shows a graph indicating the calculated intensity at 65 degrees versus the height for the illumination system of Fig. 2A,

Fig. 3 shows a graph indicating the beam shape of two different illumination systems according to the invention,

Figs. 4A and 4B show different embodiments of a luminaire according to the invention.

FIG. 5 is a longitudinal cross-section view of an illumination system according to another embodiment of the invention, wherein the illumination comprising an upper and a lower reflector, separated by a diffusing element extending across the reflector.

FIG. 6 is a graph of luminances obtained at various azimuthal angles with respect to the main optical axis A of FIG. 5, for an illumination system having a fully diffusive reflective surface, a reflective surface according to the invention and a fully specular reflective surface.

FIG. 7 is a part of the graph of FIG. 6 around 65°.

FIG. 8 is a graph of the intensity of the light reflected by a reflective surface according to the invention, at different angular incidences of the light. The figures are purely diagrammatic and not drawn to scale. Particularly for clarity, some dimensions are exaggerated strongly. Similar components in the figures are denoted by the same reference numerals as much as possible. DETAILED DESCRIPTION OF EMBODIMENTS

1 st embodiment of the invention

Fig. 5 shows a schematic cross-sectional view of an illumination system 10 according to the invention. The illumination system 10 comprises a light source 80 and a tapered reflector 30. The light source comprises a light-emitting surface 21 which has a dimension substantially similar to a dimension of a narrow end 50 of the tapered reflector 30, emitting substantially light, optionally diffuse, towards a wide end 40 of the tapered reflector 30. The tapered reflector 30 comprises an edge wall 60 which connects the narrow end 50 with the wide end 40. The tapered reflector 30 has a height which is a dimension of the tapered reflector 30 in a direction substantially parallel to a symmetry-axis A of the tapered reflector 30.

The illumination system 10 further comprises a diffusing element 75 extending across the tapered reflector 30 to separate the tapered reflector 30 in two parts: an upper reflector 70 comprising said narrow end 50 and a lower reflector 90 comprising said wide end 40. The upper reflector 70 is designed to mix the light emitted by the light source 80 and the lower reflector 90 is designed to shape or collimate, by reflection, the light coming from the upper reflector 70 through the diffusing element 75. As depicted in FIG. 5, the angle of the tapered wall 60' of the upper reflector 70 with respect to the main optical axis A is lower than the angle of the tapered wall 60" of the lower reflector 90 with respect to the main optical axis A, so as to facilitate, respectively, said mixing and said collimation.

The reflectivity of the inner reflective surface of the tapered walls 60' and 60" has a diffusive component and a specular component, the specular component being at least 5 % of the total reflection when the incident light is perpendicular to the reflective surface and at least 50% of the total reflection when the incident light is at 5° to the reflective surface.

- FIG. 8 shows the angular distributions of intensities of lights reflected on a reflective surface, for the following different incident angles (with respect to the reflective surface): Curve (a): incidence angle = 20°

Curve (b): incidence angle = 30°

Curve (c): incidence angle = 40° Curve (d): incidence angle = 50°

Curve (e): incidence angle = 60°

Curve (f): incidence angle = 70°

Curve (g): incidence angle = 80°

Curve (h): incidence angle = 90°

The material used which was GEPAX 8000, and the reflector was thermo formed with the following features:

"w"= 130mm

"d"=35mm

"H" =64.8mm

"b" = 60°

The mould had been polished to have a mean rugosity RA lower than 0.4 micrometer.

Graph of FIG. 8 shows that high specular reflectivity results in a high peak, while the diffuse part is a flat curve.

Indeed, the part of the graph referenced "4" shows the part of the diffuse light in the reflected light, and that this diffused reflected light is nearly the same whatever the angle of measurement is. Moreover, smaller incident light, smaller the diffusive reflectivity (not shown in FIG. 8).

On the contrary, the peaks show that smaller incident angle, greater the specular reflectivity.

Table below shows in details the diffusive and specular components in the reflected light, as measured by the inventors at different incident angles with respect to the reflective surface.

Angle (°) R(diffuse) R(specular) %age of R(specular)

20 74.8 17.2 18.7 %

30 81.5 10.5 11.4 %

40 84.5 7.5 8.1 %

50 85.8 6.2 6.7 %

60 86.3 5.7 6.2 %

70 86.4 5.6 6.1 %

80 86.4 5.6 6.1 %

90 87.4 4.6 5.0 % Moreover, FIG. 6 shows that the comparison between the luminance of a full diffusive reflective surface (curve 1), a partly specular and partly diffuse reflective surface (same reflector as for FIG. 8) (curve 2), and a full specular reflective surface (curve 3) for the same geometrical and dimensional lighting installation of FIG. 5. If the optical efficiency is clearly lower for the full diffuse reflective surface than the two other types of reflective surfaces, this efficiency of the reflective surface of the invention and of the fully specular reflective surface is similar.

Moreover, FIG. 7 shows the parts of the curves 1 , 2, 3 of FIG. 6 around the light cut-off 65°. It can be noticed that the glare is maximum for the full diffuse reflective surface, reduced for the reflective surface of the invention and close to zero for the fully specular reflective surface. Nevertheless, the light contrast of the fully specular reflective surface is quite high at the light cut-off (especially around 60°) which gives an unpleasant lighting drop on the surface to illuminate. On contrary, the reflective surface of the invention smoothes this light cut-off (and therefore smoothes the contrast), a bit less than the fully diffuse reflective surface.

Therefore the reflective surface according to the invention allows to reach a high optical efficiency, glare reduction sufficient to comply with the regulations and a sufficient light smoothing at the light cut-off.

Moreover, the specular component of the reflective surface of the edge walls 60'-60" of the tapered reflector 30 can be adjusted, according to the desired lighting effects to be obtained and also according to the size and shape, geometry of the tapered reflector 30. For example the reflector finishing can be uniform but can also be locally adjusted. For example, to create asymmetric beams the reflectivity of one side of the reflector can be different from the other side.

The lower reflector 90 is advantageously optically in contact with the lower reflector 70 to avoid any optical loss. In particular, the two levels (upper and lower reflctors 70-90) are preferably realized in a single part, optionally integrally made. The edge walls 60' and 60" may be made of a unique plastic material, preferably white-type to reach a high reflectivity (which is typically greater than 90%, or more preferably greater than 95% for such type of material), injected in a mould. One method of fabrication of the reflective surface may be to provide first a mould having inner surfaces having rugosity or other elements arranged to provide a fully diffuse reflective surface after injection, from which a polishing step is performed so as to smooth more or less these inner surfaces: more polished the inner surfaces, more specular the reflective surfaces. Alternatively or incombination of this method of fabrication, a step of polishing may also be performed directly on the reflective surfaces of the edge walls 60'-60".

The diffusing element 75 may comprise diffuse scattering means for diffusely scattering the light from the light source 80. The diffuse scattering means may be a diffuser plate, diffuser sheet or a diffuser foil 75.

In particular, the diffusing element 75 may comprise holographic scattering structures for diffusely scattering the light from the light emitter.

The diffusing element 75 may comprise embedded luminescent material for converting light emitted by the light source 80 into light of a longer wavelength. The luminescent material may be beneficially used to adapt a color of the light emitted by the illumination system 10 by converting light emitted by the light source 80 into light of a different color. When, for example, the light source 80 emits ultraviolet light, the diffusing element 75 may comprise a mixture of luminescent materials which each absorb ultraviolet light and convert the ultraviolet light into visible light. The specific mixture of luminescent materials, when mixed, provides a mixture of light with a predefined perceived color. Alternatively, the light source 80 emits visible light, for example, blue-light and part of the blue-light is converted by luminescent material into light of a larger wavelength, for example, yellow-light. When mixed with the remainder of the blue-light, light of a predefined color, for example, white-light may be generated.

Alternatively to the previous example, luminescent material may be applied onto a surface of the diffusing element 75 for converting the light emitted by the light emitter into light of a longer wavelength. Especially when applying the luminescent material to a surface of the diffusing element 75 facing the light source 80, the layer of luminescent material is applied so as not to be immediately visible from the outside of the illumination system 10.

Optionally, the geometry of the tapered lower reflector for a determinate wide end opening is given by:

2H/(w+d)=sqrt(2)/tan b

The illumination system 10 may also comprise means for mounting the diffusing element 75 to the tapered reflector 30, this means being arranged to not interfere with the transmitted and reflected light.

As a consequence, the light leakage is therefore minimized and the corresponding efficiency drop due to the fixation of this diffusing element 75 into the tapered reflector 30 is also minimized. 2" embodiment of the invention

Fig. 1A shows a schematic cross-sectional view of an illumination system 10 according to the invention. The illumination system 10 comprises a light source 20 and a tapered reflector 30. The light source comprises a light-emitting surface 21 which has a dimension substantially identical to a dimension of a narrow end 50 of the tapered reflector 30, emitting substantially diffuse light towards a wide end 40 of the tapered reflector 30. The tapered reflector 30 comprises an edge wall 60 which connects the narrow end 50 with the wide end 40. An inner wall of the tapered reflector 30 may be covered with a white, diffuse reflecting material, for example, having a reflectivity of 95% to 98%, with or without the specular component already discussed in the first embodiment. The tapered reflector 30 has a height h which is a dimension of the tapered reflector 30 in a direction substantially parallel to a symmetry-axis A of the tapered reflector 30.

Fig. IB shows a graph indicating the calculated intensity at 65 degrees. This intensity value may be converted into a luminance and glare value versus the height h for the illumination system of Fig. 1A. The calculations to generate Fig. IB have been carried out at constant dimensions of the wide end dw and the narrow end dn of the tapered reflector 30. Only the height h of the tapered reflector 30 is varied. Inventors have found that the illumination system 10 as shown in Fig. 1A has a specific behavior with respect to glare: at a height h above a minimum height hmin (indicated in the graph), the glare value hardly changes. Without wishing to be held to any particular theory, the inventors believe that this behavior is due to the combination of the diffuse light emitted by the light source 20 having the light-emitting surface 21 and to the diffuse reflecting edge-wall 60 of the tapered reflector 30. This typical combination generates this specific behavior in which the glare value of the illumination system 10 at and above a specific minimum height hmin of the tapered reflector 30 does not seem to change significantly when increasing the height h. The graph shown in Fig. IB is a result of a simulation using modeling software in which zero optical loss is assumed (a wall reflectivity of 100%) is assumed. In practice, a wall reflectivity of 95% to 98% is typical. However, for relatively long tapered reflector cavities 30, an appreciable optical loss may be expected.

In general, a relatively small light source filling the relatively small narrow end dn is beneficial to obtain relatively low glare value. However, such a small light source typically is a too bright light source to look into and would provide visual discomfort to a user. As can be seen from Fig. IB, at the height h of the tapered reflector 10 below the minimum height hmin, the glare value as measured from the illumination system 10 as shown in Fig. 1A reduces with increasing height h - as expected. However, this expected behavior changes at or near the minimum height hmin where the glare value of the illumination system 10 according to the invention is at its minimum or near its minimum value. Altering the height h of the tapered reflector 30 within the range of height-values does not change the glare value significantly. However, although the glare value is substantially constant at a height h above the minimum height hmin, still a shape of a light-beam emitted by the illumination system 10 does change (see also Figs. 2A to 2C). As such, using the illumination system 10 as shown in Fig. 1A the beam-shape may be altered without altering the glare value.

Within the range of height-values, the glare value may, for example, vary less than 10% of an average glare Ga as indicated in graph of Fig. IB. Choosing, for example, a different shape of the edge-wall 62 (see Fig. 2A and 2B) may further reduce the variation of the glare value across the range of height-values to less than 5% of the average glare Ga (see, for example, Fig. 2B). Because in these calculations, no losses are taken into account, the increase of the glare value at large heights as shown in Fig. IB (above 40 mm) will be smaller than is shown in Fig. IB.

As can be seen from Fig. IB, the glare value within the range of height-values having substantial constant glare value substantially coincides with a glare value minimum of the illumination system 10. This allows light-designers to install a maximum light flux in which the resulting glare is at or just below the maximum acceptable glare value as defined in the European EN12464-1 norm. As such, the illumination system 10 as shown in Fig. 1A may be designed to provide a maximum flux of light while maintaining the glare value of the illumination system 10 below the predefined glare-level and offering designers to generate a specific required illumination distribution via shaping the light-beam emitted from the illumination system 10.

The tapered reflector 30 may be produced relatively cost-effectively, for example, from plastics which are shaped via, for example, injection-molding or plastics- deformation processes. After applying a layer to the edge-wall generating a diffusely reflecting edge-wall, the tapered reflector 30 may be arranged around the light source 20 for generating the illumination system 10 having limited glare value at relatively low cost.

In the embodiment of the illumination system 10 as shown in Fig. 1A, the light source 20 is an organic light emitting diode 22. These organic light emitting diodes 22 typically already emit substantially diffuse light uniformly across the light-emitting surface 21 of the organic light emitting diode 22. As such, no additional measures are required to provide uniform illumination of the narrow end 50 of the tapered reflector 30. Furthermore, because organic light emitting diodes 22 typically are relatively thin, the overall height of the illumination system 10 may be smaller compared to illumination systems having a different light source 20.

In addition, Fig. 1C shows a graph indicating the variation of the beam width with varying height h for the illumination system of Fig. 1A. So again, although the glare value remains substantially constant, the beam shape of the light emitted from the illumination system 10 according to the invention may be adapted significantly. This provides a high degree of flexibility in designing and controlling illumination systems 10, 12, 14, 16 for light designers.

Fig. 2A shows a schematic cross-sectional view of a further embodiment of the illumination system 12 according to the invention. In the embodiment shown in Fig. 2A, the edge-wall 62 of the tapered reflector 32 is curved inwards towards the symmetry axis A. The beam shape which is often preferred has a substantially block-shaped emission distribution in which the center of the emission distribution remains at a substantially constant light intensity having relatively steep edges. Such an emission distribution may be obtained by the inward curvature of the edge-wall 62 of the tapered reflector 32 as shown in Fig. 2A. The exact curvature of the edge-wall 62 required for generating the required emission distribution may be depending on the shape and size of the light-emitting surface 21 of the light source 20 and may be determined using, for example, the optical modeling software, also known as ray-tracing programs, such as ASAP ® , lighttools ® , etc.

The illumination system 12 as shown in Fig. 2A may comprise curvature- means (not shown) for adapting a curvature of the edge-wall 62 and adapt the emission distribution of the illumination system 12. The edge-wall 62 may, for example, be manufactured of deformable material. As such, the curvature-means may, for example, be a ring-shaped element (not shown) arranged at a specific height h around the tapered reflector 62 of which a ring-diameter may be adapted to adapt the curvature of the deformable material. Alternatively, the curvature-means may adapt the distance between the narrow end 50 and the wide end 40 of the tapered reflector 32 to adapt the curvature of the edge-wall 62 to adapt the emission distribution of the light emitted by the illumination system 12. Because the glare value is substantially constant for different heights of the tapered reflector 32, the adaptation of the height h may be used to alter the curvature of the edge-wall 62 to adapt the beam-shape.

The embodiment of the illumination system 12 as shown in Fig. 2A further comprises a light source 20 comprising a light emitter 24 and a scattering element 26. When, for example, the light emitter 24 emits light in a substantially Lambertian light distribution, the scattering element 26 may preferably be a concavely shaped scattering element 26 as shown in Fig. 2A to ensure uniform illumination of the scattering element 26 by the light emitter 24. Alternatively, the scattering element 26 may be a substantially flat sheet or plate of scattering material (not shown) comparable to the light source 20 shown in Fig. 1A, in which case the light emitter 24 is positioned at a specific distance from the flat sheet or plate to ensure uniform illumination of the flat scattering element 26. The combination of the light- emitter 24 and the scattering element 26 may be chosen such that the level of scattering of the light emitted by the light source 20 is within a predefined limit. By choosing a different scattering element 26, the level of scattering may be adapted. Alternatively the light emitter 24 may be used to illuminate a plurality of scattering elements 26 each arranged in their respective illumination system 12. In such an arrangement, the distance between the light emitter 24 and the plurality of scattering elements 26 may be chosen such that the light emitter 24 illuminates each of the scattering elements 26 uniformly.

The scattering element 26 may comprise a diffuse scattering element 26, and/or may, for example, comprise holographic scattering structures for diffusely scattering the light from the light emitter 24. Holographic scattering structures are typically more efficient compared to other known scattering elements allowing relatively high efficiency of the emission of diffuse light from the light source 20.

The scattering element 26 may additionally or alternatively comprises luminescent material (not shown) embedded in the scattering element 26 and/or applied on a surface of the scattering element 26 for converting light emitted by the light emitter 24 into light of a longer wavelength. The luminescent material may be beneficially used to adapt a color of the light emitted by the illumination system 12 by converting light emitted by the light emitter 24 into light of a different color. Luminescent material also often has a light- scattering property which, in combination with the light conversion property may be chosen to efficiently generate diffuse light of a predefined color emitted from the narrow end 50 of the tapered reflector 30, 32 towards the wide end 40. When, for example, the light emitter 24 emits ultraviolet light, the scattering element 26 may comprise a mixture of luminescent materials which each absorb ultraviolet light and convert the ultraviolet light into visible light. The specific mixture of luminescent materials, when mixed, provides a mixture of light with a predefined perceived color. Alternatively, the light emitter 24 emits visible light, for example, blue-light and part of the blue-light is converted by luminescent material into light of a larger wavelength, for example, yellow-light. When mixed with the remainder of the blue-light, light of a predefined color, for example, white-light may be generated.

In an embodiment of the illumination system 12 in which the luminescent material is applied to a surface of the scattering element 26, the luminescent material may beneficially be applied to a surface facing the light emitter 24. Such luminescent material is not immediately visible from the outside of the illumination system 12. When the luminescent material is visible from the outside of the illumination system 12, the perceived color of the light source 20 may deviate from the color of the light emitted by the light source 20. When, for example, the luminescent material converts part of the blue light from the light emitter 24 into yellow light, the perceived color of the luminescent material, when the light source 20 is not in operation, is yellow. However, in operation, the light source 20 emits blue light of which part is converted by the luminescent material into yellow which, in combination, provides the perceived white emitted light. As such, the perceived color of the light source 20 may deviate from the color of the light emitted by the light source 20. When applying the luminescent material as a layer to face the light emitter 24, the luminescent material is not directly visible from the outside, reducing the yellow appearance of the scattering element 26 and as such reducing the confusion to users of the illumination system 12.

Different luminescent materials may be used. For example, when the light emitter 24 emits substantially blue light, part of the blue light may be converted, for example, using Y 3 Al 5 0i 2 :Ce 3+ (further also referred to as YAG:Ce) which converts part of the blue impinging light into yellow light. Choosing a specific density of this luminescent material on or in the scattering element causes a predetermined part of the impinging blue light to be converted into yellow, determining the color of the light emitted by the illumination system 10, 12, 14, 16. The ratio of blue light which is converted by the luminescent material may, for example, be determined by a layer thickness of the luminescent material, or, for example, by a concentration of the YAG:Ce particles distributed in the scattering element 26. Alternatively, for example, CaS:Eu 2+ (further also referred to as CaS:Eu) may be used, which converts part of the blue impinging light into red light. Adding some CaS:Eu to the YAG:Ce may result in white light having an increased color temperature. Alternatively, the light emitter 24, for example, emits ultraviolet light, this ultraviolet light may be converted by the luminescent material into substantially white light. For example a mixture of BaMgAlioOi 7 :Eu 2+ (converting ultraviolet light into blue light), CagMg(Si0 4 ) 4 Cl 2 : Eu 2+ ,Mn 2+ (converting ultraviolet light into green light), and Y 2 0 3 : Eu 3+ ,Bi 3+ (converting ultraviolet light into red light) with different phosphor ratios may be used to choose a color of the light emitted from the illumination system 10, 12, 14, 16 which lies in a range from relatively cold white to warm white, for example between 6500K and 2700K. Other suitable luminescent materials may be used to obtain a required color of the light emitted by the illumination system 10, 12, 14, 16.

Fig. 2B shows a graph indicating the calculated intensity at 65 degrees versus which relates to the calculated glare value versus the height for the illumination system of Fig. 2A. Fig. 2B shows a similar behavior as already elucidated in Fig. IB in that the glare value remains substantially constant above a height h larger than the minimum height hmin. As can be seen from comparison between the graphs of Fig. IB and Fig. 2B is that the variation in glare value around the average glare value Ga is less for the tapered reflector 32 as shown in Fig. 2A compared to the tapered reflector 30 as shown in Fig. 1 A.

Fig. 3 shows a graph indicating the beam shape 80, 82 of two different illumination systems 10, 14 according to the invention. The first illumination system 10 having substantially straight edge-walls 60 connecting the narrow end 50 with the wide end 40 of the tapered reflector 30 is comparable to the illumination system 10 as shown in Fig. 1A. The second illumination system 14 is similar to the first illumination system 10 with the difference that the edge-wall 62 is curved inward comparable to the edge-wall as shown in the embodiment of the illumination system 12 shown in Fig. 2A. In the current embodiments shown in Fig. 3, the height h of the first illumination system 10 is equal to the height h of the second illumination system 14, the dimension dn of the narrow end 50 of the first illumination system 10 is equal to the dimension dn of the narrow end 50 of the second illumination system 14, and the dimension dw of the wide end 40 of the first illumination system 10 is equal to the dimension dw of the wide end 40 of the second illumination system 14. The first illumination system 10 generates a first beam shape 80, and the second illumination system 14 generates a second beam shape 82. This second beam shape 82 has a reduced intensity at and above an angle of 65 degrees which results in a reduced glare value from the second illumination system 14 compared to the first illumination system 10 when installing the same light intensity. Although the difference in the graph of fig. 3 seems relatively small, the difference in intensity at 65 degrees is significant and allows installing 20 to 30% more light flux in the second illumination system 14 before the same glare value is achieved at 65 degrees compared to the first illumination system 10. The shape of the tapered reflector 30, 32 which generates the required predefined beam shape 80, 82 may be determined via the use of, for example, optical modeling software, also known as ray-tracing programs, such as LightTools ® .

Figs. 4A and 4B show only a few embodiments of a luminaire 100, 102 according to the 1 st or 2 nd embodiment of the invention. Many varieties may be designed without departing from the scope of the invention.

In Fig. 4A a substantially square illumination system 16 is shown. The luminaire 100 shown in Fig. 4A comprises a regular array of these square illumination systems 16. This specific shape of the illumination system 16 allows a very efficient filling of the available surface of the luminaire 100 with the respective wide end 40 openings of the respective tapered reflector cavities 30, 32, 36 of the individual illumination systems 16. The luminaire 100 may also comprise a first illumination system 16A and a second illumination system 16B in which the emitted intensity and/or beam shape and/or color may be different compared to the first illumination system 16A. In such an embodiment, the luminaire 100 may comprise a controller 110 (see Fig. 4B) which may be used to control the first illumination system 16A and the second illumination system 16B simultaneously or independently. Having both the first illumination system 16A and the second illumination system 16B in the luminaire 100 enables a user to choose either light emitted by the first illumination system 16A, the second illumination system 16B or a combination of both. When, for example, the first illumination system 16A emits a first beam- shape which is especially beneficial for illuminating a surface below the luminaire (for example, a desk), while the second illumination system 16B emits a second beam- shape which is especially beneficial for illuminating a wide area around the luminaire, the first beam-shape may be used when requiring light at the surface below the luminaire, for example, a desk or table, while the second beam-shape may be used when an overall illumination of the room is required. A combination of both beam-shapes may allow a general illumination of the room together with a good illuminated desk - typically required by office illumination.

The luminaire 100 may comprise a plurality of first illumination systems 16A and a plurality of second illumination systems 16B arranged in a mixed array of first and second illumination systems 16 A, 16B. Alternatively, the luminaire 100 may comprise a few selected illumination systems of the plurality of illumination system having a different beam- shape, for example, to obtain a specific illumination effect, for example, to illuminate a picture on a wall.

In Fig. 4B the illumination system 12 as shown in Figs. 2 A is arranged in an array to form a second embodiment of the luminaire 102. The luminaire 102 comprises several rows of illumination systems 12 in which parallel rows are displaced with respect to the previous row to generate a close packing of the illumination system 12. Also the luminaire 102 shown in Fig. 4B may comprise a first illumination system 12A and a second illumination system 12B in which the emitted intensity and/or beam shape and/or color may be different compared to the first illumination system 12 A. Again the controller 110 is present, for example, to control the first illumination system 12A and the second illumination system 12B simultaneously or independently. Having both the first illumination system 12A and the second illumination system 12B in the luminaire 100 enables a user to choose either of light emitted by the first illumination system 12A, the second illumination system 12B or a combination of both, similar to the embodiment shown in Fig. 4A. Fig. 4B also provides an insight in the different element from which the luminaire 102 may be manufactured. Clearly the illumination system 12 comprises the light emitter 24 and the scattering element 26 which together form the light source 20 arranged on a printed circuit board 122. This assembly is subsequently applied to a rear- wall 120 of the luminaire 102 and fixed with the array 124 of tapered reflector cavities 32 of the individual illumination systems 12. The array 124 of tapered reflector cavities 32 may, for example, be produced in one production step, for example, via a well known injection molding process. As indicated before, the scattering element 26 may comprise luminescent materials for altering or tuning a color of the light emitted by the individual illumination systems 12. Because the assembly is relatively quick and simple allowing relatively known and inexpensive production processes to be used, for example, for the array 124 of tapered reflector cavities 32 allow such luminaire 102 to be relatively cost-effectively produced.

The luminaire 102 may again comprise a plurality of first illumination systems 12A and a plurality of second illumination systems 12B arranged in a mixed array of first and second illumination systems 12 A, 12B. Alternatively, the luminaire 102 may comprise a few selected illumination systems of the plurality of illumination system 12 having a different beam-shape, for example, to obtain a specific illumination effect.

The luminaires 100, 102 shown in Figs. 4A and 4B may also comprise light emitters 24 which each substantially uniformly illuminate a plurality of scattering elements 26. Such an arrangement may be beneficial as the light emitters 24 typically are relatively expensive. However, a distance between the light emitter 24 and the plurality of scattering elements 26 it illuminates may be relatively large to ensure uniform illumination of the scattering elements 26 by the light emitter. Such increase in distance would increase a height of the luminaires 100, 102.

The luminaires 100, 102 shown in Figs. 4A and 4B may also be used as backlighting system 100, 102 in backlit video screens, advertising boards and poster boxes (not shown).

It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims.

In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention may be implemented by means of hardware comprising several distinct elements. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.