WO2011027267A1

WO2011027267A1 - Illumination system and luminaire

Info

Publication number: WO2011027267A1
Application number: PCT/IB2010/053838
Authority: WO
Inventors: Erik Boonekamp; Antonius Petrus Marinus Dingemans; Martijn Henri Richard Lankhorst; Michel Cornelis Josephus Marie Vissenberg
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2009-09-01
Filing date: 2010-08-26
Publication date: 2011-03-10

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 light source comprises a light-emitting surface (21) having a dimension substantially equal to a narrow end (50) of the tapered reflector. The tapered reflector comprises an edge wall (60) connecting the narrow end (50) and the wide end (40). The edge wall is configured for diffusely reflecting light from the light source towards the wide end. A height (h) of the tapered reflector is selected to be equal to or larger than a minimum height (hmin), which defines a lowest height value in a range of height values. In the range of height values, a glare value of the illumination system remains substantially constant. The 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.

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, shop lights or, for example, shop window lights.

Typically, luminaires for illuminating public places and, for example, for use in offices have to comply with glare regulations. Glare results from excessive contrast between bright and dark areas in the field of view. Glare can, for example, result from exposure to view of the filament of an unshielded or poorly shielded light source. Especially when using LEDs, a 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, European EN 12464-1 standard, which dictates that the emission of light should not exceed a luminance of 1000 cd/m² 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 enables the creation of a beam having 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 provided by 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 a 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 a first aspect of the invention the object is achieved with an illumination system as claimed in claim 1. According to a second aspect of the invention, the object is achieved with a luminaire as claimed in claim 9. 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 arranged at a narrow end of the tapered reflector and having a dimension substantially equal to a dimension of the narrow end of the tapered reflector, and being used for emitting substantially diffuse light towards a wide end of the tapered reflector. The tapered reflector comprises an edge wall connecting the narrow end and the wide end, the edge wall diffusely reflecting light from the light source towards the wide end. The height of the tapered reflector is a dimension measured substantially parallel to a symmetry axis of the tapered reflector. The height of the tapered reflector is selected to be equal to or larger than a minimum height, which is a smallest height value in a range of height values of the tapered reflector. In the range of height values the glare value of the illumination system remains substantially constant.

The symmetry axis of the tapered reflector is typically arranged from the center of the narrow end to the 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 have a truncated cone-shape or a truncated pyramid-shape or any other shape. The intersection between the edge of the wide end and/or narrow end and the imaginary surface may be circular, elliptical or 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 edge wall comprises diffusely reflecting material which typically is a white, diffusely reflecting material, typically having a reflectivity of 95% to 98%. The tapered reflector according to the invention may also be indicated as a concave reflector, and may be embodied with or without a neck at its narrow end; the narrow end may be open or closed, in which latter case 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 of 65 degrees.

An effect of the illumination system according to the invention 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 diffusely reflecting edge wall of the tapered reflector. This typical combination generates this specific behavior, being that 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 the height increases. At a height of the tapered reflector below the minimum height, the glare value as measured from the illumination system decreases 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. However, increasing the height of the tapered reflector typically alters the shape of a light beam emitted by the illumination system. For this reason, 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 glare in known illumination systems only are capable of generating a single beam shape at a single glare value. By adapting the known prismatic optical plate, the beam shape may be adapted, but typically also results in an increase of the glare value of the system. Therefore, 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 maintaining the glare value of the illumination system substantially 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 a substantially constant, low glare value. A further effect of using the illumination system according to the invention is that the minimum height within the range of height values having substantially constant glare often substantially coincides with a glare value minimum of the illumination system. The amount of flux which may be introduced 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 values is found at or near a glare value minimum of the illumination system, the maximum light flux may be introduced into the illumination system according to the invention while the glare value within the range of height values remains within the defined normalized emission profile. Therefore, 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 the possibility 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 application 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 using, for example, injection-molding or plastics-deformation processes. After applying a layer to the edge wall, thus generating a diffusely reflecting edge wall, the tapered reflector may be arranged around the light source for generating the illumination system having a limited glare value at relatively low cost.

A shape of the light beam as emitted by the illumination system depends on, amongst others, the shape of the tapered reflector. A shape of the tapered reflector which generates a specific predefined beam shape may be determined using, 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 is such that 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 the range of height values is such that 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 be generated from the illumination system without exceeding the glare-norm excessively. In experiments, the inventors have established that a variation of the glare value of 10% is still acceptable when, for example, the illumination system is used 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 introduced in the illumination system may be better optimized and may be closer to the maximum light flux which may be introduced without exceeding the glare norm of 1000 cd/m² at an angle of 65 degrees.

In an embodiment of the illumination system, the light source comprises an organic light emitting diode emitting light across a surface substantially equal to the light emitting surface. A benefit of using the organic light emitting diode as a light source is that this organic light emitting diode typically already emits substantially diffuse light uniformly across the light-emitting surface of the organic light emitting diode. Therefore, no additional measures are required to provide uniform illumination of the narrow end of the reflector. Furthermore, as 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 comprising the scattering element, the scattering 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 an embodiment of the illumination system comprising the scattering element, the scattering element comprises holographic scattering structures for diffusely scattering the light from the light emitter. The 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.

In an embodiment of the illumination system comprising the scattering element, the scattering element comprises luminescent material embedded in the scattering element for converting light emitted by the light emitter 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 emitter into light of a different color. When, for example, the light emitter emits ultraviolet light, the scattering 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 provides a mixture of light of a predefined perceived color. Alternatively, the light emitter emits visible light, for example, blue light, and part of the blue light is converted by luminescent material into light of a longer 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 comprising the scattering element, the scattering element comprises luminescent material applied to a surface of the scattering 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 scattering element facing the light emitter, the layer of luminescent material is not immediately visible from the outside of the illumination system. In the example in which the light emitter emits blue light, a part of which is converted by the luminescent material into yellow light, the color of 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. Therefore, when applying the luminescent material at the surface of the scattering element facing towards the light emitter, the luminescent material is not directly visible from the outside, thus reducing the yellow appearance of the scattering element and hence the confusion to users of the illumination system.

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 convex-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, thereby further reducing glare.

A further benefit of the convex-shaped light emitting surface is that it provides space 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 mount both the tapered reflector and the convex-shaped light emitting surface, thus enhancing the ease of manufacturing the illumination system. In addition, the convex-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 introducing a higher light flux in the illumination system having inwardly curved edge walls, compared to illumination systems having substantially straight edge walls, while still observing the glare norm. The exact curvature required of the edge wall may depend on the shape and size of the light emitting surface of the light source and may be determined using, for example, 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, be used to manually or automatically adapt the curvature of the edge wall to adapt the beam shape of the light emitted by the illumination system. Thus, 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. As the glare value is substantially constant for different heights of the tapered reflector, the adaptation of the height may be used to alter the 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. Adaptation of the height of the tapered reflector, for example, manually or via motor-control, causes the deformable material to deform, thereby adapting the shape of the edge wall so as to alter the beam shape as emitted by the illumination system. Thus, an adaptable illumination system in which the beam shape may be adapted is obtained.

According to a second aspect of the invention, the object is achieved by means of 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 at least a second illumination system having a second beam shape, different from the first beam shape. With both the first illumination system and the second illumination system accommodated in the luminaire, a user can 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 overall illumination of the room is required. A combination of both beam shapes may allow general illumination of the room together with a well-illuminated desk - typically required for 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 systems, having a different beam shape to obtain, for example, 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, such as an elliptical cross section or, for example, a polygonal cross section. The plurality of illumination systems in the luminaire may be arranged in a close-packed two-dimensional array of illumination systems 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. A regular-packed arrangement of the plurality of illumination systems may thus be obtained, while the different curvatures of the edge walls allow further different beam shapes 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 independently of the second illumination system. This controller may simply consist of a pair of switches by means of which the set of first illumination systems in the luminaire may be switched independently of the set of second illumination systems, allowing a user to either only switch on the set of first illumination systems, the set of second illumination systems, or both the set of first illumination systems and the set of second illumination systems. Alternatively, the controller may comprise dimmers for dimming the set of first illumination systems independently of the set of second illumination systems. Also beam-shape adaptation means may be present to adapt a beam shape of the first illumination system of the set of first illumination systems independently of the beam shape of the second illumination system of 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 controlling of the curvature of the first edge wall and/or of the second edge wall may be a continuous control process, 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 by means of 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. 1 A 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 at varying heights 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. 4 A and 4B show different embodiments of a luminaire according to the invention.

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

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 having a dimension substantially identical to a dimension of a narrow end 50 of the tapered reflector 30, and 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 is covered with a white, diffusely reflecting material, for example, having a reflectivity of 95% to 98%. 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 has been 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 the diffusely reflecting edge wall 60 of the tapered reflector 30. This typical combination generates this specific behavior, being that 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 the height h increases. 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%). 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 a relatively low glare value. However, such a small light source typically is too bright to look into and would provide visual discomfort to a user.

As can be seen from Fig. IB, at a height h of the tapered reflector 10 below the minimum height hmin, the glare value as measured from the illumination system 10 shown in Fig. 1 A decreases 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 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, the shape of a light beam emitted by the illumination system 10 does change (see also Figs. 2A to 2C). Thus, using the illumination system 10 as shown in Fig. 1 A, 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 the graph of Fig. IB. Choosing, for example, a different shape of the edge wall 62 (see Figs. 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). Since 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 shown in Fig. IB.

As can be seen from Fig. IB, the glare value within the range of height values having a substantially constant glare value substantially coincides with a glare value minimum of the illumination system 10. This allows light designers to introduce a maximum light flux at which the resulting glare is at or just below the maximum acceptable glare value as defined in the European EN 12464-1 standard. Therefore, the illumination system 10 as shown in Fig. 1A may be designed to provide a maximum flux of light while the glare value of the illumination system 10 remains below the predefined glare level, thus offering designers the possibility 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 using, for example, injection-molding or plastics- deformation processes. After applying a layer to the edge wall, thus 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 a 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 emit substantially diffuse light uniformly across the light emitting surface 21 of the organic light emitting diode 22. Thus, no additional measures are required to provide uniform illumination of the narrow end 50 of the tapered reflector 30. Furthermore, as organic light emitting diodes 22 typically are relatively thin, the overall height of the illumination system 10 may be smaller than that of 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 light designers with a high degree of flexibility in designing and controlling illumination systems 10, 12, 14, 16.

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 frequently preferred beam shape has a substantially block-shaped emission distribution the center of which 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 depend on the shape and size of the light emitting surface 21 of the light source 20 and may be determined using, for example, optical modeling software, also known as ray-tracing programs, such as ASAP^®, lighttools^®, etc.

The illumination system 12 as shown in Fig. 2 A may comprise curvature means (not shown) for adapting a curvature of the edge wall 62 and hence the emission distribution of the illumination system 12. The edge wall 62 may, for example, be

manufactured of deformable material. Therefore, 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 in order to adapt the curvature of the edge wall 62 to adapt the emission distribution of the light emitted by the illumination system 12. Since 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. 2 A 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 concave-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. 1 A, 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 a relatively high efficiency of the emission of diffuse light from the light source 20.

The scattering element 26 may additionally or alternatively comprise 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 provides a mixture of light of 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 longer 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, part of which is converted by the luminescent material into yellow light which, in combination, provides the perceived white light emitted. 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 facing the light emitter 24, the luminescent material is not directly visible from the outside, reducing the yellow appearance of the scattering element 26 and thus 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 Y₃Al₅0i₂:Ce³⁺ (further also referred to as YAG:Ce) which converts part of the impinging blue 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 light, determining the color of the light emitted by the illumination system 10, 12, 14, 16. The amount of blue light which is converted by the luminescent material may, for example, be determined by the layer thickness of the luminescent material, or, for example, by the concentration of the YAG:Ce particles distributed in the scattering element 26. Alternatively, for example, CaS:Eu²⁺ (further also referred to as CaS:Eu) may be used, which converts part of the impinging blue 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, which ultraviolet light may be converted by the luminescent material into substantially white light. For example a mixture of BaMgAlioOi7:Eu²⁺ (converting ultraviolet light into blue light), CagMg(Si0₄)₄Cl₂: Eu²⁺,Mn²⁺ (converting ultraviolet light into green light), and Y₂0₃:

Eu³⁺,Bi³⁺ (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, which relates to the calculated glare value versus the height for the illumination system of Fig. 2A. Fig. 2B shows a similar behavior to that 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 the comparison between the graphs of Fig. IB and Fig. 2B, 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 this difference that the edge wall 62 is curved inward compared 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 of 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 introducing 20 to 30% more light flux in the second illumination system 14 before the same glare value is attained 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 using, 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 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 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 16 A. 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. Since both the first illumination system 16A and the second illumination system 16B are comprised in the luminaire 100, a user can choose either light emitted by the first illumination system 16A or 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 light is required at the surface below the luminaire, for example, a desk or table, while the second beam shape may be used when overall illumination of the room is required. A combination of both beam shapes may allow general illumination of the room together with a well-illuminated desk - typically required for 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 systems 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 Fig. 2A 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 systems 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. With both the first illumination system 12A and the second illumination system 12B accommodated in the luminaire 100, a user can choose either of light emitted by the first illumination system 12 A, light emitted by 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 elements 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 connected to 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, using 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. As the assembly is made relatively quickly and easily, allowing comparatively known and inexpensive production processes to be used, for example, for the array 124 of tapered reflector cavities 32, such a luminaire 102 can be produced relatively cost-effectively.

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, the distance between the light emitter 24 and the plurality of scattering elements 26 illuminated by the light emitter may be relatively large to ensure uniform illumination of the scattering elements 26 by the light emitter. Such an increase in distance would increase the 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.

Claims

CLAIMS:

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

the light source (20) comprising a light-emitting surface (21) being arranged at a narrow end (50) of the tapered reflector (30, 32) and having a dimension substantially equal to a dimension of the narrow end (50) of the tapered reflector (30, 32), and being used for emitting substantially diffuse light towards a wide end (40) of the tapered reflector (30, 32), and

the tapered reflector (30, 32) comprising an edge wall (60, 62) connecting the narrow end (50) and the wide end (40), the edge wall (60, 62) diffusely reflecting light from the light source (20) towards the wide end (40), a height (h) of the tapered reflector (30, 32) being a dimension measured substantially parallel to a symmetry axis (A) of the tapered reflector (30, 32),

the height (h) of the tapered reflector (30, 32) being selected to be equal to or larger than a minimum height (hmin) being a lowest height value in a range of height values of the tapered reflector (30, 32), and in the range of height values the glare value of the illumination system (10, 12, 14, 16) remaining substantially constant.

2. Illumination system (10, 12, 14, 16) as claimed in claim 1, wherein the range of height values is such that a variation of the glare value within the range of height values of the tapered reflector (30, 32) is less than 10% of an average glare value (Ga) within the range of height values, and/or wherein the range of height values is such that the variation of the glare value within the range of height values of the tapered reflector (30, 32) is less than 5% of the average glare value (Ga) within the range of height values.

3. Illumination system (10, 12, 14, 16) as claimed in claim 1 or 2, wherein the light source (20) comprises:

an organic light emitting diode (22) emitting light across a surface substantially equal to the light emitting surface (21), or

a light emitter (24) and a scattering element (26) comprising the light emitting surface (21), the light emitter (24) being configured for substantially evenly illuminating the scattering element (26).

4. Illumination system (10, 12, 14, 16) as claimed in claim 3, comprising the scattering element (26), wherein the scattering element (26) comprises:

diffuser means (26) for diffusely scattering the light from the light emitter

(24), and/or

holographic scattering structures for diffusely scattering the light from the light emitter (24), and/or

luminescent material embedded in the scattering element (26) for converting light emitted by the light emitter (24) into light of a longer wavelength, and/or

luminescent material applied to a surface of the scattering element (26) for converting light emitted by the light emitter (24) into light of a longer wavelength.

5. Illumination system (10, 12, 14, 16) as claimed in any one of the preceding claims, wherein the light-emitting surface (21) of the light source (20) is convexly shaped towards the wide end (40) of the tapered reflector (30, 32).

6. Illumination system (10, 12, 14, 16) as claimed in any one of the preceding claims, wherein the edge wall (62) is curved inward towards the symmetry axis (A) of the tapered reflector (30, 32) for adapting a beam shape of the light emitted by the illumination system (10, 12, 14, 16).

7. Illumination system (10, 12, 14, 16) as claimed in claim 6, wherein the illumination system (10, 12, 14, 16) comprises curvature means for adapting a curvature of the edge wall (60, 62).

8. Illumination system (10, 12, 14, 16) as claimed in claim 7, wherein the curvature means are configured for adapting the height (h) of the tapered reflector (30, 32) for the purpose of adapting the curvature of the edge wall (60, 62).

9. Luminaire (100, 102) comprising the illumination system (10, 12, 14, 16) as claimed in any one of claims 1 to 8.

10. Luminaire (100, 102) as claimed in claim 9, wherein the luminaire comprises at least a first illumination system (10, 12, 14, 16) having a first beam-shape (80) and at least a second illumination system (10, 12, 14, 16) having a second beam- shape (82), different from the first beam shape (80).

11. Luminaire (100, 102) as claimed in claim 10, 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 from a curvature of the second edge-wall (62).

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

13. Luminaire (100, 102) as claimed in claim 12, 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).

14. Luminaire (100, 102) as claimed in claim 12 or 13, wherein the controller (HO) 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).

15. Backlighting system (100, 102) comprising the illumination system (10, 12, 14, 16) according to any one of the claims 1 to 8, or comprising the luminaire (100, 102) as claimed in any one of the claims 9 to 14.