WO2008152576A1

WO2008152576A1 - Lighting device

Info

Publication number: WO2008152576A1
Application number: PCT/IB2008/052281
Authority: WO
Inventors: Elvira J. M. Paulussen
Original assignee: Koninklijke Philips Electronics NV
Current assignee: Koninklijke Philips NV
Priority date: 2007-06-14
Filing date: 2008-06-10
Publication date: 2008-12-18
Anticipated expiration: 2009-12-14
Also published as: TW200914872A

Abstract

A lighting device comprising a plurality of optical devices (10) arranged in a planar distribution and a first lens plate (30) is presented. Each optical device (10) comprises at least one radiation source (11) and an optical element (12) being arranged to create a substantially collimated radiation beam (20) from radiation generated by the at least one radiation source (11), and the first lens plate (30) extends along the plurality of optical devices (10) and comprises a plurality of first sub-lenses(31), in which each first sub-lens (31) projects a part of the radiation beam (20) at an illumination window (50), such that the projections of each first sub-lens (31) at least partially overlap. Also, a method for providing such lighting device is presented.

Description

Lighting device

TECHNICAL FIELD

The present invention relates to a lighting device and a product having such lighting device, said lighting device comprising a plurality of optical devices arranged in a planar distribution and a first lens plate. The present invention also relates to a method for providing such lighting device.

BACKGROUND ART

Light-emitting diodes (LEDs) are well known in the prior art. A LED is formed by a semiconductor die, with a P-type semiconductor layer and an N-type semiconductor layer positioned on top of each other. A PN junction is defined between the P- type semiconductor layer and the N-type semiconductor layer. When a voltage is applied to the LED, holes in the P-type semiconductor layer and electrons in the N-type semiconductor layer are attracted and meet at the PN junction. When holes and electrons combine, photons are created, resulting in a radiation beam (light). The LED may sit in a reflective cup that acts as a heat sink for transporting heat generated by the LED and a reflector for reflecting the created radiation beam.

LEDs typically emit a single wavelength of light, depending on the band-gap energy of the materials forming the PN junction. Nowadays, a variety of colors can be generated on the basis of the material used for making the LED. For instance, LEDs made with gallium arsenide produce infrared and red light. Other examples are gallium aluminum phosphide (GaAlP) for green light, gallium phosphide (GaP) for red, yellow and green light and zinc selenide (ZnSe) for blue light.

LEDs typically produce non-collimated radiation beams. Therefore, efforts have been made to collimate the light generated by a LED. Especially in the field of high- power LEDs, mixing of colors as well as beam-shaping and collimation optics are topics of frequent discussion. This is an effect of LEDs becoming more and more important in lighting applications. Mixing techniques using red, green and blue LEDs for obtaining white light include for example mixing rods, light guides or reflectors, or a combination of these. A disadvantage of these solutions is that they can be large and bulky in order to obtain good color mixing and good beam shaping. Modular high flux spot light sources making use of these techniques are almost impossible for compact lighting devices, scaling their sizes to huge dimensions.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improvement of the above techniques and prior art. More particularly, it is an object of the present invention to provide a lighting device, such as a modular spot light source, which has a high degree of compactness and color homogeneity. The above objective is provided according to a first aspect of the invention by a lighting device comprising a plurality of optical devices arranged in a planar distribution and a first lens plate, wherein each optical device comprises at least one radiation source and an optical element being arranged to create a substantially collimated radiation beam from radiation generated by the at least one radiation source. Further, the first lens plate extends along the plurality of optical devices and comprises a plurality of first sub-lenses, in which each first sub-lens projects a part of the radiation beam at an illumination window, such that the projections of each first sub-lens at least partially overlap. The lighting device is advantageous in that it provides a compact light source having a high amount of light flux. The lighting device may further comprise a second lens plate extending along the plurality of optical devices and having a plurality of second sub-lenses, wherein the second sub-lens of the second lens plate images a corresponding first sub-lens of the first lens plate at the illumination window, such that the images of each first sub-lens of the first lens plate projected by the second sub-lens of the second lens plate at least partially overlap. Thus, the shape of the illumination window can be controlled by choosing the aperture shape of the first sub-lenses of the first lens plate.

The plurality of optical devices may be stacked in a two dimensional array, which is suitable for lighting applications and provides a high level of modularity.

Each radiation source may be a light emitting diode, which is advantageous in that cheap and efficient components are used. The optical element of each optical device may comprise a transparent body including a first surface, a second surface and a cavity formed within at least the second surface, the cavity having a third surface, the second surface comprising a reflective region extending radially away from the cavity, and the first surface comprising an annular zone configured to provide internal reflection folding and an optical refractive transition between the transparent body and the exterior of the transparent body.

The optical element of each optical device may also comprise a compound parabolic concentrator, or it may comprise an outer reflective portion and an inner refractive portion. Any of these embodiments is advantageous in that common components known per se are used.

Each optical device may comprise a plurality of colored light emitting diodes, which is advantageous in that the lighting device may emit any color.

Each optical device may comprise only one radiation source, whereby a simple arrangement is provided.

The above objective is provided according to a second aspect of the invention by a method for providing a lighting device. The method comprises the steps of arranging a plurality of optical devices in a planar distribution, creating a substantially collimated radiation beam from radiation generated by at least one radiation sources of each optical device, arranging a first lens plate extending along the plurality of optical devices and comprising a plurality of first sub-lenses, and projecting, by means of each first sub-lens, a part of the radiation beam at an illumination window, such that the projections of each first sub-lens at least partially overlap. The advantages of the first aspect of the invention are also applicable for this second aspect of the invention. The method may further comprise the steps of arranging a second lens plate extending along the plurality of optical devices and comprising a plurality of second sub- lenses, and imaging, by means of each second sub-lens, a corresponding first sub-lens at an illumination window, such that the images of each first sub-lens of the first lens plate projected by the second sub-lens of the second lens plate at least partially overlap. The method may further comprise the step of stacking the plurality of optical devices in a two dimensional array.

According to a third aspect of the invention, a product is provided comprising a holder and a lighting device according to the first aspect of the invention. The advantages of the first aspect of the invention are also applicable for this third aspect of the invention. Other objectives, features and advantages of the present invention will appear from the following detailed disclosure, from the attached dependent claims as well as from the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying schematic drawings, in which

Fig. 1 shows schematically a first optical element according to prior art. Fig. 2 shows schematically a second optical element according to prior art.

Fig. 3 shows schematically a third optical element according to prior art. Fig. 4 shows schematically a fourth optical element according to prior art. Fig. 5 is a side view of an optical device.

Fig. 6 is a side view of an optical device and a first lens plate and a second lens plate.

Fig. 7 is a side view of an optical device and a first lens plate. Fig. 8 is a side view of a lighting device according to one embodiment of the present invention.

Fig. 9 is a side view of a lighting device according to a second embodiment of the present invention.

Fig. 10 is a perspective view of a lighting device according to another embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS A lighting device 100 comprises a plurality of optical devices 10 and a first lens plate 30. Each optical device 10 has at least one light source 11 and an optical element

12 for collimating the light emitted from the light source 11.

In Figs. 1 - 4, different optical elements are shown. Fig. 1 shows an optical device 10 of a type disclosed in US 2004/0246606 Al. Fig. 1 is a cross-sectional side view of such an optical element 12, which is rotationally symmetric. The optical element 12 is formed by an entrance surface 13 and an exit surface 14. In fact, a light emitting diode (LED)

11 is positioned in a cavity 15 formed in the entrance surface 13. The LED 11 comprises a P- layer and an N-layer, as described above, and is positioned in a dome-shaped cover 16. Fig. 1 also shows electric cables 17, which are connected to the LED 11 for its electric energy supply.

Radiation generated by the LED 11 enters the optical element 12 via entrance surface 13. Subsequently, the radiation beam is reflected by the exit surface 14 by means of TIR (Total Internal Reflection) and the entrance surface 13 before it exits the optical element

12 via the exit surface 14. Exit surface 14 may be partly a mirror, for instance, in the centre near LED 11. Entrance surface 13 is preferably a mirror. The shape of the entrance surface 13 and the exit surface 14 is chosen to be such that the radiation beam exits the optical element 11 in a substantially collimated form.

Fig. 2 schematically depicts an alternative embodiment, showing an alternative optical element 12' according to the prior art. The LED 11 is positioned completely inside this alternative optical element 12'. Again, the radiation generated by the LED 11 is reflected twice inside the optical element 12', first by exit surface 14', and subsequently by a rear surface 13', before the radiation exits the optical element 12' via exit surface 14'. The optical element 12' is also rotationally symmetric. In Fig. 3, a third embodiment of an optical element 12" is depicted. The optical element 12" is a compound parabolic concentrator having an entry surface 13" and an exit surface 14". A LED (not shown) is optically coupled to the light entry surface 13" and light propagates under reflection through the optical element 12". Collimated light is extracted from the light exit surface 14". The optical element 12" can either be hollow or solid. In case of a hollow optical element 12", the reflection occurs due to a coated surface of the optical element 12". In case of a solid optical element 12", the reflection occurs due to a coated surface of the optical element 12" and/or due to TIR.

Fig. 4 depicts a fourth embodiment of an optical element 12"' for collimating light emitted from a light source (not shown). The collimator 12"' has an entry surface 13"' and an exit surface 14"'. The collimator 12'" has an outer reflective portion 18 and an inner refractive portion 19. The inner refractive portion 19 can be a lens or a lens pair. A part of the light incident on the light entry surface 13"' is reflected based on TIR (total internal reflection) on the outside part of the collimator 18, and another part of the light is refracted by the inner lens(es) 19. A collimated light beam is extracted from the light exit surface 14"'. In one embodiment, the optical device 10 has several light sources 11, 11' etc.

Each light source 11 may be a single LED or a plurality of LEDs, such that each light source 11, 11 ' is a group of LEDs. In Fig. 5, the optical device 10 has two light sources 11 and 11 '. The light source 11 emits red color, and 11 ' emits amber light. In another embodiment, the optical device 10 may have another number of light sources, e.g. four, wherein each light source emits light from any color. Of course, any suitable number of LEDs having any combination of colors may be used, as will be evident to a skilled person.

As can be seen in Fig. 5, the optical element 10 produces a substantially collimated radiation beam. As already stated above, the term "collimated" is used herein to denote a radiation beam that is substantially parallel, for example 0-10°. For reasons of simplicity, the radiation beam 20 is depicted in the Figure as a 'perfect' collimated radiation beam.

It will be understood that radiation beam 20 does not have a homogeneous color, but will be predominantly red at the top and predominantly amber at the lower side. However, it will be evident to a skilled person that the radiation beam 20 as emitted by the optical device 10 is already mixed to a certain extent if the radiation source, i.e. the composition of the two LEDs 11, 11 ', is relatively small with respect to the optical element 10.

A device is provided for mixing the radiation emitted by the different LEDs 11, 11 '. In order to achieve this, a first lens plate 30 and a second lens plate 40 are provided in accordance with an embodiment, as is schematically depicted in Fig. 6. The first lens plate 30 comprises a plurality of sub-lenses 31 and the second lens plate 40 comprises a plurality of sub-lenses 41. The sub-lenses 31, 41 of the lens plates 30, 40 are also referred to as lens lets. It will be understood that many alternative lens plates 30, 40 are conceivable, e.g. rectangular shaped and having rectangular shaped sub-lenses, or rectangular shaped and having circular shaped sub-lenses, or circular shaped and having hexagonal sub-lenses. The aperture shape of the lens lets 31 can be different from the aperture shape of the lens lets 41. E.g. the lens lets 31 can be rectangular and the lens lets 41 can be round, or vice versa. Based on Fig. 6, it can be seen that a lens plate 30 is positioned behind the optical device 10, comprising a number of sub-lenses 31. Each sub-lens 31 has substantially the same focal distance, approximately f 1. The second lens plate 40 is positioned substantially at a distance fl from the first lens plate 30, and sub-lenses 41 of the second lens plate 40 has substantially the same focal distance f2, which preferably is of the same magnitude as fl .

It can be seen in Fig. 6 that the second lens plate 40 images the lens lets 31 of the first lens plate 30 onto an illumination window 50. This aspect is indicated by the broken lines in Fig. 5. Note that the illumination window 50 is relatively far remote from the second lens plate 40 and, for practical purposes, may thus be considered to be the far field. The first lens plate 30 may be in the focal plane of the second lens plate 40, but may also be near the focal plane of the second lens plate 40.

The second lens plate 40 can have a plurality of second sub-lenses 41, arranged such that they image a corresponding first sub-lens 31 of the first lens plate 30 at the illumination window 50, such that the images of each first sub-lens 31 of the first lens plate 30 projected by the second sub-lens 41 of the second lens plate 40 at least partially overlap.

This illumination window 50 may be in the far field and may coincide with an object that is to be illuminated. In practice, such an object may have a surface that is to be illuminated by the light sources 11, 11 ', such as, for instance, a painting, a table, a window, a building, etc. The techniques described here may also be used in projection display applications. For projection display applications, two lenses are preferably added in order to bring the illumination window to the near field. It is to be noted that illumination window 50 is relatively far remote from the second lens plate 40, which is only schematically depicted in the Figures.

The term "far field" is used herein to denote that the illumination window is relatively far remote from the second lens plate 40. In practice, the lens plate 40 may have a diameter of only a few centimeters, in which case the term far field could refer to a distance of approximately 2 m. Two sub-parts of the radiation beam 20 are depicted in Fig. 6: a red sub-part and an amber sub-part. The red sub-part is projected in the far field via a sub-lens 31 of the first lens plate 30 and a corresponding sub-lens 41 of the second lens plate 40. The amber sub-part is projected in the far field via a further sub-lens 31 of the first lens plate 30 and a further corresponding sub-lens 41 of the second lens plate 40. Fig. 6 shows that the red sub-part and the amber sub-part are mixed to a large extent in the illumination window 50. In fact, the radiation emitted by all of the light sources 11, 11 ' is substantially mixed in the illumination window 50. If the light sources 11, 11 ' emit different colors, these colors are mixed in the illumination window, creating, for instance, white light. It will be understood that the number of sub-lenses 41 of the second lens plate

40 may be equal to the number of sub-lenses 31 of the first lens plate 30, as each sub-lens 41 of the second lens plate 40 images the contour of a corresponding sub-lens 31 of the first lens plate 30. In order to do this, the focal distance f2 of the sub-lenses 41 of the second lens plate 40 may be substantially equal to the focal distance fl of the sub-lenses 31 of the first lens plate 30. The first sub-lenses 31 of the first lens plate 30 may also be positioned at a distance from the corresponding sub-lenses 41 of the second lens plate, which distance is equal to the focal distance of the second sub-lenses 41 of the second lens plate 40.

It will also be understood that the illumination window is in the far field, although the figures show it relatively close to the second lens plate 40. It will further be understood that the focal distances of the sub-lenses 31, 41 and the mutual distance between the first lens plate 30 and the second lens plate 40 do not necessarily need to be exactly equal to each other. Variations are allowed, for instance, variations that are equal to the thickness of the lens plates 30, 40. The focal distances of the sub-lenses 31, 41 and the distance between the first lens plate 30 and the second lens plate 40 may be adjusted on the basis of the characteristics of the radiation beam 20 or on the basis of the desired size of the illumination window 50 at a certain distance.

Based on the above, it will be understood that the shape of each sub- projection, and thus the illumination window 50, is determined by the shape of the sub-lens 31 of the first lens plate 30.

In one embodiment, the second lens plate 40 is omitted, as is shown in Fig. 7. As will be evident to a skilled person, the second lens plate 40 no longer has an imaging function (broken lines in Fig. 6). Mixing of the radiation from different radiation sources (light sources 11, 11 ') and beam-shaping in accordance with the set-up of Fig. 6 therefore has a higher quality as compared with beam- shaping, i.e. collimation, of the set-up as shown in Fig. 7.

A first embodiment of a lighting device 100 is shown in Fig. 8. Fig. 8 shows a cross-sectional view of a plurality of optical devices 10 stacked in an array. Each optical device has several light sources 11, 11 ', and each light source is at least one LED. In one embodiment, the optical device 10 has only one colored LED. In another embodiment, the optical device 10 has multiple colored LEDs. In the embodiment shown in Fig. 8, the optical elements 12 are of the kind depicted in Fig. 2. However, in other embodiments of the present invention the optical elements can be of any type described herein, e.g. as shown in Fig. 1, Fig. 3 or Fig. 4, or any collimating components known per se. Further, the lighting device 100 comprises a first lens plate 30 extending over the array of optical devices 10. Fig. 8 also shows a second lens plate 40, extending over the array of optical devices 10.

In Fig. 9, the optical elements of the lighting device 90 are compound parabolic concentrators 92. The lateral compactness of the lighting device is thereby improved. In one embodiment each compound parabolic concentrator 92 is approximately 1 cm in diameter. A collimator as shown in Fig. 1 may be up to 5 cm. Thus, a lighting device as shown in Fig. 9 has 25 times more optical elements than the lighting device as shown in Fig. 8. Further, the first lens plate and the second lens plate are incorporated in one single component 94. Light losses are thereby reduced, and the lighting device 90 can be even more compact. Fig. 10 shows a perspective view of a lighting device 100 according to one embodiment of the present invention. The optical devices 10 are arranged in a planar distribution in the shape of a two-dimensional array. The first lens plate 30, comprising a number of lens lets (not shown) is arranged behind the optical devices 10. Further, the second lens plate 40 is arranged behind the first lens plate 30.

In other embodiments, the first lens plate 30 may have a size which is different from that of the second lens plate 40. The second lens plate 40 can be relatively small in comparison with the first lens plate 30. The optical device 10, the first lens plate 30 and the second lens plate 40 may accommodated in a holder 60, providing a small and compact product.

The sub-lenses 31 of the first lens plate 30 can be positioned in a semi-circular configuration or the like. Each sub-lens 31 of the first lens plate 30 may have a different orientation. Accordingly, the sub-lenses 41 of the second lens plate 40 are positioned in a semi-circular configuration, but in an opposite direction. Each sub-lens 41 of the second lens plate 40 may have a different orientation. Consequently, the first lens plate 30 may have a convex (rounded) shape as viewed in the direction of propagation of the radiation beam 20, whereas the second lens plate 40 may have a concave (hollow) shape as viewed in the direction of propagation of the radiation beam 20.

It will be evident to a skilled person that a first sub-lens 31 of the first lens plate 30 and a second sub-lens 41 of the second lens plate 40 may have a similar tilt with respect to their orientation as shown in Fig. 6, but in opposite directions. The orientation of each second sub-lens 41 of the second lens plate 40 may be chosen to be dependent on the orientation of the first sub-lens 31 of the first lens plate 30, or vice versa.

In accordance with a further embodiment, all sub-lenses 31 of the first lens plate 30 are positioned in a straight line with tilted orientations, and the sub-lenses 41 of the second lens plate 40 are also positioned in a straight line with tilted orientations. Each first sub-lens 31 of the first lens plate 30 may have an opposite tilt with respect to the tilt of the second sub-lens 41 of the second lens plate 40. Further, the optical devices 10 may be arranged in a concave structure, and the first lens plate 30 and the second lens plate 40 is correspondingly arranged in a concave arrangement.

The focal distances of the first and second sub-lenses 31, 41 of the first and second lens plates 30, 40 may vary as the distances between the corresponding sub-lenses 31, 41 from the first and second lens plates 30, 40 also vary. The invention has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims.

Claims

CLAIMS:

1. A lighting device comprising a plurality of optical devices (10) arranged in a planar distribution and a first lens plate (30), wherein each optical device (10) comprises at least one radiation source (11) and an optical element (12) being arranged to create a substantially collimated radiation beam (20) from radiation generated by the at least one radiation source (11), and the first lens plate (30) extends along the plurality of optical devices (10) and comprises a plurality of first sub-lenses(31), in which each first sub-lens (31) projects a part of the radiation beam (20) at an illumination window (50), such that the projections of each first sub-lens (31) at least partially overlap.

2. A lighting device according to claim 1, further comprising a second lens plate (40) extending along the plurality of optical devices (10) and having a plurality of second sub-lenses (41), wherein the second sub-lens (41) of the second lens plate (40) images a corresponding first sub-lens (31) of the first lens plate (30) at the illumination window (50), such that the images of each first sub-lens (31) of the first lens plate (30) projected by the second sub-lens (41) of the second lens plate (40) at least partially overlap.

3. A lighting device according to any one of claims 1 or 2, wherein the plurality of optical devices (10) are stacked in a two dimensional array.

4. A lighting device according to any one of claims 1 - 3, wherein each radiation source (11) is a light emitting diode.

5. A lighting device according to any one of claims 1 - 4, wherein the optical element (12) of each optical device (10) comprises a transparent body including a first surface (14), a second surface (13) and a cavity (15) formed within at least the second surface (13), the cavity (15) having a third surface (13), the second surface (13) comprising a reflective region extending radially away from the cavity (15), and the first surface (13) comprising an annular zone configured to provide internal reflection folding and an optical refractive transition between the transparent body and the exterior of the transparent body.

6. A lighting device according to any one of claims 1 - 4, wherein the optical element (12) of each optical device (10) comprises a compound parabolic concentrator.

7. A lighting device according to any one of claims 1 - 4, wherein the optical element (12) of each optical device (10) comprises an outer reflective portion (18) and an inner refractive portion (19).

8. A lighting device according to any one of claims 1 - 7, wherein each optical device (10) comprises a plurality of colored light emitting diodes.

9. A lighting device according to any one of claims 1 - 7, wherein each optical device (10) comprises only one radiation source (11).

10. A method for providing a lighting device, said method comprising the steps of arranging a plurality of optical devices in a planar distribution, creating a substantially collimated radiation beam from radiation generated by at least one radiation sources of each optical device, arranging a first lens plate extending along the plurality of optical devices and comprising a plurality of first sub-lenses, and projecting, by means of each first sub-lens, a part of the radiation beam at an illumination window, such that the projections of each first sub-lens at least partially overlap.

11. A method according to claim 10, wherein the method further comprises the steps of arranging a second lens plate extending along the plurality of optical devices and comprising a plurality of second sub-lenses, and imaging, by means of each second sub-lens, a corresponding first sub-lens at an illumination window, such that the images of each first sub-lens of the first lens plate projected by the second sub-lens of the second lens plate at least partially overlap.

12. A method according to any one of claims 10 or 11, wherein the method further comprises the step of stacking the plurality of optical devices in a two dimensional array.

13. A product comprising a holder and a lighting device according to any one of claims 1 - 9.