WO2009047727A1

WO2009047727A1 - Light emitting device package, light output system and light output method

Info

Publication number: WO2009047727A1
Application number: PCT/IB2008/054145
Authority: WO
Inventors: Willem L. Ijzerman; Michel C. J. M. Vissenberg
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2007-10-09
Filing date: 2008-10-09
Publication date: 2009-04-16
Also published as: TW200930948A

Abstract

The present invention relates to a light emitting device package (100) with an integrated collimating reflector (104), wherein a light emitting element (102) is arranged in relation to the collimating reflector for producing collimated light. The present invention also relates to a light output system (10) comprising such a package, as well as to a corresponding light output method.

Description

Light emitting device package, light output system and light output method

FIELD OF THE INVENTION

The present invention relates to a light emitting device package, in particular for use in a light output system comprising an optical system adapted to spread or mix light produced by associated light sources and then out-couple the light from the device to provide illumination. The present invention also relates to a corresponding light output method.

BACKGROUND OF THE INVENTION

An example of light output system comprising such an optical system is disclosed in the document WO2006/034831. Specifically, WO2006/034831 discloses a thin illumination system in which a plurality of light sources, emitting light from different colors, couple their light sideways, i.e. substantially parallel to a plane of light out-coupling, into a light guiding means through recesses distributed over the light guiding means. Providing a specially structured surface pattern, in combination with light in-coupling parallel to the plane of light out-coupling of the light guiding means, allegedly allows to obtain a good color mixing of the differently colored light originating from the plurality of light sources. The light then is only coupled out after it has been in the light guiding means for a significant long time such that the light emanating from different light sources is significantly mixed. Namely, when a light ray hits the structured surface pattern, the vertical component of its propagation vector will be altered a little bit, so that the incident angle of a light ray will gradually increase with each hit on the structured surface, until a condition for total internal reflection is not met, and the light is coupled out. An exemplary application of the illumination system is non-emissive displays.

However, a problem with the illumination system in WO2006/034831 is that the angular distribution of the out-coupled light may be large (wide). This is due to the structured surface pattern which has facet angles such that the beam width is changed upon out-coupling. As a result, the illumination system in WO2006/034831 is unsuitable for general illumination applications like office lighting, for which there usually is a requirement that the angular distribution or cut-off angle is limited to a certain value to avoid glare. For fulfilling the requirements for office lighting, collimation angles of typically 2x 45° FWHM (full width at half maximum) are required. In order to fulfill the glare requirements, the luminance for angles above 65° (i.e. the cut-off angle) should be below 1000 cd/m².

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to at least partly overcome this problem and to provide an improved light output system which in particular may fulfill requirements for general illumination like office lighting, as well as an improved light emitting device package that for instance can be used in such a light output system. These, and other objects that will be apparent from the following description, are achieved by a light emitting device package, a light output system, and a light output method according to the appended claims 1, 8, and 11, respectively.

According to one aspect of the present invention, there is provided a light emitting device package with an integrated collimating reflector, wherein a light emitting element is arranged in relation to the collimating reflector for producing collimated light.

"Collimating light" should in the context of the present invention be understood as limiting the angular distribution of light emitted by a light source. Also, the light emitting element may or may not form part of the package. Also, the collimating reflector preferably defines a cavity or the like in which the light emitting element may be received.

Since the collimating function is inherently incorporated into the present package, no additional collimating means outside the package are necessary, which for instance may simplify the construction of a system where packages of the present aspect are used. Also, there is no need of aligning any further collimating means, which aligning usually is problematic, and may degrade the overall light output performance if not carried out correctly.

In one embodiment of the present invention, the collimating reflector of the package comprises reflective walls configured at an angle of more than 65 degrees but not more than about 80 degrees (65° < wall angle < 80°), preferably about 75 degrees, in relation to a base plane of the light emitting device package. This results in a compact design of the collimating reflector and thus of the package, while a desired cut-off, e.g. 65 degrees or less, still can be guaranteed. Alternatively, the collimating reflector may have a cone- or CPC (compound parabolic concentrator) shape, for example. A beam "cut-off angle" may generally be defined as the angle, measured from the principal axis of the intensity of a light source, at which the light source cannot be seen, or at least is significantly reduced in intensity.

Further, in one embodiment, the collimating reflector of the package comprises an electrically conductive first portion and an electrically conductive second portion electrically insulated from the first portion, the portions together defining a collimating cavity in which the light emitting element is arranged, and wherein the light emitting element has a first bottom contact connected to one of said portions and a second bottom contact connected to the other one of said portions. Thus, each portion beneficially functions both as part of the reflector and as an electrical connection device for the light emitting element, realizing an uncomplicated and easy to assemble package with few parts. The light emitting element is preferably a flip type chip with each electrical contact directly connected to one of the two portions of the reflector. This contacting can be done by soldering or any other means to make electrical connections. Further, the two portions are preferably made of metal having both the conductive and reflective properties, removing the need of applying any mirror coating or the like to achieve the reflective property (which nevertheless is an option). Further, the two portions can be joined in an insulated manner by for instance a non-conducting glue.

In another embodiment, the collimating reflector further comprises a heat conductive third portion thermally connected to the light emitting element. The heat conductive third portion may for instance be arranged between the two electrically conductive portions, and allows good thermal management of the light emitting element.

Further, in one embodiment, an outer area of the first portion of the collimating reflector is adapted to be electrically contacted to an external entity, such as a printed circuit board (PCB), and an outer area of the second portion of the collimating reflector is adapted to be electrically contacted to an external entity, such as the PCB. "Outer area" refers here to a portion generally facing away from the collimating cavity, such as at an outer side or the bottom of the package. Since the first and second portions are electrically conducting, and electrically insulated from each other, they can be directly contacted or connected to a PCB or the like in a variety of ways, making the package very flexible and easy to mount. For instance, the bottom of each portion may be connected to a board, providing for a top-emitting light emitting device package emitting light in a main direction perpendicular to the board plane. On the other hand, the same package could without significant modification instead be mounted as a side emitting package, emitting light in a main direction parallel to the board plane, by mounting a side of the package exposing both the first and second portion to the board.

The above light emitting element is preferably a light emitting diode (LED) chip, and the light emitting device package is (thus) an LED package. It should be noted that more than one LED chip could be arranged in the collimating reflector (cavity), and that other suitable light emitting elements could be used. Further, the light emitting element(s) may be integrated into the light emitting device package.

According to another aspect of the present invention, there is provided a light output system comprising: at least one light emitting device package according to the above description, and an optical system comprising a light guide and at least one reflective out- coupling structure adapted to selectively couple light in-coupled to the light guide from the light emitting device package(s) out of the light guide, wherein the reflective out-coupling structure(s) is arranged such that a cut-off angle of a light beam produced by the light emitting device package(s) and in-coupled to the light guide is maintained when the beam is out-coupled from the light guide.

In other words, the optical system is angle conserving, meaning here that the angle distribution of light exiting the light guide is essentially the same as that of light produced by the package(s), though the main exit direction may be perpendicular to the main entry direction. Preferably, all reflective out-coupling structures of the optical system as well as any other reflective structures are angle conserving. Thus, according to the present aspect, an overall cut-off angle of the light output system is essentially determined by the cut-off angle of the light produced by the light emitting device packages(s), so as long as the cut-off angle of the packages(s) fulfills requirements for e.g. office lighting applications with respect to angular distribution, the complete light output system automatically also fulfils such requirements. This should be contrasted to WO2006/034831 wherein the specially structured surface pattern of the light guide does not maintain the angle, but instead alters it a little bit, as discussed above. Further, in the present aspect, the light from the packages(s) is first collimated and then spread out, while in e.g. WO2006/034831 the light is first spread out and may then be collimated (by means of one or two collimation films placed in front of the light out-coupling side). The former inventive solution allows for a more compact device, that is, small collimators within the light emitting device packages instead of one or more larger collimators for the (spreading and out-coupling) optical system as in the latter prior art solution. To maintain or conserve the beam cut-off angle, the at least one reflective out- coupling structure may for instance be oriented along a main direction of the beam, e.g. along the symmetry plane or axis of a symmetric light beam. In this case, the direction of the beam is not changed when the beam is reflected by the structure, and all angles of the beam's light rays with respect to the main direction stay within the same cone defined by the cut-off angle. Namely, such a structure only changes the sign of the direction component perpendicular to the main beam direction. If the beam's cross-section is not rotationally symmetric, e.g. the cut-off angle is different for the two main directions perpendicular to an elliptical beam direction, the reflecting structures should also be parallel with the planes of symmetry of the beam (e.g. the two main directions).

A reflective out-coupling structure not oriented as suggested in the previous paragraph may instead be arranged such that the beam when striking the structure is reflected in a direction essentially perpendicular or reversed to a main direction of the beam. Suitable reflecting structures include a reflecting structure perpendicular to the beam direction, that reverses the beam direction, and a structure at 45 degrees to the beam direction that produces a light beam in a direction orthogonal to the original beam direction. The latter is especially useful for coupling light out of the optical system, with maintained cut-off angle. Should the structure give different directions to different rays (e.g. like the specially structured surface pattern in WO2006/034831), this would cause beam broadening. With the light output system thus described it is possible to achieve an LED based, thin luminaire with an overall cut-off angle of 2 x 65 degrees or even less, making it suitable for use in general illumination, in particular office lighting where such a cut-off may be a requirement.

According to yet another aspect of the present invention, there is provided a method of outputting light, comprising the steps of: producing collimated light by means of at least one light emitting device package having an integrated collimating reflector in relation to which a light emitting element is arranged; and spreading light produced by the light emitting device package(s) and out-coupling the spread light from the device by means of an angle conserving optical system. This aspect exhibits similar advantages as the previously discussed aspects of the invention. Preferably, the angle conserving optical system comprises a light guide and at least one reflective out-coupling structure adapted to selectively couple light in-coupled to the light guide from the light emitting device package(s) out of the light guide, wherein the reflective out-coupling structure(s) is arranged such that a cut-off angle of a light beam produced by the light emitting device package(s) and in-coupled to the light guide is maintained when the beam is out-coupled from the light guide.

It is noted that the invention relates to all possible combinations of features recited in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing currently preferred embodiments of the invention. Figs. Ia-Ib are schematic perspective views of a luminaire according to an embodiment of the present invention.

Fig. 2a is a schematic cross-sectional side view of a variant of a light emitting device package for the luminaire of figs. Ia-Ib.

Fig. 2b is a schematic partly exploded perspective view of the package of fig 2a.

Fig. 2c is a schematic cross-sectional side view of another variant of a light emitting device package for the luminaire of figs. Ia-Ib.

Fig. 3a is a schematic side view of the package of figs. 2a-2b incorporated in a light guide of the luminaire of figs. Ia-Ib. Fig. 3b is a schematic top view of the package of figs. 2a-2b incorporated in a light guide of the luminaire of figs. Ia-Ib.

DETAILED DESCRIPTION

In the following description, terms like "top", "bottom" are mainly intended to define subject matter as it appears in the drawings and/or have a relative meaning, and do not necessarily reflect the positions and directions during actual use.

Figs. Ia-Ib illustrates a light output system 10, specifically a luminaire (that is, a (complete) lighting unit), according to an embodiment of the present invention. The present luminaire is suitable for use in general illumination, especially indoor lighting such as office lighting, since it features a limited output beam angle satisfying anti-glare requirements for such lighting applications.

The luminaire 10 comprises a light guide 12, preferably a thin light guide plate made of one or more pieces of dielectric material. Suitable dielectric materials include different transparent materials, such as various types of glass, poly-methyl methacrylate (PMMA), etc.

The luminaire 10 further comprises a plurality of light sources 14a- 14f located in corresponding in-coupling recesses 16a-16f in the light guide 12. The recesses 16a-16f may extend partly through the light guide 12, or be formed as through-going holes. The recesses 16 preferably have facets perpendicular to the plane of the light guide 12. The light sources 14 are adapted to emit collimated light in a number of main directions generally parallel to the plane of the light guide 12. In the luminaire 10 in fig. 1, each light source 14 comprises two unidirectional light emitting units arranged so as to function as side-emitters producing collimated light in two opposed main directions (i.e. along one axis parallel to the plane of the light guide). Each light source 14 may for instance comprise two top-emitters, for example light emitting diodes (LED), tilted about 90 degrees and arranged basically rear against rear. Alternative configurations include but are not limited to one collimated unidirectional LED per recess and four collimated unidirectional LEDs per recess, which four LEDs are arranged so as to produce light beams in four mutually perpendicular directions parallel to the plane of the light guide (i.e. along two orthogonal axes parallel to the plane of the light guide). Instead of LEDs, other collimated light emitting devices such as semiconductor laser diodes could be used as light sources. With respect to the expression "collimated" light, the LED packages are preferably adapted to produce a light beam within about 2 x 65 degrees (cut-off angle of 65°) in relation to the main emitting direction or optical axis of the package. Exemplary LED packages for the present invention will be explained further below with reference to figs. 2a-2c.

The luminaire 10 further comprises, adjacent to each in-coupling recess 16a- 16f, an associated out-coupling portion 18a-18f. Each of these out-coupling portions 18 in turn comprises four regions 20a-d arranged as mainly square or rectangular quadrants (with respect to the plane of the light guide 12) with the associated recess 16 in a central location. Further, the regions 20 have groove-shaped out-coupling structures 22 extending in the directions 45, 135, 225, and 315 degrees with respect to the centrally located recess 16. The out-coupling structures 22 are preferably specular grooves, having an essentially V-shaped cross-section with an opening angle of approximately 90°, arranged or formed for instance in the bottom surface of the light guide 12, forming specularly reflective surfaces tilted about 45 degrees with respect to the plane of the light guide 12. In the luminaire 10 in figs. Ia-Ib, the LEDs of the light sources 14a- 14f are oriented in such ways that the two main light emitting directions of each light source essentially coincide with directions of the out-coupling structures 22 in two of the regions 20a-d of the associated out-coupling portion 18a-18f. That is, for the exemplary light source 14e, one main light emitting direction coincides and runs parallel with the direction of the out-coupling structures 22 of the region 20a extending at 45 degrees, and the other opposite main light emitting direction coincides with the direction of the out-coupling structures 22 of the region 20c extending at 225 degrees.

The basis of operation of the luminaire 10 will now be explained with reference to the exemplary light source 14e. When the two LEDs of the light source 14e produce light, opposite collimated beams (e.g. 2 x 65 degrees light cone) 24a-24b are emitted from the light source 14e and in-coupled at the recess 16e through the vertical facets. As illustrated in fig. Ib for the beam 24a, the in-coupled light beam 24a will encounter either parallel grooves 22a, which do not out-couple the light, or perpendicularly oriented grooves 22b, which may out-couple the light. The illustrated beam 24a is thus mainly out- coupled through the regions denoted 26 in the luminaire 10.

The light guide 12 of the luminaire 10 satisfies the requirements of an angle- conserving, light-spreading and out-coupling optical system according to the present invention: Firstly, an in-coupled light beam will travel a certain distance in the light guide 12 along parallel out-coupling structures 22a before it comes across perpendicularly oriented out-coupling structures 22b which may out-couple the beam, hence the light-spreading functionality. The light-spreading functionality may for instance be advantageous for color mixing (different colored light sources) or for providing a less intense light output. Secondly, the out-coupling is provided by the structures 22. The beams that are in-coupled mainly parallel to the plane of the light guide 12 are generally stopped from exiting the light guide 12 by total internal reflection (TIR) at the light guide-air interface. However, when striking the 45 degrees out-coupling structures 22 arranged basically perpendicular to the beam path, the beams are reflected or redirected so that they may overcome the TIR condition and exit the light guide, whereby light output essentially perpendicular (main direction) to the light guide plane is provided. Thirdly, with respect to angle-conservation, an in-coupled collimated light beam may encounter an out-coupling structure like structure 22a which is oriented along the main direction of the beam, i.e. parallel to the main beam direction. Such a structure 22a will upon reflection "fold" one part of beam onto another part of the beam (i.e. a left part is folded by a vertical structure to become a right part, or an upper part is folded by a horizontal structure to become a lower part), so that all angles of the beam's light rays with respect to the main direction stay within the original cone. An in-coupled collimated light beam may encounter also an out-coupling structure like structure 22b which is oriented at 45 degrees (side view) with respect to the main direction of the beam. Here, the direction of all rays of the beam is changed in the same way, whereby all deviations from the main direction of the beam are still conserved. Thus, the beam width is in the present luminaire conserved at out- coupling. Also, any structures perpendicular to the beam, for instance the outer edges of the light guide (side view), will simply reverse the beam direction with maintained angles spread. To this end, the outer edges could also be made reflective. Also, since the out-coupling structures 22 preferably are specular, that is, featuring mirror-like reflection without diffusion, there will be little or no change of beam angle upon reflection or redirection at the out-coupling structures 22 due to diffusion. Overall, the cut-off angle (e.g. A degrees) of the LED light sources 14 is maintained, whereby the above luminaire 10 may have a beam spread limited within e.g. 2 x A degrees, making it suitable for use in general illumination, in particular office lighting. It should however be noted that when light enters the light guide 12 via a vertical recess facet, the angle is changed according to Snell's law, but that will be reversed to the original angle when the ray leaves the light guide 12. For instance, for a light guide medium n = 1.5, the 65 degrees cut-off angle will inside the medium become about 37 degrees.

It should also be noted that many variants of the shown luminaire 10 are possible in order to achieve an optimal or desired illumination pattern. For instance, the various light sources can have different directions. Some can for instance be directed at 45 and 225 degrees as in fig. 1, while others are arranged at 135 and 315 degrees. Further, in a bidirectional light source, two LEDs may be arranged so as to produce light in perpendicular directions parallel to the plane of the light guide, e.g. at 45 and 135 degrees. Further, the unidirectional light sources in a luminaire may be arranged to in-couple in the same direction or in different directions into the light guide. Further, various combinations of the above set- ups are possible, for instance a luminaire with some four-beamed light sources and some uni- or bidirectional light sources.

It should further be noted that the luminaire 10 described above is generally illustrated in a simplified and schematic manner. In particular, a real luminaire typically has a larger number of light-sources. However, the embodiments disclosed herein should be sufficient for enabling a person skilled in the relevant art to make and use the present invention. An exemplary actual luminaire may for instance comprise 100 LED light sources arranged in a 10 x 10 array at a pitch of 4 cm in one direction, and 12.5 cm in the orthogonal direction, resulting in a 40 cm x 125 cm luminaire. Each LED may for instance produce 100 Im (lumen), resulting in an overall output of 10 klm (20 klm/m²). Figs. 2a-2b illustrate a variant of a light emitting device package 100 which for example could be used in an light output system like the above luminaire 10.

Basically, the package 100 comprises a cup-shaped collimating reflector 104 in which at least one light emitting diode (LED) chip 102 is placed. Specifically, the collimating reflector 104 comprises two opposite main portions 106a, 106b each shaped like a half-cup. Each portion 106a, 106b has at least one slanting or angled reflective inner wall 108 and a bottom section 110. The reflective inner walls 108, together with the bottom sections 110, define a collimating cavity 112 having a top exit aperture 114, and in which collimating cavity 112 the LED chip 102 is placed on the bottom sections 110. In fig. 2a, the exit aperture 114 as well as an area defined by the two bottom sections 110 are square- shaped, but they could have other shapes including rectangular and circular (the latter relates for example to a CPC- or cone-shaped reflector 104 (not shown)).

The two portions 106a, 106b are electrically insulated by a non-conducting connection 116, for instance a non-conducting glue, joining the two portions 106a, 106b together at a cut essentially halfway through the reflector 104. Further, the two portions 106a, 106b are preferably made of metal, for instance aluminum or silver (though silver needs a protective coating). Using such metal portions 106a, 106b may serve two purposes: firstly, the inner walls 108 (and bottom sections 110) may be reflective without having to be metallized (e.g. coated with a metal) or the like; and secondly, the portions 106a, 106b themselves may become electrically conductive and as a result serve as electrical connection devices for the LED chip 102.

For the latter, the LED chip 102 is preferably a flip chip type LED chip. "Flip chip" generally refers to direct contacting without wire bonds between electrical contact points on a semi-conductor chip (which is turned upside down) and corresponding points on an associated external circuitry, as appreciated by the skilled person. In accordance thereto, the LED chip 102 has at least two electrical contacts or contact points 118 on its bottom side, where each contact 118 is directly connected to one portion 106a, 106b. This contacting as illustrated by electrical connections 120a, 120b may be done by soldering or any other means to make electrical connections. The present light emitting device package 100 is beneficial in that it can be externally contacted at the bottom, but also at any of two sides, without any significant modification. In the former case, the underside of each conducting portion 106a and 106b can be contacted at areas 121a and 121b (see fig. 2a), respectively, to for instance a printed circuit board, in which case the LED package may be mounted and function as a top emitter. In the latter case, a side of each conducting portion 106a and 106b can be contacted at areas 123a and 123b, or 123c and 123d (see fig. 2a), respectively, to for instance a printed circuit board (not shown), in which case the LED package 100 may be mounted and function as a side emitter. Thus, the same package may be contacted electrically from at least three sides. Upon operation of the LED package 100, electric signals are supplied to the reflector 104 for energizing the LED chip 102, whereupon the LED chip 102 emits light, which light is collimated by the reflector 104 towards an optical axis 122 of the package 100. Specifically, emitted light which is not already directed along the optical axis 122, for instance light rays emitted from the sides or edges or the LED chip 102, is reflected or redirected by the angled walls 108 back towards the optical axis 122, as illustrated by rays 124 in fig. 2a.

By appropriately sizing the cavity 112 and selecting an angle of inclination (denoted a) of the walls 108 in relation to a base plane 126, a desired cut-off angle (denoted b) of the package 100 may be achieved so that substantially no rays travel outside the imaginary cone 128. For a tapered air collimator with flat reflectors (e.g. reflector 104), the relation between inclination angle and cut-off angle can be expressed as: inclination angle = 45 degrees + (1/2) x cut-off angle. Preferably, the angle of inclination a is about 75 degrees, allowing the provision of a package 100 with a limited height, but still with a decent cut-off angle b, namely about 60 degrees. A cut-off angle of about 65 degrees (resulting in an overall "cut-off for the cone 128 of 2 x 65 degrees) likewise requires an inclination angle of about 77,5 degrees. Also, a collimating reflector with a cone-shaped cavity could in the same way benefit from having an angle of inclination of approximately 75 degrees. A CPC-shaped reflector can be more compact, but still reach the same cut-off angle, since the slope of such a reflector changes along the collimator. As indicated, more than one LED chip could be arranged in the collimating reflector 104. Further, phosphor could be applied over the LED chip for color conversion. The phosphor could be printed on the LED chip, or a ceramic conversion plate could be arranged in front of the LED chip, for example. Further, by centrally locating the LED chip 110 in a symmetric collimating cavity 112, a symmetric output beam may be provided. Fig. 2c illustrates another variant of an LED package. The package in fig. 2c is similar to that of figs. 2a-2b, and similar elements are therefore given the same denotation. A difference between the package of figs. 2a-2b and the package of fig. 2c is that the package 100 of fig. 2c further includes a third portion 130 arranged between the two portions 106a, 106b. The third portion 130 is made of a thermally conductive material, for instance aluminum, silver or copper, which copper may be coated with a reflective layer if it except for heat conduction also forms part of the reflective collimator. Just copper can be used if it only serves for heat conduction. Like in the previous variant, the portions 106a, 106b, and 130 are electrically insulated by means of non-conducting connections 116. A heat conducting, thermal connection 132 is further provided between the LED chip 102 and the third portion 130, for instance by means of metal soldering. The heat-conducting portion 130 and the thermal connection 132 serve to lead away heat from the LED chip 102 which it generates during operation. The heat may for instance be transported away to a larger heat sink (not shown). Removing heat from the LED chip during operation may promote color stability and increase the service life of the chip, as appreciated by the skilled person.

The LED package 100 incorporated in the light guide 12 of the luminaire 10 of figs. Ia-Ib is illustrated in figs. 3a-3b. Light leaving the LED chip 102 is collimated by the reflector 104 to a certain angle A. When the light enters the light guide 12 via a vertical facet of the recess 16, the angle is changed according to Snell's law (the medium changes from air to glass, for instance), but that will be reversed to the original angle when the ray leaves the light guide 12. An exemplary ray 28a (fig. 3a) is reflected by TIR in the horizontal light guide "ceiling" and then passes over structures 22b in the light guide "floor", and an exemplary ray 28c is reflected by a parallel vertical structure 22a (fig. 3b), for further transportation and spreading the light guide 12. Exemplary rays 28b, 28d are reflected by 45 degree out-coupling structures 22b in regions 26 (see fig. Ib) and on that occasion change direction so much that they overcome the TIR and exit the light guide 12. As best seen for ray 28b in fig. 3a, its main direction is changed from horizontal to vertical by the 45 degree out-coupling structure 22b, and upon leaving the light guide 12, angle A to the main vertical direction is equal to the original angle A to the main horizontal direction. Here it can be seen that the structures 22 are selective with respect to out-coupling, meaning that not every structure 22 out-couples every light beam or ray 28.

It should be noted that the light emitting device packages shown and discussed in relation to the figs. 2a-2c could be used separately, without the angle conserving optical systems, or in combination with some other optical system. For instance, in case the packages provide too collimated light for a luminaire, they can be used together with an optical system (for mixing and out-coupling) which is adapted to increase the angle spread to a desired value. Also, a light emitting element other than an LED chip could be used in the package. Also, the present light output system may be embodied with angle conserving optical systems other that the specific light guide assembly shown and discussed in relation to figs. Ia-Ib. For instance, a light guide having light sources arranged in a staggered pattern over the light guide plane, all light sources facing the same direction and being provided with an out- coupling facet in the opposite direction and having reflective side walls, is envisaged. Also, an exemplary reflecting out-coupling structure may have a height essentially equal to the light guide's thickness.

The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims.

Claims

CLAIMS:

1. A light emitting device package (100) with an integrated collimating reflector

(104), wherein a light emitting element (102) is arranged in relation to the collimating reflector for producing collimated light.

2. A light emitting device package according to claim 1, wherein the collimating reflector comprises reflective walls (108) configured at an angle of more than 65 degrees but not more than about 80 degrees, preferably about 75 degrees, in relation to a base plane (126) of the light emitting device package.

3. A light emitting device package according to claim 1 or 2, wherein the collimating reflector comprises an electrically conductive first portion (106a) and an electrically conductive second portion (106b) electrically insulated from the first portion, said portions together defining a collimating cavity in which the light emitting element is arranged, and wherein the light emitting element has a first bottom contact (120a) connected to one of said portions and a second bottom contact (120b) connected to the other one of said portions.

4. A light emitting device package according claim 3, wherein the collimating reflector further comprises a heat conductive third portion (130) thermally connected to the light emitting element.

5. A light emitting device package according to claim 3 or 4, wherein an outer area (121a, 123 a, 123 c) of the first portion of the collimating reflector is adapted to be electrically contacted to an external entity, such as a printed circuit board, and an outer area (121b, 123b, 123 d) of the second portion of the collimating reflector is adapted to be electrically contacted to an external entity, such as the printed circuit board.

6. A light emitting device package according to any one of the preceding claims, wherein the light emitting element is a light emitting diode (LED) chip, and the light emitting device package is an LED package.

7. A light emitting device package according to any one of the preceding claims, wherein the light emitting element is integrated into the light emitting device package.

8. A light output system, such as a luminaire (10), comprising: at least one light emitting device package (100) according to any one of the claims 1-7; and an optical system comprising a light guide (12) and at least one reflective out- coupling structure (22) adapted to selectively couple light in-coupled to the light guide from the light emitting device package(s) out of the light guide, wherein the reflective out-coupling structure(s) is arranged such that a cut-off angle of a light beam produced by the light emitting device package(s) and in-coupled to the light guide is maintained when the beam is out-coupled from the light guide.

9. A light output system according to claim 8, wherein the at least one reflective out-coupling structure comprises one reflective out-coupling structure oriented along a main direction of said beam.

10. A light output system according to claim 8, wherein the at least one reflective out-coupling structure comprises one reflective out-coupling structure arranged such that said beam when striking the one reflective out -coupling structure is reflected in a direction essentially perpendicular or reversed to a main direction of the beam.

11. A method of outputting light, comprising the steps of: producing collimated light by means of at least one light emitting device package having an integrated collimating reflector in relation to which a light emitting element is arranged; and spreading light produced by the light emitting device package(s) and out- coupling the spread light from the device by means of an angle conserving optical system.

12. A method according to claim 11, wherein the angle conserving optical system comprises a light guide and at least one reflective out-coupling structure adapted to selectively couple light in-coupled to the light guide from the light emitting device package(s) out of the light guide, wherein the reflective out-coupling structure(s) is arranged such that a cut-off angle of a light beam produced by the light emitting device package(s) and in-coupled to the light guide is maintained when the beam is out-coupled from the light guide.