Reducing thermal sensitivity of a lighting arrangement

Abstract

The invention relates to a lighting arrangement with at least one LED lighting element (15) arranged on a support member (12). An optical element (16) is arranged spaced from the LED lighting element (15) in a first direction O. A holder (14) is provided to hold the optical element (16) in a position relative to the LED lighting element (15). The holder (14) comprises at least a first holding portion (24a) extending from the support member (12) into the first direction O and a second holding portion (24b) connected to the optical element (16). The second holding portion (24b) is arranged such that at least a part extends into the first direction O. The second holding portion (26b) is spaced from the first holding portion (24a) in a direction traverse to the first direction O. In the case of distortions due to temperature changes and a mismatch of the coefficient of thermal expansion, the lighting arrangement minimizes variations in the displacement of the optical element (16) relative to the LED lighting element (15).

Claims

1. A lighting arrangement comprising: at least one light emitting diode (LED) lighting element arranged on a support member; an optical element arranged spaced from the LED lighting element in a first direction; and a holder to hold the optical element in a position relative to the LED lighting element, the holder comprising at least a first holding portion extending from the support member into the first direction and a second holding portion connected to the optical element arranged such that at least a part of the second holding portion extends into the first direction, wherein the second holding portion is spaced from the first holding portion in a direction traverse to the first direction, wherein the first holding portion and the second holding portion are connected by a first connecting portion arranged to form an angle with both the first holding portion and the second holding portion, wherein the first connecting portion is a plane wall element having a greater thickness than the first holding portion and the second holding portion, and wherein the optical element is one piece with the first holding portion and the second holding portion.

2. The lighting arrangement of claim 1, wherein the first holding portion extends into the first direction beyond the optical element.

3. The lighting arrangement of claim 1, wherein the first holding portion and the second holding portion are substantially parallel to each other.

4. The lighting arrangement of claim 1, wherein the first connecting portion extends substantially perpendicular to the first direction.

5. The lighting arrangement of claim 1, wherein the second holding portion is connected to the optical element by a second connecting portion extending substantially perpendicular to the first direction.

6. The lighting arrangement of claim 1, further comprising: a plurality of LED lighting elements arranged on the support member spaced apart from each other; and a plurality of optical elements arranged spaced apart from the plurality of LED lighting elements in the first direction, wherein the plurality of optical elements are connected to each other.

7. The lighting arrangement of claim 1, wherein the first holding portion and the second holding portion are plane wall elements.

8. The lighting arrangement of claim 1, wherein the first holding portion and the second holding portion surround the optical element.

9. The lighting arrangement of claim 1, wherein the holder is a box shaped housing comprising at least a pair of first housing walls parallel to each other and a pair of second housing walls parallel to each other, first housing walls and the second housing walls substantially perpendicular to each other.

10. The lighting arrangement of claim 1, wherein the holder element comprises a base portion and a clamp element affixing the base portion to the support member.

11. The lighting arrangement of claim 1, wherein the optical element comprises one or more of a collimator element and a lens element.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the drawings:

(2) FIG. 1 shows a perspective view of a first embodiment of a lighting arrangement;

(3) FIG. 2, 3 show a side view and a top view of the lighting arrangement of FIG. 1;

(4) FIG. 4 shows a longitudinal sectional view along B . . . B in FIG. 3;

(5) FIG. 5 shows a cross-sectional view along A . . . A in FIG. 2;

(6) FIG. 6 shows an enlarged view of the portion C in FIG. 5;

(7) FIG. 7 shows a partial cross-sectional view of a second embodiment of a lighting arrangement;

(8) FIG. 8 shows a partial cross-sectional view of a third embodiment of a lighting arrangement;

(9) FIG. 9a, 9b schematically show the structure of a holder according to a generic embodiment;

(10) FIG. 10a, 10b show the structure of a holder according to a comparative example,

(11) FIG. 11 shows a partial cross-sectional view of a fourth embodiment of a lighting arrangement.

DETAILED DESCRIPTION OF EMBODIMENTS

(12) A first embodiment of a lighting arrangement 10 shown in FIG. 1-3 comprises a support member, in the present example a base plate 12, onto which a plurality of light emitting diodes 15 see (FIG. 6not visible in FIGS. 1-5) and a holder 14 for a number of optical elements 16 are mounted. As the skilled person will understand, the base plate 12 shown is a simple an example of a support member suited for illustration of the holding function of the optical elements 16 relative to the base plate 12. In actual embodiments, the base plate 12 may e.g. be a circuit board. In more detailed embodiments, further components, not shown in the figures, may be arranged on the base plate 12, such as e.g. electronic components, conductor tracks, thermal interface elements and/or one or more heat sinks.

(13) As shown, the holder 14 is box-shaped to surround the optical elements 16. It has a surrounding flange 22, which is held down by a clamp 18 which may be fixed to the base plate 12 e.g. by a screw connection.

(14) FIGS. 4-6 show sectional views of the lighting arrangement 10. As shown in the enlarged view of FIG. 6, LEDs 15 are arranged on the base plate 12. Spaced by a small distance d in the direction of an optical axis O, the optical elements 16 are positioned. A plurality of LED elements 15 are arranged in a line on top of the base plate 12. As shown in FIG. 4, the optical elements 16 are each arranged in front of the individual LED elements 15.

(15) Each optical element 16 comprises a TIR collimator portion 16a arranged towards the LED elements 15 for receiving light therefrom and a lens portion 16b to emit the light as a shaped illumination beam into the direction of the optical axis O. In the example shown, the holder 14 is manufactured in one piece with the optical elements 16, made from a transparent material e.g. silicone.

(16) The LED elements 15 of the lighting arrangement 10 form an LED matrix, which may be e.g. used in automotive front lighting. In particular, the lighting arrangement 10 may be used for adaptive driving lighting, where the LEDs may be operated independently or in segments in order adjust the beam to a specific driving situation. As shown in the figures, in particular FIGS. 4-6, the optical elements 16 are each arranged in front of the LED elements 15. Distance d is preferably very small to allow good coupling of light from the LED element 15 into the TIR collimator portion 16a of each optical element 16.

(17) However, variations of the arrangement of the optical element 16 relative to the LED element 15, and in particular variations to the distance d, can significantly alter the output beam. A variation of the distance d may in particular alter the intensity of the output beam.

(18) FIG. 10a shows a schematic representation of a simple box-shaped holder 14 for positioning the optical element 16 relative to the LED element 15. In this comparative example, the holder 14 comprises on each side a first portion 24a extending straight into the direction of the optical axis O and a second portion 26 extending from the end of the first portion 24a at right angles up to the optical element 16.

(19) Assuming a significant CTE mismatch between the material of the holder 14 and the base plate 12 in the comparative example, a raised temperature will lead to distortions schematically shown in FIG. 10b. As illustrated, this will lead to a significant change in the relative arrangement of the LED element 15 and optical element 16, in particular with regard to the distance between these two elements.

(20) FIGS. 9a, 9b show a generic embodiment of a holder 14 for comparison. In the generic embodiment, the holder 14 comprises on both sides of the optical element 16 a first portion 24a extending into the direction of the optical axis O and a second portion 24b extending parallel thereto, but offset in traverse direction. The first and second holding portions 24a, 24b are connected by a first connection portion 26a extending at right angles to both the first and second holding portions 24a, 24b. The second holding portion 24b is connected to the optical element 16 by a second connecting portion 26b, also arranged at right angles with both the first and second holding portions 24a, 24b.

(21) As shown in FIG. 10a, the first holding portion 10a extends into the direction of the optical axis O beyond the optical element 16. The second holding portion 24b is arranged at a certain distance from the first holding portion 24a, but parallel thereto. The second holding portion 24b, the first connecting portion 26a and the upper part of the first holding portion 24a form a loop-like or spring structure on both sides of the optical element 16.

(22) In a case of increased temperature and severe CTE mismatch as shown in FIG. 9b, the holder 14 undergoes significant distortion, but this does not result in substantial changes in the positioning of the optical element 16. The angular relationship of the holding portion 24a, 24b and the connecting portions 26a, 26b may change and compressive stress in traverse direction may be generated in the optical element 16, but positioning of the optical element 16 with regard to the optical axis O remains relatively constant. The spring/loop structure at least partly compensates the deformation in the first holding portion.

(23) In the first embodiment of a lighting arrangement 10 shown in the sectional views of FIG. 4, 5, the holder 14 is comprised of plane wall elements comprising first (outer) holding portions 24a which extend straight into the direction of the optical axis O and second (inner) holding portions 24b arranged spaced therefrom in parallel. As in the generic embodiment of FIG. 9a, 9b, first connecting portions 26a are arranged in traverse direction to connect the first and second holding portions 24a, 24b, and second connection portions 26b are arranged to connect the second holding portions 24b to the optical element 16.

(24) FIG. 7, 8, 11 show alternative embodiments of lighting arrangements 10, which differ from the lighting arrangement 10 according to the first embodiment by the shape and arrangement of the first and second holding portions 24a, 24b.

(25) In the second embodiment according to FIG. 7, the first and second holding portions 24a, 24b are arranged at an angle of e. g. 30. In the third embodiment according to FIG. 8, the first and second holding portions 24a, 24b are connected by a curved portion.

(26) In the fourth embodiment according to FIG. 11, there are further holding portions 24c, 24d extending in parallel into the direction of the optical axis O besides the first and second holding portions 24a, 24b. All holding portions 24a-24d are arranged spaced from each other and are interconnected by perpendicular connecting portions. The holding portions 24a-24d are of different length, being shorter the closer they are to the optical element 16. Thus, a plurality of loop/spring structures is formed, which in the event of distortion due to CTE mismatch effectively compensates displacement in the direction of the optical axis O.

(27) For a CTE mismatch between the material of the base plate 12 with the material of the holder 14 and optical element 16, all of the described holding structures show an improved behaviour over the comparative example of FIG. 10a, 10b. Best results have been obtained with the holder 14 according to the first embodiment.

(28) While the invention has been illustrated and described in detail in the drawings and forgoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments.

(29) For example, while the above embodiments show a plurality of LEDs 15 in a line and correspondingly aligned optical elements 16, embodiments with only a single LED or optical element 16, or with other arrangements such as two-dimensional matrices of LED's and corresponding optical elements 16 may be provided. While the holder 14 and optical element 16 in the embodiments are provided as one piece, to be manufactured e.g. by injection moulding, alternative embodiments are conceivable with separate parts. Also, as illustrated by the different shapes shown in FIG. 7, 8, the specific shape of the first and second holding portions 24a, 24b may vary as long as at least a portion of both extends into the direction of the optical axis O, even if it is bent, rounded or inclined. Other variations to the disclosed embodiment can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure and the appended claims.

(30) In the claims, the word comprising does not exclude other elements, and the indefinite article a or an does not exclude a plurality.

(31) The mere fact that certain measures are recited in mutually different dependent claims or embodiments does not indicate that a combination of these measures cannot be used to advantage.

(32) Any reference signs in the claims should not be construed as limiting the scope.