LED strip configurtions for large area round luminaires providing homogeneous lighting

Abstract

The disclosure concerns a light-emitting module (100) comprising one or more flexible, elongated light-emitting diode, LED, strips (110) and a mixing chamber (150). Each LED strip comprises a first side (112) on which a plurality of LEDs (111) is mounted, a second side (113) opposite to said first side, and two lengthwise edges (114). The mixing chamber (150) is arranged to mix light emitted by said LEDs and comprises a base (151). One of the lengthwise edges (144) of each LED strip is arranged to face the base (151) of the mixing chamber. At least a portion of each LED strip (110) is bent (or folded) to extend radially from a center portion of the mixing chamber towards one or more outer points (132), so that the one or more light-emitting diode strips (110) together form a number N of elongated arms (130). Each elongated arm comprises two segments of the LED strip, where the segments form opposite sides of the elongated arm.

Claims

1. A light-emitting module comprising: one or more flexible, elongated light-emitting diode strips, each having a first side on which a plurality of light-emitting diodes is mounted, a second side opposite to the first side, and two lengthwise edges; a mixing chamber arranged to mix light emitted by the light-emitting diodes, the mixing chamber having a base; wherein one of the lengthwise edges of each of the one or more light-emitting diode strips is arranged to face the base of the mixing chamber; wherein at least a portion of each of the one or more light-emitting diode strips is bent to extend radially from a center portion of the mixing chamber towards one or more outer points, so that the one or more light-emitting diode strips together form a number N of elongated arms, wherein said number N is larger than or equal to 3, wherein each elongated arm comprises two segments of one of the one or more light-emitting diode strips, the segments forming opposite sides of the elongated arm, and wherein the one or more flexible, elongated light-emitting diode strips being a flexible, elongated light-emitting diode strip of which at least a portion is bent to extend radially from the center portion of the mixing chamber towards a number N of outer points, thereby forming the number N of elongated arms.

2. The light-emitting module of claim 1, wherein each lengthwise edge facing the base of the mixing chamber is arranged against the base or in proximity of the base.

3. The light-emitting module of claim 1, wherein at least a segment of at least one of the one or more light-emitting diode strips along an elongated arm of the light-emitting diode strip comprises a light-emitting diode pitch gradient, such that the light-emitting diode pitch decreases from the center portion towards the outer point of the elongated arm.

4. The light-emitting module of claim 1, wherein at least a section of at least one of the one or more light-emitting diode strips, between a first light-emitting diode and a second, successive light-emitting diode, is folded to shorten the pitch between the first light-emitting diode and the second light-emitting diode.

5. The light-emitting module of claim 1, wherein the light-emitting diodes on at least one of the one or more light-emitting diode strips are arranged so that the light-emitting diode strip comprises regions with light-emitting diodes and regions without light-emitting diodes, and wherein each region without light-emitting diodes is arranged along a side of an elongated arm facing a side of a neighboring elongated arm having light-emitting diodes.

6. The light-emitting module of claim 1, wherein two neighboring arms are arranged at an angle θ, wherein θ=360/N.

7. The light-emitting module of claim 1, wherein at least a portion of at least one of the one or more light-emitting diode strips is arranged along an arc of a circle between the outer points of at least two elongated arms.

8. The light-emitting module of claim 7, wherein at least one segment of the light-emitting diode strip, forming a side of an elongated arm from one of the at least (N - 1) mountain folds to one of the at least (N - 1) valley folds, is substantially straight, thereby forming a star-like shape.

9. The light-emitting module of claim 1, wherein the light-emitting diode strip is arranged with at least (N - 1) valley folds at the center portion of the mixing chamber, and at least (N - 1) mountain folds forming the N outer points.

10. The light-emitting module of claim 1, wherein, in at least a portion of an elongated arm, the two segments forming opposite sides of the elongated arm are glued together on the second side of the light-emitting diode strip.

11. The light-emitting module of claim 1, wherein the light-emitting diodes are arranged on at least one of the one or more light-emitting diode strips so that light-emitting diodes on the opposite sides of an elongated arm are interleaved.

12. The light-emitting module of claim 1, wherein the mixing chamber further comprises a semi-reflective light exit window at least partially transmissive for visible light, the semi-reflective light exit window being arranged to couple out light emitted from the plurality of light-emitting diodes and mixed within the mixing chamber.

13. The light-emitting module of claim 1, wherein the mixing chamber has a width (W1) and a height (H), and wherein an aspect ratio of the width (W1) and the height (H) is in the range of 8 to 60.

14. A method for producing a light-emitting module of claim 1, the method comprising: providing the mixing chamber; providing the one or more flexible, elongated light-emitting diode strips; arranging, for each of the one or more light-emitting diode strips, one of the lengthwise edges to face the base of the mixing chamber; and bending at least a portion of each of the one or more light-emitting diode strips to extend radially from a center portion of the mixing chamber towards one or more outer points, so that the one or more light-emitting diode strips together form the number N of elongated arms.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Exemplifying embodiments will now be described in more detail, with reference to the following appended drawings:

(2) FIGS. 1a-b show schematic illustrations of a light-emitting module in accordance with some embodiments;

(3) FIG. 2 shows schematic views of a part of a LED strip in accordance with some embodiments;

(4) FIGS. 3a-c illustrate LED strips adapted to be arranged at the base of a mixing chamber in accordance with some embodiments;

(5) FIGS. 4a-b illustrate folding of an LED strip, in accordance with some embodiments;

(6) FIGS. 5a-b show schematic views of a LED strip on, or in the proximity of, the base of a mixing chamber, in accordance with some embodiments;

(7) FIGS. 6a-b illustrate a LED strip having a LED pitch gradient, in accordance with some embodiments;

(8) FIG. 7 shows a LED strip being folded to create a LED pitch gradient, in accordance with some embodiments;

(9) FIGS. 8a-b illustrate a LED strip having regions with LEDs and regions without LEDs, in accordance with some embodiments;

(10) FIG. 9 shows a schematic view of an arrangement of a LED strip on, or in the proximity of, the base of a mixing chamber in which the LEDs on opposite sides of an elongated arm are interleaved, in accordance with some embodiments;

(11) FIG. 10 illustrates a LED strip arrangement in which the second side of the LED strip is glued together at the outer points of the elongated arms, in accordance with some embodiments;

(12) FIG. 11 illustrates a LED strip arrangement in which a lengthwise edge is arranged in proximity to the base of a mixing chamber, in accordance with some embodiments.

(13) As illustrated in the figures, the sizes of the elements and regions may be exaggerated for illustrative purposes and, thus, are provided to illustrate the general structures of the embodiments. Like reference numerals refer to like elements throughout.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(14) Exemplifying embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments are shown. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled person.

(15) Referring to FIGS. 1a-b, a light-emitting module according to some embodiments will be described.

(16) FIG. 1a shows a schematic view of a light-emitting module 100 in accordance with some embodiments. The light-emitting module 100 comprises a light-mixing chamber 150 having a base 151, a semi-reflective exit window 152 and a side-wall 153. The light-emitting module comprises also a flexible, elongated LED strip 110. The light-emitting module 100 has a width W1 and a height H. The semi-reflective exit window 152 is detached from the module 100 in order to show the inside of the mixing chamber 150. During operation, the exit-window 152 would be attached to the sidewall 153 of the module 100. The base 151 and the sidewall 153 of the light-emitting module 100 together form a cavity (or chamber/container) in which the LED strip 110 may be placed.

(17) FIG. 1b is a plan view of the inside of the mixing chamber. The LED strip 110 is shown to be arranged on, or in proximity of, the base 151 of the mixing chamber 150. The LED strip 110 comprises a plurality of LEDs 111. The LED strip 110 is folded to form elongated arms 130 which extend radially from a center portion of the base 151 towards a number N of outer points 132. In the present embodiment N=6. Each elongated arm 130 is composed of two segments 131 of the LED strip 110, which form opposite sides of the elongated arm 130.

(18) The base 151 of the mixing chamber 150 in the present light-emitting module 100 has a circular shape, which in combination with the circumferential side wall 153 gives the mixing chamber 150 a cylindrical shape. It will however be appreciated that the mixing chamber may have other shapes. In particular, the base 151 may for example have an oblong, elliptical, or oval shape.

(19) The base 151 and/or the sidewall 153 may have highly reflective inside surfaces. Highly reflective may mean that the reflectance is in the range 90-100%. For example, the reflectance may be higher than 92%. Specifically, the reflectance may be higher than 94%. More specifically, the reflectance may be higher than 95%.

(20) The arrangement of the LED strip 110 is such that a lengthwise edge of the LED strip 110 is arranged to face the base 151. Specifically, in the present embodiment, the LED strip 110 is arranged against the base 151. This leads to the plurality of LEDs 111 being arranged so that light emitted from the LEDs is directed towards the side wall 153 of the mixing chamber, i.e. in a direction substantially parallel to the base 151. The LEDs 111 may be top emitters, emitting light through a top surface. Such LEDs, in combination with the arrangement of the LED strip 110, may result in more LED light being directed substantially parallel to the base 151, which may in turn increase the uniformity of the light emitted by the light-emitting module.

(21) Further, the arrangement of the LED strip 110 places the LEDs 111 facing away from the elongated arms 130 on which they are arranged. As a result, light emitted by the LEDs 111 may be emitted into the mixing chamber 150 for mixing within the mixing chamber 150.

(22) The LEDs 111 may be white LEDs, i.e. LEDs emitting light with a correlated color temperature (CCT) in the range 2000-8000 K. Specifically, the LEDs 111 may be adapted to emit light in the CCT-range 2500-7000 K. More specifically, the LEDs 111 may be adapted to emit light in the CCT-range 2700-5000 K.

(23) The LEDs 111 may further be adapted to emit white light which is within 10 SDCM (Standard Deviation of Color Matching) from the black body locus (BBL). Specifically, the LEDs 111 may be adapted to emit white light which is within 8 SDCM of the BBL. More specifically, the LEDs 111 may be adapted to emit light within 5 SDCM of the BBL.

(24) Further, the LEDs 111 may have a color rendering index (CRI) of at least 80. Specifically, the LEDs 111 may have a CRI of at least 85. More specifically, the LEDs 111 may have a CRI of at least 88.

(25) In some embodiments, the number of LEDs on an elongated arm may be at least 5. Specifically, the number of LEDs on an elongated arm may be at least 8. More specifically, the number of LEDs on an elongated arm may be at least 10.

(26) The semi-reflective exit window 152 may be arranged on top of the mixing chamber 150 (for example in contact with the side wall 153, on the opposite side of the base 151), to couple out light emitted by the LEDs 111 and mixed within the mixing chamber 150. The semi-reflective window 152 may for example have a reflectance in the range 30-80% for light emitted by the LEDs, such that 30-80% of the light is reflected back into the chamber for further mixing. Specifically, the reflectance may be in the range 35-70%. More specifically, the reflectance may be in the range 38-65%. Even more specifically, the reflectance may be in the range 40-60%. In the present embodiment, the width W1 of the module 100 corresponds to the diameter of the base 151, and the height H corresponds to the height of the sidewall 153. In other embodiments, having differently shaped bases, the width W1 may refer to another widest dimension of the base. An aspect ratio (W1/H) of the width W1 and the height H may be in the range 8-60. More specifically, W1/H may be in the range 9-30. Most specifically, W1/H may be in the range 10-20.

(27) With reference to FIG. 2, a LED strip in accordance with some embodiments will be described.

(28) FIG. 2 shows two views of the same LED strip 110, like the one described with reference to FIG. 1, one seen at an angle from above, and another one seen from below. The LED strip 110 is elongated and flexible, in particular it is bendable (foldable). It comprises a first side (front side) 112 on which a plurality of LEDs 111 is mounted. It further comprises a second side (backside) 113, which is opposite to the first side 112. Connecting the first side 112 and the second side 113, along the elongation of the LED strip 110, are two lengthwise edges 114 which correspond to the thickness of the LED strip 110. When the LED strip 110 is arranged within a light-emitting module, such as the module 100 of FIG. 1a, one of the lengthwise edges 114 may be arranged to face, such as against or in proximity of, the base (151 in FIGS. 1a-b) of the mixing chamber.

(29) The plurality of LEDs 111 (in the figure represented by seven LEDs 111) may be arranged in one row on the first side 112 of the LED strip 110 in the direction of the longitudinal extension of the LED strip 110. In some embodiments, the LEDs 111 may be equidistantly arranged in one row. However, in some other embodiments, the distance between successive LEDs 111 may vary.

(30) The LED strip 110 has a width W2. The width W2 may be in the range 3-30 mm. Specifically, the width W2 may be in the range 5-25 mm. More specifically the width W2 may be in the range 6-20 mm. These widths may provide mechanical strength to the LED strip so it may be arranged as described above, while not obstructing the mixing of light within the mixing chamber.

(31) Differently specified, the width W2 may be smaller than the height of the mixing chamber (H in FIG. 1a). As an example, the width W2 and the height H (FIG. 1a) may fulfill the condition that 0.05H<W2<0.5H. Specifically, the width W2 and height H (FIG. 1a) may fulfill the condition that 0.1H<W2<0.5 H. More specifically, the relation between the width W2 and the height H (FIG. 1a) may fulfill the condition that 0.15H<W2<0.35H.

(32) With reference to FIGS. 3a-b, embodiments of LED strips having supports or other features for arranging a lengthwise edge against the base of a mixing chamber will be described.

(33) FIG. 3a is a cross-sectional view of a LED strip 310a, taken perpendicular to the extension of the LED strip 310a. The LED strip 310a is equivalent to the LED strip 110 as described with reference to FIG. 2, except that it has a first lengthwise edge 114, and a second lengthwise edge 314 which is adapted to be arranged on the base of a mixing chamber. The second lengthwise edge 314 comprises a support 315a to facilitate the arrangement of the second lengthwise edge on the base of a mixing chamber (such as the mixing chamber 150 described with reference to FIG. 1). The support 315a extends from the first side of the LED strip orthogonally (i.e. at 90°). However, in other embodiments, a support may extend from the second side of the LED strip or at both sides of the LED strip. Further, the angle at which the support extends from the LED strip may be larger or smaller than 90°. The support 315a may form part of the LED strip 310.

(34) FIG. 3b is an illustration of a LED strip 310b seen from the first side. The LED strip may be equivalent to the LED strip 310a. The LED strip 310b comprises five LEDs 111, and four supports 315b. It will be appreciated that the figure only shows a section of the LED strip. In this embodiment, the supports 315b extend at a right angle from the LED strip 310b. Each support 315b is arranged in between two successive LEDs 111. The supports 315b have a rectangular cross section.

(35) FIG. 3c is an illustration of another embodiment of a LED strip 310c which is equivalent to the LED strip 310b except that the supports 315c have triangular cross sections. One side of the triangular cross section is adapted to be arranged along the base of a mixing chamber, such as the mixing chamber 150 of FIG. 1.

(36) Embodiments of the LED strip 310a, 310b, 310c may comprise a plurality of supporting elements like the supports described above. For example, embodiments of the LED strip may comprise more than 20 supporting elements/features. Some embodiments of the LED strip may comprise more than 30 supporting elements. Some embodiments of the LED strip may comprise more than 40 supporting elements. Specifically, in some embodiments of the LED strip, the supporting elements may be arranged so that each elongated arm comprises a supporting element. Further, in some embodiments of the LED strip, each elongated arm may comprise a plurality of supporting elements.

(37) These embodiments show some examples of supports which may facilitate arrangement of an LED strip on the base of a mixing chamber. However, it will be appreciated that an LED strip in accordance with the various embodiments of the present disclosure may be arranged on the base of a mixing chamber without the aid of supports. For example, the arrangement may comprise some means of attachment, such as a mechanical means of attachment or an adhesive. Further, in some embodiments, the supports may be adapted to arrange the lengthwise edge of the LED strip at a distance from the base.

(38) In relation to FIGS. 4a-b, arrangements including folding/bending of the LED strip will be described.

(39) FIG. 4a illustrates the folding of an elongated, flexible LED strip 110 with a mountain fold 433 and with a valley fold 434. In a mountain fold 433, the LED strip 110 is bent so that the angle α between two segments of the first side of the LED strip 110, one on each side of the fold, is increased such that α>180°. A mountain fold 433, thus, results in an angle α, between two segments of the first side of the LED strip 110, which is larger than 180°.

(40) In a valley fold 434, the LED strip 110 is bent (folded) so that an angle β between two segments of the first side of the LED strip, one on each side of the fold, is decreased such that β<180°. A valley fold 434 results in an angle β, between two segments of the first side of the LED strip 110, which is smaller than 180°.

(41) FIG. 4b shows an example of an arrangement of a LED strip 110. Not to obscure the figure, the LEDs of the LED strip 110 are not shown. However, the LED strip 110 may be equivalent to any of the LED strip 110 as described with reference to FIG. 2. The arrangement is formed by alternatively making valley folds 434 (at the center of the shape, arranged at the center portion of the base of the mixing chamber) and mountain folds 433 (forming the outer points of the shape). The present shape has six valley folds 434 at the center of the shape, and five mountain folds 433 making up five of the six outer points, as one outer point is made up of a first end point 416 and a second end point 417 of the bent/folded portion of the LED strip 110, and thus does not have a fold. In other embodiments, the end points 416, 417 may be located along an elongated arm, or at the center portion of the folded shape.

(42) Segments 435 between a valley fold 434 and a mountain fold 433 may be substantially straight, as shown in the figure, giving the arrangement a star-like appearance.

(43) The elongated arms are arranged so that the angle θ between (the centers of) two neighboring elongated arms is 360/N, N=6 being the number of elongated arms, thus forming a star-like shape with evenly distributed arms.

(44) With reference to FIGS. 5a-b, different arrangements of a LED strip in which a portion of the LED strip is arranged along an arc of a circle will be described.

(45) FIGS. 5a-b are plan views of LED strips 510 arranged on, in the proximity of, or above, the bases 151 of mixing chambers of light-emitting modules 500a, 500b, the light-emitting modules 500a, 500b being equivalent to the light-emitting module 100 described in relation to FIG. 1, except that the LED strips 510 comprise first portions 518a, 518b and second portions 519. The first portions 518a, 518b are folded to extend as elongated arms from the center portions of the respective bases 151 towards a number of outer points 132. The second portions 519 are arranged along an arc of a circle. Specifically, the portions 519 are arranged along the inner surface of the circumferential sidewalls 153, so that the LEDs of the LED strip 510 in the second portion 523 face into the mixing chamber.

(46) In FIG. 5a, the folding/arrangement of the first portion 518a is such that there is a distance between the valley folds 534a at the center of the arrangement. As a result, the backsides (second sides) of the segments of the LED strip which make up opposite sides of an elongated arm are not in contact along the whole length of the elongated arm. Further, the LEDs on either side of an elongated arm are interleaved. Interleaving of the LEDs will be described with reference to FIG. 9.

(47) In FIG. 5b, the folding/arrangement of the first portion 518b is such that there is substantially no distance between the valley folds 534b at the center of the arrangement. The backsides (second sides) of the segments which make up opposite sides of an elongated arm are at least partially in contact. More specifically, opposite sides are in contact along the whole length of the elongated arm. This arrangement may provide an even more uniform lighting.

(48) With reference to FIGS. 6a-b, an embodiment of a LED strip comprising a LED pitch gradient will be described.

(49) FIG. 6a shows a portion of a LED strip 610. The LED strip 610 may be equivalent to the LED strip 110 described above with reference to FIG. 2, except that it comprises a first region 620a in which the LED pitch (i.e. the distance between two successive LEDs 111) decreases from left to right. The LED strip 610 further comprises a second region 620b in which the LED pitch increases from left to right. Each region 620a, 620b comprising a LED pitch may for example comprise at least 4 LEDs, between which the LED pitch (distance) increases or decreases. Specifically, each region 620a, 620b comprising a LED pitch may for example comprise at least 6 LEDs. More specifically, each region 620a, 620b comprising a LED pitch may for example comprise at least 7 LEDs.

(50) FIG. 6b shows the LED strip 610 being arranged on, or in the proximity of, the base 151 of a mixing chamber, which may be equivalent to the mixing chamber 150 described with reference to FIG. 1. The LED strip has been folded with a mountain fold between the first region 620a and the second region 620b, so that the regions together form an elongated arm. The LED pitch decreases along the elongated arm, from the center portion of the base towards the outer point of the elongated arm. In the outer regions of the elongated arms, in which the elongated arms are more distant from one to another, the LEDs are more closely arranged. Thus, with this arrangement, the emitted light may be more uniformly spread.

(51) With reference to FIG. 7, an embodiment in which a LED pitch gradient is provided by folding the LED strip will be described.

(52) FIG. 7 is an illustration of a segment of a LED strip 710, which is equivalent to the LED strip 110 described with reference to FIG. 2, in accordance with some embodiments. The segment of the LED strip comprises a first LED 711a and a second, successive LED 711b. An area of the LED strip 721 between the first LED 711a and the second LED 711b is folded to decrease the pitch between the two LEDs 711a, 711b. This technique of folding the LED strip between LEDs may be used to adjust the LED pitch gradient along an elongated arm of a LED strip. This technique maybe used to form a light-emitting module such as for example described with reference to FIG. 6b.

(53) With reference to FIGS. 8a-b, an embodiment in which the LED strip comprises regions with LEDs and regions without LEDs will be described.

(54) FIG. 8a illustrates a portion of an elongated, flexible LED strip 810. The LED strip 810 is similar to the LED strip 110 described with reference to FIG. 2 except that the LED strip 810 comprises a first region 822 with LEDs 111 and a second region 823 without LEDs.

(55) FIG. 8b illustrates the LED strip 810 being arranged on, or in the proximity of, the base 151 of a mixing chamber. During folding of the LED strip, a valley fold has been formed between the first region 822 with LEDs 111 and the second region 823 without LEDs. As a result, the first region 822 and the second region 823 form part of two neighboring elongated arms (i.e. two different elongated arms), such that they face one another. As can be seen, the second region 823 without LEDs is located in proximity of the center portion of the base from which the elongated arms extend, such that the second region 823 without LEDs is a region of the LED strip located close to a region of a neighboring arm 822 having LEDs. In the present embodiment, the absence of LEDs in some regions where the elongated arms are closer to one-another may contribute to a more uniform illumination.

(56) The length L2 of a region 823 without LEDs may be related to the length L1 of an elongated arm. For example, the relation between the length L2 of a region without LEDs and the length L1 of an elongated arm may be 0.4L1<L2<L1. Specifically, the relation may be 0.5L1<L2<L1. More specifically, the relation may be 0.7L1<L2<L1. Most specifically, the relation may be 0.9L1<L2<L1.

(57) Specified differently, the length L2 of a region 823 without LEDs may be at least 3 cm. Specifically, the length L2 of a region 823 without LEDs may be at least 4 cm. More specifically the length L2 of a region 823 without LEDs may be at least 5 cm. Even more specifically, the length L2 of a region 823 without LEDs may be at least 6 cm.

(58) With reference to FIG. 9, an arrangement of a LED strip having LEDs being interleaved along an elongated arm will be described.

(59) The light-emitting module 900 shown in FIG. 9 is equivalent to the light-emitting module 100 described with reference to FIG. 1 except that the LEDs 911a on one side of an elongated arm 930 and the LEDs 911b on the other (opposite) side of the elongated arm 930 are interleaved. As the LEDs 911a on one side of the elongated arm 930 are not placed at the same level (along the length of the elongated arm 930) as the LEDs 911b on the other side of the elongated arm 930, the heat development in the elongated arm may be more evenly spread out. This may lead to better thermal management.

(60) With reference to FIG. 10, an arrangement of a LED strip, in which the backsides of the LED strip (in the elongated arms) are glued together, in accordance with some embodiments, will be described.

(61) FIG. 10 is an illustration of a LED strip 110. In order not to obstruct the illustration, the LEDs of the LED strip are not shown. The LED strip is bent/folded into a star-shaped arrangement. In a portion of each formed elongated arm 1030 of the LED strip arrangement, the backsides of the segments forming the elongated arm 1030 are glued together using an adhesive 1035. In the figure, the adhesive is placed in the outer portions of the elongated arms. However, in other embodiments, adhesive may be placed in other portions (one or more portions) of the elongated arms, or along the entire elongated arms. Adhesive on the backsides of the LED strip may improve thermal management.

(62) With reference to FIG. 11, an embodiment wherein the LED strip is arranged with a lengthwise edge in proximity to the base of a mixing chamber, in accordance with some embodiments, will be described.

(63) The light-emitting module 1100 is equivalent to the light-emitting module 100 of FIG. 1a, except for that the LED strip 1110 is arranged with a small gap h between the base 1151 and the LED strip 1110. The LED strip 1110 in the present embodiment is attached at the inside of the sidewall 1153. The gap h is smaller than the height H of the mixing chamber 1150. Specifically, the gap h may be such that h<H/2. More specifically, the gap may be such that h<H/4. For example, the gap h may be smaller than 3 cm. Specifically, the gap h may be smaller than 1 cm. More specifically, the gap h may be smaller than 0.1 cm.

(64) 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. For example, the LED strip segments forming the elongated arms may be in part curved, bent or folded to provide different illumination. Further, the arrangement of the LEDs on the LED strip may be varied. The shape and reflectance of the mixing chamber may be altered.

(65) Although features and elements are described above in particular combinations, each feature or element can be used alone without the other features and elements or in various combinations with or without other features and elements.

(66) Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claims inventions, from a study of the drawings, the disclosure and the appended claims. In the claims, the word “comprising” does not exclude other elements, and the indefinite articles “a” or “an” do not exclude a plurality. The mere fact that certain features are recited in mutually different dependent claims does not indicate that a combination of these features cannot be used to advantage.