Patent Publication Number: US-2022221113-A1

Title: Led strip configurtions for large area round luminaires providing homogeneous lighting

Description:
TECHNICAL FIELD 
     The present disclosure generally relates to the field of solid state lighting, and more specifically to light-emitting modules comprising a flexible light-emitting diode strip and a mixing chamber. The disclosure further relates to methods for producing such light-emitting modules. 
     BACKGROUND 
     Today, the market presents a large variety of light-emitting modules comprising different types of light sources. A common requirement for many light-emitting modules is to be able to provide uniform illumination. 
     Light-emitting diode based lighting solutions are highly appreciated due to their energy efficiency, long lifetime and lower use of potentially harmful materials. As light-emitting diodes are point sources, however, these have shown to be problematic to provide uniform illumination. 
     Various approaches have been used in order to combine the energy efficiency of LED-based light-emitting modules with uniform illumination. Such approaches include structures which allow for coupling of LED light into solid waveguides. This solution may, however, lead to losses, as such solid waveguides may absorb light. Another solution has been to arrange a large number of LEDs at the bottom of a light-mixing chamber and provide a diffuser to spread the light evenly. However, using such a large number of LEDs may prove costly, and placing the LEDs closely may lead to excess heating. 
     In WO2015101547, a round light-mixing chamber with a diffusive exit window is combined with a set of LEDs arranged on the inside of the sidewall of the mixing chamber. This solution provides uniform illumination for smaller light-emitting modules. However, the ability to provide uniform lighting may decrease for larger area modules. 
     There is thus a need for alternative light-emitting modules able to provide homogeneous illumination. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to overcome at least some of the above mentioned drawbacks, and to provide improved light-emitting modules and/or an improved method for production of such light-emitting modules. 
     This and other objectives are achieved by means of a light-emitting module and a method as defined in the appended independent claims. Other embodiments are defined by the dependent claims. 
     According to a first aspect of the present disclosure, there is provided a light-emitting module comprising one or more flexible, elongated light-emitting diode (LED) strips and a mixing chamber. Each of the one or more LED strips comprises a first side (front side), a second side (backside) opposite to the first side, and two lengthwise edges. A plurality of LEDs is mounted on the first side of the LED strip. 
     The mixing chamber (light-mixing chamber) is arranged to mix light which is emitted by the LEDs. The mixing chamber has a base. One of the lengthwise edges of each of the one or more LED strips is arranged to face the base. 
     Further, at least a portion of each of the one or more LED strips is bent (or folded) to extend radially from a center portion of the chamber toward one or more outer points. Through the bending/folding, the one or more LED strips together form a number N of elongated arms, each elongated arm comprising two segments of one of the one or more LED strips. The two segments form opposite sides of the elongated arm. The number N of elongated arms is equal to or larger than 3. 
     In the light-emitting module according to the first aspect, each of the one or more LED strips is bent or folded to form one or more of the radially-extending elongated arms. Each of the radially-extending elongated arms may be formed by a different bent or folded LED strip. Alternatively, all of the radially-extending elongated arms together may be formed by one bent or folded LED strip. 
     In the light-emitting module according to the first aspect, the one or more flexible, elongated light-emitting diode strips may be 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. In other words, this light-emitting module comprises (i) a flexible, elongated light-emitting diode strip, 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, and (ii) a mixing chamber arranged to mix light emitted by the light-emitting diodes, the mixing chamber having a base. One of the lengthwise edges is arranged to face the base of the mixing chamber. At least a portion of each the light-emitting diode strip is bent to extend radially from a center portion of the mixing chamber ( 150 ) towards a number N of outer points, thereby forming a number N of elongated arms. Each elongated arm comprises two segments of the light-emitting diode strip, the segments forming opposite sides of the elongated arm. The number N is larger than or equal to 3. In this light-emitting module, there is at least one flexible, elongated LED strip, and this particular LED strip is bent or folded to form at least three elongated arms. 
     The light-emitting module is configured to emit light-emitting module light, which comprises light emitted by the LEDs of the LED strip and mixed within the mixing chamber. 
     The LEDs may be arranged in one row on the first side. The LEDs may be arranged at even distances on the LED strip. Alternatively, the distance between the LEDs may differ along the LED strip. The distance between two neighboring LEDs is referred to as LED pitch. It will be appreciated that the arrangement of the LEDs on the LED strip is such that each elongated arm comprises at least one LED. The LEDs may be arranged only on one side of an elongated arm, or on both sides. 
     LEDs are point-sources, that is, they provide light from a small area. Placing the LEDs in a mixing chamber may allow the light to reflect within the chamber and to be mixed. As the light from the plurality of LEDs is reflected and mixed within the mixing chamber, the light may become more randomly directed and, thus, the light emitted by the light-emitting module may become more homogeneous. 
     In some embodiments, every elongated arm may have substantially the same length. Alternatively, the length of the elongated arms may vary. Specifically, there may be a repeating pattern to the lengths of the elongated arms, for instance a pattern in which every other arm has a longer length, and every other arm has a shorter length. In other embodiments, the length of the arms is adapted to the shape of the base of the mixing chamber. 
     As an example, the length of an arm may be at least 10 cm. Specifically, the length of an arm may be at least 15 cm. More specifically, the length of an arm may be at least 20 cm. Even more specifically, the length of an arm may be at least 25 cm, such as for example 30 cm. 
     As an example, the LED strip may have a width (i.e. the width of the first side, the shortest distance between the lengthwise edges), in this disclosure denoted W2, that is in the range 3-30 mm. Specifically, the LED strip may have a width (W2) that is in the range 5-25 mm. More specifically the LED strip may have a width (W2) that is in the range 6-20 mm. Such LED strips may provide mechanical strength while not obstructing the mixing of light within the mixing chamber. 
     In other words, the width (W2) of the LED strip may be smaller than the height, in this disclosure denoted H, of the mixing chamber. As an example, the width of the LED strip (W2) and the height of the mixing chamber (H) may be such that 0.05H&lt;W2&lt;0.5H. Specifically, the relation between W2 and H may be such that 0.1H&lt;W2&lt;0.5 H. More specifically, the relation between W2 and H maybe such that 0.15H&lt;W2&lt;0.35H. 
     The arrangement of the LED strip with a lengthwise edge facing the base may result in that light is emitted from the LEDs towards a side wall of the mixing chamber, i.e. in a direction substantially parallel to the base. Such a configuration improves light-mixing within the chamber. Enhanced light-mixing may in turn contribute to a more uniform lighting. Specifically, the LEDs may be top emitters (i.e. LEDs emitting light through a top surface, and not through side surfaces). Such LEDs in combination with the arrangement of the LED strip as described above, may result in more LED light being directed substantially parallel to the base of the mixing chamber, which may in turn increase the uniformity of the light-emitting module light. 
     Folding one or more LED strips to extend as elongated arms from a center portion of the mixing chamber may provide a more homogeneous illumination from substantially round or oval light-emitting modules. Specifically, the center portion of the mixing chamber may the same as, or directly above, a center portion of the base. Further, smaller or larger modules providing uniform lighting may be achieved as the bending of the LED strip may result in shorter or longer elongated arms. 
     According to some embodiments, the lengthwise edge of the LED strip which is arranged to face the base of the mixing chamber may more specifically be arranged against the base. This may improve the stability of the arrangement. 
     According to some embodiments, the lengthwise edge facing the base may be arranged in proximity of the base, i.e. with a (small) gap between the base and the lengthwise edge facing the base. In proximity of the base may be understood as in the bottom half of the mixing chamber, or, even more specifically, in the bottom half of the bottom half (i.e. the bottom fourth) of the mixing chamber. For example, the gap may be smaller than 3 cm. Specifically, the gap may be smaller than 1 cm. More specifically, the gap may be smaller than 0.1 cm. 
     For example, the LED strip may be held in place using a structure which may be in contact with, or form part of, the base or a sidewall of the mixing chamber. Such holding means could for example comprise a pin. 
     Arranging the LED strip away from the base may result in less heat development, and thus a reduction in the necessity of cooling. Arranging the LED strip in proximity of the base may result in more light-mixing, and thus improved uniformity of the light emitted by the light-emitting module. 
     According to some embodiments, at least a segment of the LED strip may comprise a LED pitch gradient. The arrangement of the at least one segment may be such that the LED pitch decreases along the elongated arm from the center portion of the base towards the outer point. The at least one segment comprising the LED pitch gradient may be arranged along an elongated arm of the folded portion of the LED strip. 
     The elongated arms may become more distant from one-another as they extend further away from the center portion (of the base) of the mixing chamber. Decreasing the LED pitch, i.e. the distance between successive LEDs, may counteract the increasing distance between the elongated arms towards the outer points, and may thus provide a more uniform light distribution. 
     According to some embodiments, at least a section of the LED strip, between a first LED and a second, successive LED, may be folded in order to shorten the pitch between the first LED and the second LED. In these embodiments, a LED strip having an even pitch, which may be cheaper and/or easier to produce, may be used while still improving the uniformity of light by altering the LED pitch. 
     According to some embodiments, the LEDs may be arranged on the LED strip so that the LED strip comprises regions with LEDs and regions without LEDs. The bending of at least a part of the LED strip may be such that each region without LEDs may be arranged along a side of an elongated arm facing a side of a neighboring arm having LEDs. In other words, each region without LEDs faces a region with LEDs located along a neighboring elongated arm. 
     The length of an elongated arm may be denoted L1. The length of a region without LEDs, L2, may be related to L1 through 0.4L1&lt;L2&lt;L1. Specifically, the length of the region without LEDs may be related to L1 through 0.5L1&lt;L2&lt;L1. More specifically, the length of a region without LEDs may be related to L1 through 0.7L1&lt;L2&lt;L1 Most specifically, the length of a region without LEDs may be related to L1 through 0.9L1&lt;L2&lt;L1. 
     Specified differently, the length of a region without LEDs may be at least 3 cm. Specifically, the length of a region without LEDs may be at least 4 cm. More specifically, the length of a region without LEDs may be at least 5 cm. Even more specifically, the length of a region without LEDs may be at least 6 cm. 
     These embodiments may offer an alternate, or complementary, solution for providing a more uniform lighting. Further, arranging regions without LEDs in areas where the LEDs may otherwise, due to the bending of the LED strip, be more densely arranged may decrease excess heat in such areas. Further, having regions without LEDs facing regions with LEDs may ensure that no (or at least less) dark spots, i.e. spots not illuminated by the LEDs, are created. Arrangement of sections with and without LEDs may also aid in obtaining a more uniform lighting depending on the bending of the LED strip. For example, LED-free regions may be arranged in areas in which the distance between elongated arms is shorter and avoided in areas where the distance is longer. 
     According to some embodiments, the number N of elongated arms may be in the range 5-14. Specifically, the number N of elongated arms (and thus outer points) may be in the range 6-12. More specifically, N may be in the range 7-11. Even more specifically, the number N may be in the range 8-10. These ranges may provide a more uniform light-distribution and contribute to fewer dark spots on the light-emitting module. 
     According to some embodiments, the angle between two neighboring arms may be θ=360/N. Specifically, the angle between each pair of neighboring arms may be θ=360/N. This embodiment may provide a more uniform light distribution in that the arms are distributed evenly around 360° (i.e. the outer points are distributed along the circumference of a circle). 
     According to some embodiments, at least a portion of the LED strip may be arranged along an arc of a circle between the outer points of at least two elongated arms. It will be appreciated that the portion of the LED strip which is arranged along an arc of a circle comprises at least one LED. 
     According to some embodiments, the portion which is arranged along an arc of a circle may be arranged with its second side against a circumferential sidewall of the mixing chamber. Arranging the second side towards a circumferential sidewall may direct the LEDs inwards so that they face the interior of the mixing chamber. This may improve the uniformity of the light emitted by the LEDs into the mixing chamber, especially for larger modules where the LED strip along the sidewall complements the arrangement extending from the center portion of the base. 
     According to some embodiments, the LED strip may be arranged with at least N−1 valley folds at the center portion of the mixing chamber, and with at least N−1 mountain folds forming at least N−1 outer points. 
     In this disclosure, a valley fold is characterized by two segments of the LED strip, on either side of the fold, being folded so that the angle between their respective first sides decrease. In other words, in a valley fold, the LED strip is folded so that two segments of the LED strip, on the side having LEDs, approach one another. A valley fold results in an angle between the two first sides of the segments which is smaller than 180°. 
     A mountain fold is made by folding two segments of LED strip, on either side of the fold, so that the first sides of the segments are folded away from one another. A mountain fold results in an angle between the two first sides of the segments which is larger than 180°. The outer points of the LED strip arrangement may be defined by mountain folds. 
     According to some embodiments, at least one segment of the LED strip, which forms a side of an elongated arm from one of the mountain folds (i.e. outer points) to one of the valley folds (at the center portion of the base), is substantially straight. Alternating mountain and valley folds, with substantially straight segments in between, results in a star-like shape. Such a shape may provide improved light-homogeneity. 
     According to some embodiments, the two segments of the LED strip forming opposite sides of an elongated arm may, along at least a portion of the elongated arm, be glued together on their respective second sides. This embodiment may provide improved thermal management. 
     According to some embodiments, the LEDs may be arranged on the LED strip so that LEDs on opposite sides of the elongated arm are interleaved. In other words, there may be an offset in the direction of the extension of the elongated arm (i.e. towards an outer point), between the LEDs arranged along one side of the elongated arm and the LEDs arranged along the opposite side of the elongated arm. This embodiment may lead to improved thermal management, as the LEDs may be more evenly distributed along the arm. 
     According to some embodiments, the mixing chamber may further comprise a semi-reflective light exit window. The semi-reflective light exit window may be at least partially transmissive for visible light. Further, the light exit window may be arranged to couple out light which has been emitted by the LEDs and has been mixed within the mixing chamber. For example, the reflectance of the semi-reflective light exit window may be in the range from 30-80% for light emitted by the plurality of LEDs. 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%. 
     A semi-reflective light exit window may increase mixing of the light emitted by the LEDs, as some light is reflected back into the mixing chamber. Too high reflectance may result in a loss of efficiency. Increased mixing may allow the light-emitting module to provide a more uniform illumination. 
     According to some embodiments, the mixing chamber may have a width (e.g. a diameter or a longest side), in this disclosure denoted W1, and a height, H. An aspect ratio of the width and the height (i.e. W1/H) may be in the range 8-60. Specifically, the aspect ratio may be in the range 10-30. More specifically, the aspect ratio may be in the range 12-20. 
     Further, the width W1 may be larger than 20 cm. Specifically, the width W1 may be larger than 40 cm. More specifically, the width W1 may be larger than 50 cm, such as for example 60 cm. 
     Light-emitting modules are often mounted in ceilings or even recessed into ceilings. Thus, having a low height (H) is often desired. A large aspect ratio may allow a low height while still providing more illumination. However, if the height is too low, the mixing characteristics of the mixing chamber may be impaired, which could lead to a decrease in the uniformity of the illumination. 
     According to a second aspect of the disclosure, a method for producing a light-emitting module is provided. The method may result in a light-emitting module in accordance with any of the embodiments described in relation to the first aspect of the disclosure. The method comprises providing a mixing chamber having a base and providing one or more flexible, elongated light-emitting diode (LED) strips, each with a first side, a second side, and two lengthwise edges. On the first side, a plurality of LEDs is arranged. The LEDs may be arranged in one row on the first side. The LEDs may also be arranged at even intervals on the LED strip, or with varying intervals. 
     Further, the method comprises arranging, for each of the one or more LED strips, one of the lengthwise edges of the LED strip to face the base of the mixing chamber and bending at least a portion of each of the one or more LED strips to form a number N of elongated arms extending radially from a center portion of the chamber towards a number N of outer points. Each elongated arm comprises two segments of at least one of the one or more LED strips which form opposite sides of the elongated arm. 
     It is noted that other embodiments using all possible combinations of features recited in the above described embodiments may be envisaged. Thus, the present disclosure also relates to all possible combinations of features mentioned herein. Any embodiment described herein may be combinable with other embodiments also described herein, and the present disclosure relates to all combinations of features. In particular, it will be appreciated that the specific embodiments described with reference to the first aspect of the disclosure apply also to the method according to the second aspect of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplifying embodiments will now be described in more detail, with reference to the following appended drawings: 
         FIGS. 1 a - b    show schematic illustrations of a light-emitting module in accordance with some embodiments; 
         FIG. 2  shows schematic views of a part of a LED strip in accordance with some embodiments; 
         FIGS. 3 a - c    illustrate LED strips adapted to be arranged at the base of a mixing chamber in accordance with some embodiments; 
         FIGS. 4 a - b    illustrate folding of an LED strip, in accordance with some embodiments; 
         FIGS. 5 a - 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; 
         FIGS. 6 a - b    illustrate a LED strip having a LED pitch gradient, in accordance with some embodiments; 
         FIG. 7  shows a LED strip being folded to create a LED pitch gradient, in accordance with some embodiments; 
         FIGS. 8 a - b    illustrate a LED strip having regions with LEDs and regions without LEDs, in accordance with some embodiments; 
         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; 
         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; 
         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. 
     
    
    
     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 
     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. 
     Referring to  FIGS. 1 a - b   , a light-emitting module according to some embodiments will be described. 
       FIG. 1 a    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. 
       FIG. 1 b    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 . 
     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. 
     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%. 
     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. 
     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 . 
     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. 
     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. 
     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. 
     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. 
     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. 
     With reference to  FIG. 2 , a LED strip in accordance with some embodiments will be described. 
       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. 1 a   , one of the lengthwise edges  114  may be arranged to face, such as against or in proximity of, the base ( 151  in  FIGS. 1 a - b   ) of the mixing chamber. 
     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. 
     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. 
     Differently specified, the width W2 may be smaller than the height of the mixing chamber (H in  FIG. 1 a   ). As an example, the width W2 and the height H ( FIG. 1 a   ) may fulfill the condition that 0.05H&lt;W2&lt;0.5H. Specifically, the width W2 and height H ( FIG. 1 a   ) may fulfill the condition that 0.1H&lt;W2&lt;0.5 H. More specifically, the relation between the width W2 and the height H ( FIG. 1 a   ) may fulfill the condition that 0.15H&lt;W2&lt;0.35H. 
     With reference to  FIGS. 3 a - 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. 
       FIG. 3 a    is a cross-sectional view of a LED strip  310   a , taken perpendicular to the extension of the LED strip  310   a . The LED strip  310   a  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  315   a  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  315   a  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  315   a  may form part of the LED strip  310 . 
       FIG. 3 b    is an illustration of a LED strip  310   b  seen from the first side. The LED strip may be equivalent to the LED strip  310   a . The LED strip  310   b  comprises five LEDs  111 , and four supports  315   b . It will be appreciated that the figure only shows a section of the LED strip. In this embodiment, the supports  315   b  extend at a right angle from the LED strip  310   b . Each support  315   b  is arranged in between two successive LEDs  111 . The supports  315   b  have a rectangular cross section. 
       FIG. 3 c    is an illustration of another embodiment of a LED strip  310   c  which is equivalent to the LED strip  310   b  except that the supports  315   c  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 . 
     Embodiments of the LED strip  310   a ,  310   b ,  310   c  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. 
     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. 
     In relation to  FIGS. 4 a - b   , arrangements including folding/bending of the LED strip will be described. 
       FIG. 4 a    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&gt;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°. 
     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&lt;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°. 
       FIG. 4 b    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. 
     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. 
     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. 
     With reference to  FIGS. 5 a - 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. 
       FIGS. 5 a - 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  500   a ,  500   b , the light-emitting modules  500   a ,  500   b  being equivalent to the light-emitting module  100  described in relation to  FIG. 1 , except that the LED strips  510  comprise first portions  518   a ,  518   b  and second portions  519 . The first portions  518   a ,  518   b  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. 
     In  FIG. 5 a   , the folding/arrangement of the first portion  518   a  is such that there is a distance between the valley folds  534   a  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 . 
     In  FIG. 5 b   , the folding/arrangement of the first portion  518   b  is such that there is substantially no distance between the valley folds  534   b  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. 
     With reference to  FIGS. 6 a - b   , an embodiment of a LED strip comprising a LED pitch gradient will be described. 
       FIG. 6 a    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  620   a  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  620   b  in which the LED pitch increases from left to right. Each region  620   a ,  620   b  comprising a LED pitch may for example comprise at least 4 LEDs, between which the LED pitch (distance) increases or decreases. Specifically, each region  620   a ,  620   b  comprising a LED pitch may for example comprise at least 6 LEDs. More specifically, each region  620   a ,  620   b  comprising a LED pitch may for example comprise at least 7 LEDs. 
       FIG. 6 b    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  620   a  and the second region  620   b , 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. 
     With reference to  FIG. 7 , an embodiment in which a LED pitch gradient is provided by folding the LED strip will be described. 
       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  711   a  and a second, successive LED  711   b . An area of the LED strip  721  between the first LED  711   a  and the second LED  711   b  is folded to decrease the pitch between the two LEDs  711   a ,  711   b . 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. 6   b.    
     With reference to  FIGS. 8 a - b   , an embodiment in which the LED strip comprises regions with LEDs and regions without LEDs will be described. 
       FIG. 8 a    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. 
       FIG. 8 b    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. 
     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&lt;L2&lt;L1. Specifically, the relation may be 0.5L1&lt;L2&lt;L1. More specifically, the relation may be 0.7L1&lt;L2&lt;L1. Most specifically, the relation may be 0.9L1&lt;L2&lt;L1. 
     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. 
     With reference to  FIG. 9 , an arrangement of a LED strip having LEDs being interleaved along an elongated arm will be described. 
     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  911   a  on one side of an elongated arm  930  and the LEDs  911   b  on the other (opposite) side of the elongated arm  930  are interleaved. As the LEDs  911   a  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  911   b  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. 
     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. 
       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. 
     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. 
     The light-emitting module  1100  is equivalent to the light-emitting module  100  of  FIG. 1 a   , 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&lt;H/2. More specifically, the gap may be such that h&lt;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. 
     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. 
     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. 
     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.