Patent Publication Number: US-2022214489-A1

Title: A light emitting device

Description:
FIELD OF THE INVENTION 
     The invention relates to edge lit light emitting devices. In particular, the invention relates to a light emitting device comprising at least one light source adapted for, in operation, emitting light, the at least one light source comprising a light emitting surface, and a light guide comprising a top surface, a bottom surface and a light incoupling edge extending between the top surface and the bottom surface, where a plane is defined as extending in parallel with the top surface and the bottom surface of the light guide, and where the at least one light source and the light guide being arranged in such a way with respect to each other that the light emitting surface of the at least one light source and the light incoupling edge of the light guide face each other. 
     BACKGROUND OF THE INVENTION 
     The edge-lit light guide architecture is commonly used in various forms of general lighting, such as for example recessed, surface mounted, and suspended luminaires. This architecture enables a very slim luminaire design, which is particularly suited for suspended luminaires with both direct and indirect lighting. The LED light sources are placed at the edge of the guide, where the light is coupled in. By means of extraction features on the guide, the light is coupled out. 
     Further advantages of this architecture are the uniform appearance of the light source, which is comfortable and aesthetically pleasing, and the low height of the luminaire, which allows for efficient logistic and elegant suspended luminaire designs. 
     To reduce the cost and weight of the light guide panel, and to reduce the luminaire thickness, the trend is to use thinner light guides. Typically, 6 mm light guides are not un-common in luminaires, while currently the trend is to use 4 or 3 mm thick light guides. The thickness of the light guide used is limited by the size of the LEDs. The edge of the light guide should be at least the size of the LED, to allow incoupling of the light. The size of the LED can also not be arbitrarily small, because the efficacy goes down rapidly in very tiny LED packages. 
     In general lighting, the mainstream LEDs used are mid-power LEDs that are typically 3×3 mm or larger (e.g. 3×5 mm or 5×7 mm). Smaller LED packages do exist, but these are either too expensive (e.g. high power LEDs) or not efficient enough (e.g. smaller mid-power packages or highly asymmetric packages like 1.5×3 mm) or they do not contain sufficient flux (e.g., two lines of low power LEDs do not produce enough flux for an edge-lit general lighting luminaire). 
     To reduce cost and weight of light guide based luminaires, and to reduce the luminaire thickness, it would be preferred to use light guides that are thinner than the smallest width of the LED light source. 
     An example of such a light emitting device is disclosed in EP 2 161 600 A1, where the light incoupling edges of the light guide are slanted, for instance by 45 degrees. The slanted incoupling edge provides a larger incoupling surface than the straight edge, for instance by a factor of the square root of 2 for a 45-degree slant, to accommodate incoupling LEDs with a larger width than the light guide thickness. 
     However, with such a light emitting device, a part of the light emitted by the light source, for instance a fraction of 1-1/√2 in the above-mentioned case of a 45-degree slant, cannot be coupled into the light guide. This fraction of the light is coupled out, mainly at the side of the light guide facing the slanted incoupling facet, and in an area close to the incoupling edge. 
     Also, for light emitting devices of the type disclosed in EP 2 161 600 A1, the ratio of upward flux and downward flux is a given constant. 
     Therefore, there is a desire to provide for a light emitting device with a light guide that is thinner than the smallest width of the LED light source, that also enables controlled light leakage, such that the leaked light can be used effectively, and that enables configuration of the ratio between light coupled out of the light guide in an upward and downward direction, respectively. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to overcome this problem, and to provide a light emitting device with a light guide that is thinner than the smallest width of the LED light source, and that also enables controlled light leakage, such that the leaked light can be used effectively, and such that configuration of the ratio between light coupled out of the light guide in an upward direction and a downward direction, respectively, is enabled. 
     A further object of the present invention is to provide a light emitting device having a reduced cost and weight as well as a reduced thickness. 
     According to a first aspect of the invention, this and other objects are achieved by means of a light emitting device comprising at least one light source adapted for, in operation, emitting light, the at least one light source comprising a light emitting surface, and a light guide comprising a top surface, a bottom surface and a light incoupling edge extending between the top surface and the bottom surface, a plane being defined as extending in parallel with at least one of the top surface and the bottom surface of the light guide, the at least one light source and the light guide being arranged in such a way with respect to each other that the light emitting surface of the at least one light source and the light incoupling edge of the light guide face each other, that the light incoupling edge of the light guide extends in a first angle, α, with respect to said plane, that the light emitting surface of the at least one light source extends in a second angle, β, with respect to said plane, and that at least one of the first angle, α, and the second angle, β, is less than 90°, and the light emitting device further comprising a linear refractive and/or reflective optical element arranged and adapted for shaping the fraction of the light emitted by the light source which is not coupled into the light guide and/or which leaks out of the top surface of the light guide into a focused light beam propagating above the top surface of the light guide in an acute angle with said plane. 
     It is noted that as used herein in connection with a refractive and/or reflective optical element, the term “linear” is intended to mean that the linear optical element in question is defined by its cross-section in such a way that the shape of the optical element does not change in the direction perpendicular to the said cross-section (i.e. along the line of light sources). Linearity of the optical element is important, because the position of a light source along the said direction is not defined. Such optical elements may be made through an extrusion process, but it can also be made through injection molding, or, for linear reflectors, plate bending. The production process, however, is not essential for the above definition of linearity, although extrusion is interesting because of the low costs associated therewith. 
     By providing that the light incoupling edge of the light guide extends in a first angle, α, with respect to the plane of the light guide, and that the light emitting surface of the at least one light source extends in a second angle, β, with respect to the plane of the light guide, a light emitting device is provided with which the ratio between light coupled out of the light guide in an upward and downward direction, respectively, may be configured as desired by choosing appropriate values for the first and second angles. 
     By furthermore providing for that the light emitting device comprises a linear refractive and/or reflective optical element arranged and adapted for shaping the fraction of the light emitted by the light source which cannot be coupled into the light guide, a light emitting device with which this fraction of the light can be used for indirect lighting, or to illuminate a reflective surface at a small distance from the light guide, is provided for. Thereby a fraction of light that would otherwise simply be lost is put to use in a simple and effective manner. 
     Thus, a light emitting device is hereby provided with which a light guide that is thinner than the smallest width of the LED light source may be used without compromising the light output if the light emitting device by losing light. Furthermore, such a light emitting device also enables controlled light leakage, such that the leaked light can be used effectively. 
     Also, such a light emitting device has a reduced cost and weight and thickness due to the possibility of using thinner light guides than otherwise possible. 
     Examples of linear refractive and/or reflective optical elements arranged and adapted for shaping the fraction of the light emitted by the light source which is not coupled into the light guide and/or which leaks out of the top surface of the light guide include a refractive lens, a prism, a TIR element and a reflector. 
     In practice about 33% of the light entering the light guide will eventually leak out of the top surface of the light guide. By providing a linear refractive and/or reflective optical element as described above, a light emitting device is provided with which these 33% of the light may be controlled and effectively be put to use by focusing it into a beam that is lightly tilted with respect to the plane of the light guide. Such a light emitting device thus provides both a direct and an indirect light output. 
     In an embodiment, the thickness, t of the light guide is smaller than the width, w, of the light emitting surface of the light source. 
     As also mentioned above, such a light emitting device has the advantage of a reduced production cost and a reduced weight and a reduced thickness due to the use of a thinner and thus smaller and lighter light guide than otherwise possible. 
     For instance, the thickness, t, of the light guide may be 2.2 mm, or even 2 mm, and wherein the width, w, of the light emitting surface of the light source may be 3 mm. 
     In an embodiment, the first angle, α is equal to 90°. 
     This provides for a light emitting device having a light guide of a particularly simple structure, thus keeping the costs even further down. 
     In an embodiment, the light emitting device further comprises optical elements or dots arranged and adapted for coupling light out of the light guide in a direction towards the bottom surface. 
     Thereby, a light emitting device is provided with which the light coupled out of the light guide in a downward direction and used for direct illumination may be provided with a Lambertian distribution. Depending on the optical elements provided, other beam shapes are also achievable. Examples of such optical elements are given further below in connection with  FIGS. 7A-E . 
     In an embodiment, the light emitting device comprises a reflector, a diffuse reflector, a reflective optical element or a retro-reflective optical element arranged and adapted for redirecting at least a part of the fraction of the light emitted by the light source and coupled out of the light guide though the top surface of the light guide in a direction back towards the light source. 
     Thereby, a light emitting device is provided with which further possibilities for configuring the ratio between light coupled out of the light guide in an upward and downward direction, respectively, is provided. In particular, a retro-reflective optical element has the additional advantage of avoiding unwanted leakage through the bottom surface of light guide altogether. 
     In an embodiment, the light emitting device further comprises a reflective plate element arranged at the top side of the light guide and adapted for redirecting the fraction of the light emitted by the light source and coupled out of the light guide though the top surface of the light guide in a downward direction. 
     Thereby, a light emitting device is provided with which simple Lambertian diffuse reflection in a downward direction may be obtained. Depending on the required shape of the downward beam and the optional beam shaping plate, such a reflective plate element may also be specular, patch-wise specular and diffuse, or glossy. 
     To enable configuring the ratio between light coupled out of the light guide in an upward and downward direction, respectively, the reflective plate element may also be partly transmissive, examples including a volume diffuser or a metallic reflector with perforated holes. 
     In an embodiment, the light emitting device further comprises light outcoupling elements arranged at or in the top surface of the light guide at or adjacent to the light incoupling edge of the light guide. 
     Thereby, a light emitting device is provided with which further possibilities for configuring the ratio between light coupled out of the light guide in an upward and downward direction, respectively, is provided for. 
     In an embodiment, at least the light emitting surface of the at least one light source is slanting with respect to said plane. 
     Thereby, a light emitting device is provided with which a larger incoupling surface than for an incoupling edge arranged in a right angle with the plane of the light guide is obtained. For instance, for a slant of 45°, the area of the light incoupling edge is increased by a factor of the square root of 2. Thereby it becomes possible to accommodate light sources with a light emitting surface having with a larger width, w, than the light guide thickness, t. 
     In an embodiment, both the light emitting surface of the at least one light source and the light incoupling edge of the light guide face is slanting with respect to said plane. 
     Thereby, a light emitting device with a simple construction and which is simpler to assemble is provided for. 
     In an embodiment, the first angle, α, is different from the second angle, β. 
     Thereby, a light emitting device is provided with which it becomes possible to obtain an upward directed light output with the desired broad, wide-angle distribution while simultaneously obtaining a downward directed light output with a reduced flux compared to when the first and second angles are chosen to be identical. 
     In an embodiment, the first angle, α, lies in the interval of 90°≥α≥0°. In another embodiment, the first angle, α, lies in the interval of 90°≥α≥45°. 
     For instance, if the first angle is chosen to be 45°, it becomes possible to use a light source with a light emitting surface having a width, w, of 3 mm and a light guide having a thickness, t, of only 2 mm. 
     In an embodiment, the second angle, β, lies in the interval of 90°&lt;β≥0°. In another embodiment, the second angle, β, lies in the interval of 90°&lt;β≥45°. 
     The inventors have proven by way of simulation that if choosing the first and second angle, such that they each lie in the above indicated intervals, it becomes possible to obtain an upward directed light output with the desired broad, wide-angle distribution while simultaneously obtaining a downward directed light output with a suitably high flux for common practical applications. Furthermore, the simulations show that the ratio between light coupled out of the light guide in an upward and downward direction, respectively, can be configured by choosing the light guide incoupling edge angle, i.e. the first angle, α, while keeping the LED light emitting surface angle, i.e. the second angle, β, constant. Analogously, when keeping the light guide incoupling edge angle, α, constant, the ratio between light coupled out of the light guide in an upward and downward direction, respectively, can be configured by choosing the LED light emitting surface angle, β. Exemplary simulations are shown in the Figures and will be described further below. 
     In an embodiment, the at least one light source is mounted on the light incoupling edge of the light guide by means of a mechanical holding device in such a way that an air gap is formed between the light source and the light guide. 
     In an embodiment, the at least one light source is mounted on the light incoupling edge of the light guide by means of an optically transparent soldering. 
     In an alternative embodiment, the at least one light source is mounted on the light incoupling edge of the light guide by means of an optically transparent glue. 
     In an embodiment being alternative or additional to the two above embodiments, the at least one light source is mounted on the light incoupling edge of the light guide by means of a mechanical holding device. 
     Thereby, a light emitting device is provided with which it becomes possible to mount the light source with the light emitting surface in any desired first angle with the plane of the light guide in a particularly simple and straight forward manner irrespective of the size of the second angle. 
     A mechanical holding device has the further advantage of providing for a light emitting device with a particularly robust and stable structure, especially when combined with an optically transparent soldering or glue. 
     The invention furthermore, in a second aspect, concerns a lamp, a luminaire or a lighting fixture comprising a light emitting device according to the invention. Non-limiting examples of such lamps, luminaires and lighting fixtures are direct-indirect lighting luminaires, particularly suspended luminaires, for indoor or outdoor workspaces. 
     It is noted that the invention relates to all possible combinations of features recited in the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       This and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing embodiment(s) of the invention. 
         FIG. 1  shows a cross-sectional side view of a first embodiment of a light emitting device according to the invention. 
         FIG. 2  shows a cross-sectional side view of a second embodiment of a light emitting device according to the invention. 
         FIG. 3  shows a cross-sectional side view of a section of a third embodiment of a light emitting device according to the invention. 
         FIG. 4  shows a cross-sectional side view of a section of a fourth embodiment of a light emitting device according to the invention. 
         FIG. 5  shows a cross-sectional side view of a section of a fifth embodiment of a light emitting device according to the invention. 
         FIG. 6A  shows a perspective view of a sixth embodiment of a light emitting device according to the invention. 
         FIGS. 6B and 6C  shows a diagram illustrating the light intensity and of the illuminance, respectively, of a light emitting device according to  FIG. 6A . In  FIG. 6B  the radial axis denotes Candela of the light output as a function of angle of view, while in  FIG. 6C  the horizontal axis indicates the location at the light guide, and the vertical axis is the emitted light at that location. 
         FIGS. 7A-C  shows a perspective view, a cross-sectional side view and a bottom view, respectively, of a seventh embodiment of a light emitting device according to the invention. 
         FIGS. 7D and 7E  shows a diagram illustrating the light intensity and of the illuminance, respectively, of a light emitting device according to  FIGS. 7A-C . In  FIG. 7D  the radial axis denoted Candela of the light output as a function of angle of view, while in  FIG. 7E  the horizontal axis indicates the location at the light guide, and the vertical axis is the emitted light at that location. 
         FIGS. 8A and 8B  shows an enlarged section and a cross-sectional side view, respectively, of an eighth embodiment of a light emitting device according to the invention. 
         FIGS. 8C and 8D  shows a diagram illustrating the light intensity and of the illuminance, respectively, of a light emitting device according to  FIGS. 8A and 8B . In  FIG. 8C  the radial axis denoted Candela of the light output as a function of angle of view, while in  FIG. 8D  the horizontal axis indicates the location at the light guide, and the vertical axis is the emitted light at that location. 
         FIGS. 9A and 9B  shows an enlarged section and a cross-sectional side view, respectively, of a ninth embodiment of a light emitting device according to the invention. 
         FIGS. 9C and 9D  shows a diagram illustrating the light intensity and of the illuminance, respectively, of a light emitting device according to  FIGS. 9A and 9B . In  FIG. 9C  the radial axis denoted Candela of the light output as a function of angle of view, while in  FIG. 9D  the horizontal axis indicates the location at the light guide, and the vertical axis is the emitted light at that location. 
     
    
    
     As illustrated in the figures, the sizes of layers and regions are exaggerated for illustrative purposes and, thus, are provided to illustrate the general structures of embodiments of the present invention. Like reference numerals refer to like elements throughout. 
     DETAILED DESCRIPTION 
     The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the invention are shown. This 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. 
       FIG. 1  shows a cross-sectional side view of a first embodiment of a light emitting device  1  according to the invention. 
     Generally, and irrespective of the embodiment, the light emitting device  1  according to the invention comprises a light source  2  and a light guide  3 . 
     The light source  2  comprises a light emitting surface  21 . The light source  2  is adapted for, in operation, emitting light. The light emitted by the light source may be white light, although light of any other color is also feasible. In the embodiments shown in the drawings, one light source  2  is shown. However, it is also feasible that the light emitting device may comprise more than one, e.g. two or three, light sources  2 . The light source  2  is typically a LED. 
     The light guide  3  comprises a top surface  31 , a bottom surface  32  and a light incoupling edge  33  extending between the top surface  31  and the bottom surface  32 . The light guide  3  further comprises an end surface  34  opposite the light incoupling edge  33  and extending between the top surface  31  and the bottom surface  32 . Furthermore, a plane  4  is defined as extending in parallel with at least one of the top surface  31  and the bottom surface  32  of the light guide  3 . The plane  4  may be described as a longitudinal or longitudinally extending plane of the light guide  3 . Also, the plane  4  typically, but not necessarily, extends perpendicular to the end surface  34 . 
     Still generally, and irrespective of the embodiment, the light source  2  and the light guide  3  are arranged such that the light emitting surface  21  of the light source  2  and the light incoupling edge  33  of the light guide  3  face each other. Thus, the light emitting device according to the invention is an edge lit light emitting device. 
     The light incoupling edge  33  of the light guide  3  extends in a first angle, α, with respect to the plane  4 , and the light emitting surface  21  of the light source  2  extends in a second angle, β with respect to the plane  4 . As may be seen from  FIG. 1 , both the light emitting surface  21  of the light source  2  and the light incoupling edge  33  of the light guide  3  is slanting with respect to the plane  4 . 
     Furthermore, in the embodiment shown in  FIG. 1 , the first angle α and the second angle β is the same. By way of non-limiting examples, the first angle α may lie in the interval of 90°≥α≥0°, or in the interval of 90°≥α≥45°. For instance, the first angle α may be 10°, 30°, 45°, 60°, 80° or 90°. Likewise, by way of non-limiting examples, the second angle β may lie in the interval of 90°&gt;β≥0°, or in the interval of 90°&gt;β≥45°. For instance, the second angle β may be 10°, 30°, 45°, 60°, 80° or 90°. 
     The light guide  3  comprises a thickness t. The light emitting surface  21  of the light source  2  comprises a width w. Typically, for a light emitting device according to any embodiment of the invention, the thickness t of the light guide  3  is smaller than the width w of the light emitting surface  21  of the light source  2 . By way of a non-limiting example, the thickness t of the light guide  3  may be 2.2 mm, and the width w of the light emitting surface  21  of the light source  2  may be 3 mm. 
     Still generally, and irrespective of the embodiment, the light emitting device  1  further comprises an optical element  6  adapted for shaping the fraction of the light emitted by the light source  2  which cannot be coupled into the light guide  3  and/or which leaks through the top surface  31  of the light guide  3 . This fraction of the light amounts to about 33% of the total amount of light emitted by the light source  2 . The optical element  6  is a linear refractive optical element. Alternatively, or additionally, the optical element  6  is a linear reflective optical element. By way of examples, the optical element  6  may be a refractive lens, a prism, a TIR element or a reflector. The optical element  6  comprises a surface  61  which extends over a part of the top surface  31  of the light guide. The surface  61  may be a curved surface curving in a way suitable to reflect or refract light in a desired manner. The optical element  6  has a height h, the size of which is chosen to enable forming the surface  61  in such a manner as to obtain a desired light output. In a non-limiting example, the height h may for instance be 20 mm. 
     The light source  2  of the light emitting device  1  is mounted on the light incoupling edge  33  of the light guide  3  by means of an optically transparent soldering or an optically transparent glue  51 . 
       FIG. 2  shows a cross-sectional side view of a second embodiment of a light emitting device  100  according to the invention. The optical element  6  is not shown in  FIG. 2  for the sake of simplicity. The light emitting device  100  differs from that of  FIG. 1  described above in that the light source  2  of the light emitting device  100  is mounted on the light incoupling edge  33  of the light guide  3  by means of a mechanical holding device  52 . The mechanical holding device  52  is adapted for holding the light source  2  such that the light emitting surface  21  and the light incoupling edge  33  are abutting one another, and thus are in direct contact. In principle, the mechanical holding device  52  may also be adapted for holding the light source  2  such that the light emitting surface  21  and the light incoupling edge  33  are in indirect contact, e.g. such that a small gap is present between the light emitting surface  21  and the light incoupling edge  33 . 
     Furthermore, the light emitting device  100  comprises light outcoupling elements  11  or structures arranged at the top surface  31  of the light guide  3  adjacent to the light incoupling edge  33  of the light guide  3 . 
       FIGS. 3-5  show cross-sectional side views of a third, fourth and fifth embodiment, respectively, of a light emitting device  101 ,  102 ,  103  according to the invention. The light emitting devices  101 ,  102  and  103  each differ from those of  FIGS. 1 and 2  described above in virtue of the following features. 
     The mechanical holding device  52  and the optical element  6  are provided in one piece, thus providing for a simpler and more robust structure of the light emitting device  101 ,  102 ,  103 . 
     Furthermore, the light emitting devices  101 ,  102  and  103  each comprise a reflector  91 ,  92  and  93 , respectively. The reflectors  91 ,  92 ,  93  are provided to block at least a part of the light leaking out of the light guide  3  through the top surface  31  and redirecting the blocked light back towards the light source  2 . The reflector  91  of the light emitting device  101  shown in  FIG. 3  is a diffuse reflector dimensioned to completely block the light leaking out of the light guide  3  through the top surface  31 . The reflector  92  of the light emitting device  102  shown in  FIG. 4  is a diffuse reflector dimensioned to block a part of the light leaking out of the light guide  3  through the top surface  31 . The reflector  93  of the light emitting device  103  shown in  FIG. 5  is a retro-reflector element shaped and dimensioned to send a part of the light leaking out of the light guide  3  through the top surface  31  back towards the light source  2  in such a way that no leakage through the bottom surface  32  of the light guide  3  occurs. 
       FIG. 6A  shows a perspective view of a sixth embodiment of a light emitting device  104  according to the invention. The light emitting device  104  differs from those of  FIGS. 1-5  described above in virtue of the following features. 
     As an alternative to an optical element  6 , the light emitting device  104  comprises a reflective element or plate  7  arranged at the top surface  31  of the light guide  3 . The reflective plate  7  provides for simple Lambertian diffuse reflection of the light not being coupled into the light guide  3  as well as the light leaking out through the top surface  31  of the light guide. Thereby, a downward directed beam of light is obtained, while no light is directed upwards. Depending on the required shape of the downward beam and an optional beam shaping plate, the reflective element or plate  7  may also be specular, patchwise specular and diffuse, or glossy. To provide also an upward directed beam of light, and further to allow for configuring the ration between the downward directed beam and the upward directed beam, the reflective element or plate  7  may also be partly transmissive. For instance, the reflective element or plate  7  may be a volume diffuser or a metallic reflector with perforated holes). 
       FIG. 6B  shows a diagram illustrating the light intensity distribution of the light emitted by a light emitting device  104  according to  FIG. 6A .  FIG. 6C  shows a diagram illustrating the illuminance of the light emitted by a light emitting device  104  according to  FIG. 6A . These illustrations show that a light pattern with a wide intensity distribution of the light emitted in the downward direction may be obtained. 
     It is noted that the light redirection optics, i.e. the optical elements  6  and/or  7 , according to the present invention could be applied to a light guide  3  having a thickness t corresponding to the width w of the light outcoupling surface  21  of the light source  2 , but could also be applied to a light guide  3  with a thickness t being smaller than the width w of the light outcoupling surface  21  of the light source  2 . 
       FIGS. 7A-C  show different views of a seventh embodiment of a light emitting device  105  according to the invention. The light emitting device  105  differs from those of  FIGS. 1-6  described above in virtue of the following features. 
     A holder  52  and an optical element  6  is provided at each of the two opposite ends corresponding to the light outcoupling edge  33  and the end surface  34  of the light guide  3 . Thus, the light emitting device  105  also comprises two light sources  2 , one at each of the two opposite ends corresponding to the light outcoupling edge  33  and the end surface  34  of the light guide  3 . However, the two light sources  2  are not shown in  FIGS. 7A-C  for the sake of simplicity. In this case, both the light outcoupling edge  33  and the light emitting surface  21  of the light sources  2  are arranged in an angle of 45° with the plane  4 . In other words, both the first angle α and the second angle β are 45°. Similarly, the end surface  34  may also be arranged in an angle of 45° with the plane  4 . 
     Furthermore, as shown on  FIG. 7C  the light emitting device  105  comprises a pattern of dots  8  arranged on the light guide  3 . The pattern of dots  8  are arranged on the bottom surface  32  of the light guide. The pattern of dots  8  provide for outcoupling of light with a Lambertian pattern through the bottom surface  32  of the light guide. The dots  8  of the pattern of dots may be of identical size, such as for instance 1.25 to 1.5 mm in diameter. Alternatively, the dots  8  of the pattern of dots may be of varying size. In the embodiment shown in  FIG. 6C , the dots  8  vary in size from 1.5 m in diameter at the center of the pattern to 1.25 mm in diameter at the edge of the pattern. 
       FIG. 7D  shows a diagram illustrating the light intensity of the light emitted by a light emitting device  105  according to  FIGS. 7A-C .  FIG. 7E  shows a diagram illustrating the illuminance of the light emitted by a light emitting device  105  according to  FIGS. 7A-C . These illustrations show that a broad, wide-angled light pattern of the light emitted in the upward direction may be obtained, and that the downward flux equals 49% of the total flux outputted by the light emitting device  105 . In more precise figures, the light sources  2  provide an input of 2 lumens, and the light emitting device  105  provides a total output of 1.72 lumens, of which 0.84 lumens are emitted in a downward direction. 
     In the embodiment of  FIGS. 7A-E , the indirect lighting component, i.e. the light emitted upwards has an extreme batwing distribution as shown in  FIG. 7D . This enables a wide and even ceiling illuminance from a relatively short distance. The direct lighting component, i.e. the light emitted downwards, is Lambertian. 
     It is noted that generally other beam shapes are also possible, based on solutions known per se, such as light guides with outcoupling features like faceted structures, or controlled surface roughness or paint with specific scattering properties, optionally in combination with beam shaping plates below the light guide, like MLO or redirecting prism plates, or meso-optic foils. 
       FIGS. 8A-B  show different views of an eighth embodiment of a light emitting device  106  according to the invention. The light emitting device  106  differs from those of  FIGS. 1-7  described above in virtue of the following features. 
     A holder  52  and an optical element  6  is provided at each of the two opposite ends corresponding to the light outcoupling edge  33  and the end surface  34  of the light guide  3 . Thus, the light emitting device  106  also comprises two light sources  2 , one at each of the two opposite ends corresponding to the light outcoupling edge  33  and the end surface  34  of the light guide  3 . However, the two light sources  2  are not shown in  FIGS. 8A-B  for the sake of simplicity. 
     The light outcoupling edge  33  of the light guide  3  and the light emitting surface  21  of the light sources  2  are arranged in different angles with respect to the plane  4 . In other words, the first angle α is different from the second angle β. This is obtained in that, in addition to the holder  52 , an air gap is provided between the light source  2  and the light guide  3 , particularly between the light emitting surface  21  and the light incoupling edge  33 . Optionally, the light source  2  may further be mounted on the light guide  3  by means of an optically transparent soldering or glue  53  arranged in the gap—cf. in particular  FIG. 8A . In this way, in the embodiment shown, the first angle α is about 60°, and the second angle β is about 45°. Of course, any set of different first and second angles may be obtained in this manner. Similarly, the end surface  34  may also be arranged in an angle of 60° with the plane  4 . 
       FIG. 8C  shows a diagram illustrating the light intensity of the light emitted by a light emitting device  106  according to  FIGS. 8A-B .  FIG. 8D  shows a diagram illustrating the illuminance of the light emitted by a light emitting device  106  according to  FIGS. 8A-B . These illustrations show that a broad, wide-angled light pattern of the light emitted in the upward direction may be obtained, and that the downward flux is reduced to 42% of the total flux outputted by the light emitting device  106 , when compared to the results obtained for the embodiment according to  FIGS. 7A-E . In more precise figures, the light sources  2  provide an input of 2 lumens, and the light emitting device  106  provides a total output of 1.76 lumens, of which 0.74 lumens are emitted in a downward direction. 
       FIGS. 9A-B  show different views of a ninth embodiment of a light emitting device  107  according to the invention. The light emitting device  107  differs from those of  FIGS. 1-8  described above in virtue of the following features. 
     A holder  52  and an optical element  6  is provided at each of the two opposite ends corresponding to the light outcoupling edge  33  and the end surface  34  of the light guide  3 . Thus, the light emitting device  107  also comprises two light sources  2 , one at each of the two opposite ends corresponding to the light outcoupling edge  33  and the end surface  34  of the light guide  3 . However, the two light sources  2  are not shown in  FIGS. 9A-B  for the sake of simplicity. 
     The light outcoupling edge  33  of the light guide  3  and the light emitting surface  21  of the light source  2  are arranged in different angles with respect to the plane  4 . In other words, the first angle α is different from the second angle β. This is obtained in that, in addition to the holder  52  an air gap is provided between the light source  2  and the light guide  3 , particularly between the light emitting surface  21  and the light incoupling edge  33 . Optionally, the light source  2  may further be mounted on the light guide  3  by means of an optically transparent soldering or glue  53  arranged in the gap—cf. in particular  FIG. 9A . In this way, in the embodiment shown, the first angle α is 90°, and the second angle β is about 45°. In this particular embodiment, only the light emitting surface  21  of the light source  2  is thus slanted with respect to the plane  4 . 
       FIG. 9C  shows a diagram illustrating the light intensity of the light emitted by a light emitting device  107  according to  FIGS. 9A-B .  FIG. 9D  shows a diagram illustrating the illuminance of the light emitted by a light emitting device  107  according to  FIGS. 9A-B . These illustrations show that a broad, wide-angled light pattern of the light emitted in the upward direction may be obtained, and that the downward flux is reduced to 30% of the total flux outputted by the light emitting device  107 , when compared to the results obtained for the embodiments according to  FIGS. 7A-E  and  FIGS. 8A-D . In more precise figures, the light sources  2  provide an input of 2 lumens, and the light emitting device  107  provides a total output of 1.77 lumens, of which 0.54 lumens are emitted in a downward direction. 
       FIGS. 7A-9D  thus overall illustrate that the ratio between upward emitted light and downward emitted light can be adjusted as desired by adjusting the light guide incoupling edge  33  angle, i.e. the first angle α, while keeping the light source light emitting surface  21  angle, i.e. the second angle β, constant. Thus, increasing the first angle, α, while keeping the second angle, β, constant reduces the downward flux. Analogously, when keeping the light guide incoupling edge  33  angle, i.e. the first angle α, constant, the ratio between upward emitted light and downward emitted light can be adjusted as desired by adjusting the light source light emitting surface  21  angle, i.e. the second angle β. 
     Thus, the amount of light leakage, and thus the amount of light not coupled into the light guide  3 , and therefore the indirect lighting component, may be tuned by choosing a different either first angle or second angle. Alternatively, or additionally the amount of light leakage, and thus the amount of light not coupled into the light guide  3 , and therefore the indirect lighting component, may be tuned by increasing the distance between the light source  2  and the light incoupling edge  33  of the light guide  3 . However, increasing the said distance may cause a direction of emission of light deviating from the direction of the light that leaks via the light guide. Part of the indirect lighting component may therefore less controlled. 
     Another way to tune the ratio between upward emitted light and downward emitted light is to add light outcoupling features at or in the top surface  31  of the light guide  3 , close to the light outcoupling edge  33  of the light guide  3 . 
     We note that the invention is not limited to rectangular guides with two-sided light injection. For example, a circular light guide with one round slanted facet, or a rectangular light guide with slanted facets on all four sides are also embodiments of the invention. 
     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. 
     Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage.