Light emitting device having a mixing chamber

Abstract

The light-emitting device includes a mixing chamber (3). The mixing chamber has a bottom surface (11), a light-exit window (33), and at least one sidewall (32). The at least one sidewall extends between the bottom surface and the light-exit window. The light-emitting device further includes at least one light source (4) configured to emit light into the mixing chamber during operation. The at least one sidewall (32) has an inner surface (34) adjacent to the light-exit window (33) and facing the interior space (8) of the mixing chamber. The inner surface (34) is an asymmetric reflector (9) that reflects a greater amount of incident light back toward the bottom surface (31) than toward the light-exit window (33).

Description

[Technical Field]

[0001] The present invention relates to a light emitting device that includes a mixing chamber having a bottom surface, a light exit window, and at least one sidewall extending between the bottom surface and the light exit window, and at least one light source configured, in operation, to emit light into the mixing chamber. [Background technology]

[0002] To achieve high optical efficiency of the mixing chamber for the light emitting device, the sidewalls of these mixing chambers are typically white with high reflectivity, allowing the luminous flux reflected from the sidewalls of such mixing chambers to exit the mixing chamber at large angles, thereby increasing the brightness of the luminaire at large angles.

[0003] US 2016 / 369973 A1 describes a light emitting device in which individual light sources of the light emitting device are shielded to minimize the form factor and achieve a high degree of collimation. The light emitting device includes a plurality of light sources and first and second auxiliary optical components, each configured to emit light.

[0004] When used in an office environment, a luminaire should be office compliant. This means, for example, that the luminaire should have a Unified Glare Rating (UGR) below a certain limit. UGR is a method for calculating the glare caused by a luminaire, established by the International Commission on Illumination (CIE). UGR helps determine the likelihood that a luminaire will cause discomfort to those around it. Glare is a common problem in the workplace. For office work areas, UGR should be kept below 19, while in shared spaces such as hallways or breakout areas, it may vary between 19 and 25.

[0005] Office compliance can be achieved by using a clear optical cover and lens to reduce the angular output range of the light source. While this is highly efficient and meets standard requirements, such a luminaire will be perceived as a set of high-brightness spots. For a pleasant look and feel, the luminance of the light exit window should be as uniform as possible. This can be achieved by using a "milky" cover to provide a Lambertian distribution and a highly uniform light exit window. However, this may not comply with office regulations for a typical lumen output (e.g., 3500 lumens) and a typical surface area (e.g., 600 x 600 mm).

[0006] To simultaneously achieve office compliance and a pleasant look and feel, a highly reflective white mixing chamber and a diffuser foil or sheet placed directly below a less diffusive optical cover are typically used. The optical cover is typically made of clear or nearly clear optical material with optical structures to limit the light flux emitted at large angles. One example of an optical structure is black pigment, which may be added to the optical cover material to reduce glare, but black pigment has the disadvantage of reducing the efficiency of the lighting fixture. Glare reduction may also be achieved by reducing the reflectivity of the mixing chamber sidewalls, but this also has the negative side effect of reducing efficiency. Summary of the Invention [Problem to be solved by the invention]

[0007] The object of the present invention is to overcome these problems and to provide a light emitting device which overcomes or at least mitigates the problems of the prior art, thus reducing glare with no or little impact on efficiency. [Means for solving the problem]

[0008] According to a first aspect of the present invention, this and other objects are achieved by a light emitting device comprising a mixing chamber having a bottom surface, a light exit window, and at least one side wall extending between the bottom surface and the light exit window, and at least one light source configured to emit light into the mixing chamber in operation, wherein the at least one side wall borders the light exit window and has an inner surface facing the interior space of the mixing chamber, the inner surface being an asymmetric reflector that reflects a greater amount of incident light back towards the bottom surface than towards the light exit window.

[0009] Light exit window means in this context the area through which light from the mixing chamber can exit the mixing chamber.

[0010] The inner surface of the side wall is configured with an asymmetric reflector that reflects a greater amount of incident light back towards the bottom surface than towards the light exit window, thereby reducing the amount of light that leaves the mixing chamber at large angles, which leads to reduced glare. Furthermore, by returning the luminous flux towards the bottom surface, at least a portion of the luminous flux can be recycled, thereby maintaining a high efficiency of the light emitting device.

[0011] Among other things, it has been shown that in this way, a light emitting device can be provided in which the unified glare rating (UGR) is reduced to 19 or less, while maintaining efficiency close to 90%. In comparison, at least some of the prior art light emitting devices discussed above can in fact achieve a similar UGR, but with an efficiency on the order of only 60-70%. Thus, a light emitting device is provided in which glare is reduced with no or little impact on efficiency.

[0012] A light beam exiting the mixing chamber at a large angle means in this context that the light beam exits the light exit window at an angle of 65° or more, where the angle is the angle between the normal to the light exit window and the exiting light, and therefore an angle of 0° if the light exits parallel to the normal to the light exit window, i.e. perpendicular to the light exit window.

[0013] In one embodiment, the asymmetric reflector is a retroreflector.

[0014] The retroreflector achieves the objectives of the present invention by reducing the large angle luminous flux while allowing for recycling of the luminous flux.

[0015] In one embodiment, the inner surface is at least partially coated with an asymmetric optical coating.

[0016] An asymmetric optical coating should be understood in this context as a coating that provides that the angle of incidence of a light ray is different from the angle of reflection of the light ray.

[0017] The use of an asymmetric optical coating on the inner surface of the mixing chamber provides a simple solution that can reflect a greater amount of incident light towards the bottom surface than towards the light exit window. Additionally, the use of a coating can eliminate the need for structural changes to the mixing chamber to achieve the desired reflectivity, thereby keeping the manufacturing of the mixing chamber simple.

[0018] In one embodiment, the light emitting device includes an asymmetrical optical element, the asymmetrical optical element being disposed on an inner surface of at least one sidewall of the mixing chamber.

[0019] The asymmetric optical element may be, by way of non-limiting example, a retroreflective glare shield, a retroreflective cup, or a retroreflective lamellae. The asymmetric optical element achieves the objectives of the present invention by reducing large angle light flux while allowing light flux recycling.

[0020] In one embodiment, the light emitting device includes at least two light sources.

[0021] By including two light sources in the light emitting device, a more uniform luminous flux emitted by the light emitting device can be achieved. Of course, the light emitting device may include three, four, five or more light sources depending on the requirements imposed on the light emitting device.

[0022] In one embodiment, the light emitting device further comprises an optical cover, the optical cover being disposed on or defining at least a portion of a light exit window of the mixing chamber.

[0023] The optical cover may allow for further modulation, such as diffusion or directional control, of the light emitted from the light emitting device.

[0024] In one embodiment, the optical cover is made from an optically clear material.

[0025] By providing an optically transparent optical cover, protection of the mixing chamber and light source is achieved without unnecessary modulation of the light emitted from the light emitting device. The optically transparent optical cover protects the mixing chamber and light source from dust or other foreign matter, thereby preventing the foreign matter from contaminating and / or damaging the interior space of the light emitting device. Furthermore, the optically transparent optical cover ensures that no unnecessary light loss occurs when light passes through the optical cover.

[0026] In one embodiment, the optic cover comprises a microlens optic cover.

[0027] A microlens optical cover refers to an optical cover that includes at least one lens, and typically an array of lenses, with the lens diameter being 1 mm or less.

[0028] A microlens optical cover may be used to achieve uniform illumination from the light emitting device, and may also be used to collimate the light exiting through the light exit window.

[0029] In one embodiment, the light emitting device further comprises a diffusive foil.

[0030] The diffusing foil helps to achieve uniform illumination from the light emitting device.

[0031] In one embodiment, the diffusion foil is positioned at a distance from the light exit window of the mixing chamber towards the bottom surface of the mixing chamber.

[0032] Positioning the diffusion foil away from the light exit window ensures that large angle light flux transmitted through the diffusion foil is reflected from the sidewall before exiting the light exit window, rather than being transmitted at large angles through the light exit window.

[0033] In one embodiment, the light-emitting device further comprises at least one flange, which protrudes inward from the side wall towards the central axis of the mixing chamber, and which covers or defines a portion of the light-exit window, in other words, the flange thus extends parallel to the light-exit window.

[0034] This can further reduce glare without significantly affecting the efficiency of the light emitting device.

[0035] According to a second aspect of the present invention, this and other objects are achieved by a luminaire, light fixture or lamp comprising a light-emitting device according to the present invention.

[0036] According to a third aspect of the present invention, this and other objects are achieved by a luminaire, lighting fixture or lamp for use in an office environment, comprising a light-emitting device according to the present invention.

[0037] The present invention relates to all possible combinations of features recited in the claims. Other objects, features, and advantages of the inventive concept will become apparent from the following detailed disclosure, from the appended claims, and from the drawings. Features described in connection with one embodiment may also be incorporated in other embodiments, and the advantages of such features are applicable to all embodiments in which they are incorporated. [Brief explanation of the drawings]

[0038] This and other aspects of the invention will now be described in more detail with reference to the accompanying drawings, which show one embodiment of the invention. [Figure 1] Two intensity distribution graphs or curves are shown, the first graph showing an intensity distribution suitable for office lighting fixtures and the second graph showing an intensity distribution for a standard Lambertian intensity distribution. [Figure 2] 1 shows a schematic cross-sectional view of one embodiment of a light-emitting device according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0039] The present invention is described more fully hereinafter with reference to the accompanying drawings, in which presently preferred embodiments of the invention are shown. However, the present invention may 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, so that the scope of the disclosure will be fully conveyed to those skilled in the art.

[0040] Referring initially to Figure 1, two intensity distribution graphs or curves are shown: the first, graph 1, shows an intensity distribution suitable for an office lighting fixture according to the present invention, and the second, graph 2, shows the intensity distribution of a lamp having a standard Lambertian intensity distribution.

[0041] As shown in the second graph 2 of Figure 1, a lamp with a standard Lambertian intensity distribution exhibits an intensity distribution that is directly proportional to the cosine of the angle between the direction of the emitted light and the surface normal of the light-emitting surface. This means that the intensity distribution is greatest at an angle equal to zero, i.e., perpendicular to the light-emitting surface. Another characteristic of a lamp with a Lambertian intensity distribution is that it has the same radiance when viewed from any angle. In other words, the luminance of a lamp with a Lambertian intensity distribution is isotropic. The reason the radiance is the same from any angle is because, although the power emitted from a given surface element decreases by the cosine of the emission angle, the solid angle subtended by the surface of the surface element as seen by the observer also decreases by the same amount. Therefore, a problem arises with lamps with a Lambertian intensity distribution: glare. Because of the glare issue, Lambertian lamps are not suitable for use in office environments.

[0042] Instead, for an office environment, an appropriate intensity distribution is as illustrated in the first graph 1 of Figure 1. High intensity is experienced at small angles, with a rapid drop-off in intensity at large angles, thereby reducing glare from the office lighting fixture. This disclosure describes a lighting device 10 that is suitable for office environments.

[0043] 2, there is shown a schematic cross-sectional view of one embodiment of a light-emitting device 10 according to the present invention. The light-emitting device 10 includes a mixing chamber 3. The mixing chamber 3 has a bottom surface 31, a light exit window 33, and a sidewall 32. The mixing chamber 3 defines an interior space 8.

[0044] 2, the mixing chamber 3 has a generally cylindrical shape tapering towards the bottom surface 31 and thus has one circumferential side wall 32. However, the mixing chamber is not limited to this shape and it is within the scope of the present invention that the mixing chamber may take on any other shape, such as a box, pyramid, or sphere. The mixing chamber may also have more than one side wall 32, for example two, three, four, or more side walls.

[0045] The bottom surface 31 of the light-emitting device 10 shown in FIG. 2 is provided with two light sources 4. The light sources 4 may be LEDs. In operation, the light sources 4 may emit light of any color, such as white. The light sources 4 are configured to emit light into the mixing chamber 3 in operation. The light sources 4 are shown in FIG. 2 as being disposed on the bottom surface 31. However, it is also within the scope of the present invention for the light sources to be disposed on other surfaces of the mixing chamber 3. For example, the light sources may be disposed above the bottom surface 31, e.g., on an additional surface provided for this purpose, in an orientation such that the light sources emit light towards the bottom surface 31 in operation, whereby the bottom surface 31 acts as a secondary light source. Another possibility is that the mixing chamber may comprise an additional surface, e.g., a niche, for accommodating the light source(s).

[0046] The sidewall 32 of the mixing chamber 3 extends between the bottom surface 31 and the light exit window 33. If the mixing chamber has a substantially cylindrical shape, the mixing chamber may include only one sidewall 32. If the mixing chamber has another shape, the mixing chamber may include two or more sidewalls. The sidewall 32 has an inner surface portion 34 adjacent to the light exit window 33 and facing the interior space 8 of the mixing chamber 3. The inner surface portion 34 may be the entire inner surface of the sidewall 32, as long as it is the portion adjacent to the light exit window 33, or may be only a portion of the inner surface of the sidewall 32. The inner surface portion 34 is configured to reflect a greater amount of incident light from the light source 4 back toward the bottom surface 31 than toward the light exit window 33 using an asymmetric reflector 9. By reflecting a larger amount of incident light toward the bottom surface 31, where the light source 4 is located, rather than toward the light exit window 33, it is ensured that incident light reflected from the inner surface 34 does not exit the light exit window 33 at a large angle, for example, greater than 65°, thereby reducing glare. Different approaches may be used to achieve the desired reflectivity of the inner surface 34. One approach is to coat the inner surface 34 with an asymmetric optical coating, for example, a retroreflective coating. Another approach is to provide the inner surface 34 with one or more asymmetric optical elements, which are arranged on the inner surface 34 of at least one side wall 32 of the mixing chamber 3.

[0047] Furthermore, the light emitting device 10 shown in Fig. 2 includes an optical cover 7. The optical cover 7 is an optional element. The optical cover 7 may be disposed on the light exit window 33 and thus cover or define at least a portion of the light exit window 33 of the mixing chamber 3. In the embodiment shown in Fig. 2, the optical cover 7 covers or defines the entire light exit window 33. The optical cover 7 may be made of an optically transparent material, which allows light to pass through with minimal loss.

[0048] 2 further comprises a diffusion foil 5. The diffusion foil 5 is an optional element. The diffusion foil 5 is disposed at a distance from the light exit window 33 of the mixing chamber 3 in a direction towards the bottom surface 31 of the mixing chamber 3.

[0049] Furthermore, the light-emitting device 10 shown in FIG. 2 includes a flange 6. The flange 6 is an optional element. As shown in FIG. 2, one circumferential flange 6 is provided. Alternatively, the light-emitting device 10 may include two or more flanges, or multiple flange segments that together form a flange, which may be interrupted by spaces arranged at regular or irregular intervals. The flange 6 protrudes from the sidewall 32. The flange 6 protrudes toward the central axis A of the light-emitting device 10. The flange 6 is made of an optically opaque material. In the embodiment shown in FIG. 2, the flange 6 forms a rim that covers part of the light-exit window 33. Alternatively, the flange 6 may form part of the light-exit window 33. Thus, the flange 6 extends parallel to the light-exit window 33.

[0050] The light emitting device 10 may be provided in a lighting fixture, luminaire or lamp, which may be used in an office environment.

[0051] Those skilled in the art will recognize that the present invention is by no means limited to the preferred embodiments described above: on the contrary, many modifications and variations are possible within the scope of the appended claims.

[0052] Furthermore, variations to the disclosed embodiments can be understood by those skilled in the art, from a study of the drawings, the disclosure, and the appended claims, and can be implemented in practicing the claimed invention. In the claims, the word "comprises" does not exclude other elements or steps, and the indefinite articles "a" or "an" do 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 measures cannot be used to advantage.

Claims

1. a mixing chamber having a bottom surface, a light exit window, and at least one sidewall extending between the bottom surface and the light exit window; at least one light source configured, in operation, to emit light into the mixing chamber; 1. A light emitting device comprising: the at least one side wall has an inner surface adjacent to the light exit window and facing the interior space of the mixing chamber; the inner surface is an asymmetric reflector that reflects a greater amount of incident light back towards the bottom surface than towards the light exit window; A light emitting device, wherein the asymmetric reflector is a retroreflector, or the inner surface is at least partially coated with an asymmetric optical coating, or the light emitting device includes an asymmetric optical element, and the asymmetric optical element is positioned on the inner surface of at least one side wall of the mixing chamber.

2. 10. The light emitting device of claim 1, wherein the light emitting device comprises at least two light sources.

3. 3. The light emitting device according to claim 1, further comprising an optical cover, the optical cover being arranged on or defining at least a portion of the light exit window of the mixing chamber.

4. The light emitting device of claim 3 , wherein the optical cover is made from an optically transparent material.

5. 5. The light emitting device of claim 3 or 4, wherein the optical cover comprises a microlens optical cover.

6. 6. A light emitting device according to any one of the preceding claims, wherein the light emitting device comprises a diffusing foil.

7. 7. The light emitting device of claim 6, wherein the diffusion foil is positioned at a distance from the light exit window of the mixing chamber towards the bottom surface of the mixing chamber.

8. 8. The light-emitting device according to claim 1, wherein the light-emitting device comprises at least one flange, the at least one flange protruding inward from the at least one side wall towards the central axis of the mixing chamber, the at least one flange covering or defining a portion of the light exit window.

9. A lighting fixture, luminaire or lamp comprising a light-emitting device according to any one of claims 1 to 8.

10. 10. A luminaire, lighting fixture or lamp according to claim 9 for use in an office environment.

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