Lighting device

Abstract

A lighting device (100) comprising: a light source (102) configured to emit light along an optical axis (L) from a light emitting region (102a) of the light source (102) towards a light exit window (104) of the lighting device (100); and a transreflective wall structure (106) for reducing glare of the light emitting region (102a) when viewed through the wall structure (106), the wall structure (106) surrounding the light emitting region (102a) and extending between the light emitting region (102a) and the light exit window (104) in a direction substantially parallel to the optical axis (L), wherein light emitted from the light emitting region (102a) comprises a direct portion propagating directly between the light emitting region (102a) and the light exit window (104) and a diverging portion incident on the inwardly facing surface (106 ') of the wall structure (106), and wherein the transreflective wall structure (106) is transparent and specularly reflective, the wall structure (106) is configured such that a diverging portion of the light is partially transmitted through the wall structure (106) and is directed toward the light exit window (104) in part by being specularly reflected by the wall structure.

Description

Technical Field

[0001] The present invention generally relates to lighting devices. Background Art

[0002] Glare is a significant quality aspect of all lighting systems. Therefore, reducing glare to an acceptable level is a common goal. Traditionally, glare reduction has been achieved by using elements such as foils, reflectors, or prismatic sheets to reduce brightness at wide viewing angles relative to the optical axis of the light source (e.g., viewing angles exceeding 60 degrees for indoor lighting and 75 degrees for outdoor lighting). Glare reduction has been associated with changes in light distribution, thereby increasing visual comfort. However, in some applications (both indoor and outdoor), it may be desirable to reduce glare without changing the initial intensity distribution of the light emitted by the light source, for example because the intensity distribution is fixed by the lighting target, or because further glare reduction is required. One approach to achieving this is to increase the light source's luminous area, which automatically results in lower brightness at the same luminous intensity. However, this increased area is associated with disadvantages, such as negative cost and environmental impacts due to increased material usage (optics, fixtures, housing, etc.) and increased bulk and weight during transportation and installation.

[0003] WO2013057644A1 discloses a beam splitting lamp and a lighting system having a transflective outer wall. Summary of the Invention

[0004] An object of the present invention is to provide a lighting device that reduces glare while avoiding or mitigating one or more of the aforementioned disadvantages. More specifically, the object is to reduce glare without physically increasing the light-emitting area of ​​the light source. These and other objects are achieved by a lighting device according to the independent claims. Embodiments of the invention are defined in the dependent claims.

[0005] Therefore, according to one aspect of the present invention, there is provided a lighting device comprising: a light source configured to emit light along an optical axis from a light emitting area of ​​the light source toward a light exit window of the lighting device; and a transflective wall structure for reducing glare of the light-emitting area when viewed through the wall structure, the wall structure surrounding the light-emitting area and extending between the light-emitting area and the light exit window in a direction substantially parallel to the optical axis, wherein the light emitted from the light emitting area comprises a direct portion propagating directly between the light emitting area and the light exit window, and a divergent portion incident on an inwardly facing surface of the wall structure, and The transflective wall structure is transparent and specularly reflective, so that the diverging part of the light is partly transmitted through the wall structure and partly guided to the light exit window by specular reflection from the wall structure.

[0006] The present invention is therefore based on the concept of reducing glare by providing a virtual increase in the light-emitting area of ​​a light source. That is, when the light-emitting area of ​​a light source (hereinafter also referred to as the source area, or the (diffuse) light-emitting area, or the (diffuse) light-emitting surface) is viewed through a transflective wall structure (e.g., a sidewall portion thereof), the divergent portion of the emitted light will be intercepted by the transflective wall structure, and the source area will thereby be obscured. This will reduce the average brightness of the source area as viewed through the transflective wall structure. Simultaneously, the reflected portion of the divergent portion of the light will appear to originate from a virtual source area adjacent to the original source area, having a lower brightness than the original brightness of the physical source area. In this way, a larger combined virtual source area can be created with substantially maintained intensity and lower brightness, as well as a lower glare level. Due to the specular reflectivity of the inward-facing surface of the wall structure, light may undergo multiple specular reflections between inward-facing surface portions before being transmitted through the wall structure or through the light exit window.

[0007] To maximize the benefit of effective glare reduction, the wall structure should generally be positioned as close to the periphery of the source region as possible. There is preferably no separation or gap between the wall structure and the source region, i.e., the luminous region contacts the transflective wall, such that the source and virtual source are connected. This gap creates a "dark" transition region, which can produce undesirable contrast between the source region and the virtual source surface. As can be appreciated, the size of the separation / gap at which this may become noticeable generally depends on the viewing distance.

[0008] The term "transflective" herein means that the wall structure (e.g., any given sidewall portion thereof) is translucent, i.e., both transparent and (specularly) reflective, such that light incident on the inwardly facing surface of any given portion of the wall structure is partially specularly reflected and partially transmitted through that portion. Hereinafter, any reference to "reflection," "reflectivity," or the like should be understood to refer to "specular" reflection or reflectivity, unless otherwise indicated.

[0009] The term "transparent" here means that the transmission of light is non-scattering, in other words, that light is allowed to pass through the wall structure without any significant scattering.

[0010] Typically, the wall structure connects the light emitting area and the light exit window, in that it extends from the light emitting area to the light exit window.

[0011] According to one embodiment, the wall structure has a specular reflectivity of light emitted by the light source in the range of 14% to 86%, preferably 20% to 80%, or even more preferably 40% to 60%. Spectral reflectivity within these ranges has been shown to allow for increasingly effective glare reduction. Generally speaking, the reflectivity should be high enough so that the virtual source region is bright enough to be considered part of the original source region. On the other hand, it should be low enough so that the original source is still bright enough. In particular, the reflectivity range can be a range of average specular reflectivity of the wall structure averaged over a range of incident angles.

[0012] According to one embodiment, the wall structure includes first and second sidewall portions, which are arranged on opposite sides of the optical axis and at the same distance from the optical axis. This arrangement of the opposing sidewall portions allows incident light from the light source to be specularly reflected multiple times between the sidewall portions before being transmitted through the wall structure or through the light exit window. Arranging the first and second sidewall portions at the same distance from the optical axis L provides the same degree of glare reduction when viewing the light-emitting area through either the first or second sidewall portion.

[0013] According to one embodiment, the light source is configured to emit light with a luminous intensity distribution having at least a first plane of symmetry, wherein the first and second sidewall portions are planar sidewall portions substantially parallel to the first plane of symmetry and are arranged on opposite sides of and at the same distance from the first plane of symmetry. Thus, the plane of symmetry of the luminous intensity distribution provided by the physical source region can be maintained by the luminous intensity distribution provided by the virtual source region. The symmetrical placement of the first and second sidewall portions relative to the plane of symmetry ensures that reflections from one sidewall portion in a direction toward the other sidewall portion are offset by reflections from the other sidewall portion in an opposite direction, resulting in an unchanged overall intensity distribution.

[0014] According to one embodiment, the wall structure comprises third and fourth side wall portions connecting the first and second side wall portions and arranged on opposite sides of the optical axis. Thus, the transflective wall structure can form a hollow box, thereby completely surrounding the source region and the optical axis in a circumferential direction.

[0015] According to one embodiment, the luminous intensity distribution further has at least one second symmetry plane transverse to the first symmetry plane, and wherein the third and fourth sidewall portions are flat sidewall portions substantially parallel to the second symmetry plane and are arranged on opposite sides of the second symmetry plane and at the same distance from the second symmetry plane. Thus, the two transverse symmetry planes of the luminous intensity distribution provided by the physical source (i.e., the light beam having quadrant symmetry) can be maintained by the luminous intensity distribution provided by the virtual source region.

[0016] According to one embodiment, the light source is configured to emit light with a luminous intensity distribution that is radially symmetric relative to an optical axis, and the wall structure is radially symmetric relative to the optical axis, or the wall structure includes first, second, third, and fourth flat sidewall portions arranged in a rectangular or square shape centered on the optical axis. This allows for a virtual source region that provides a luminous intensity distribution that maintains the radial symmetry of the luminous intensity distribution provided by the physical source region (i.e., a beam that is rotationally symmetric about the optical axis). Symmetry can be maintained using a wall structure that is cylindrical or rectangular (e.g., having a center that coincides with the optical axis / axis of symmetry) or a hollow box (e.g., a rectangular or square-shaped box). A square or rectangular shape corresponds to an n-sided polygon, where n = 4. More generally, the wall structure can include n sidewall portions arranged in an n-sided polygonal shape centered on the optical axis, where n is an even number equal to or greater than 4 (e.g., n = 6, 8, 10, etc.). This shape of the wall structure also allows maintaining the radial symmetry of the luminous intensity distribution, because the reflection at any one of the n side wall portions of the n-sided polygon in the direction towards the side wall portion directly opposite with respect to the optical axis / symmetry axis is cancelled out by the reflection at the other side wall portion in the opposite direction, so that the overall intensity distribution remains unchanged.

[0017] According to one embodiment, the wall structure extends along at least a portion of the periphery of the light-emitting area. In particular, the wall structure may extend along the entire length of the periphery of the light-emitting area. Thus, glare reduction can be provided for any azimuthal viewing angle (where "azimuthal" refers to viewing angle in a plane transverse to the optical axis).

[0018] According to one embodiment, the light emitting area is a diffuse, flat light emitting surface that extends in a plane transverse to the optical axis and the wall structure. The light source may, for example, comprise one or more light emitting devices (such as one or more LEDs) and a diffuse light emitting surface (or (diffuse) light emitting area), the light source being configured to transmit light through the light emitting area. Typically, LEDs are arranged as bright light emitting pixels in a two-dimensional array, which may cause glare due to their high brightness. The diffuse light emitting area of ​​the LED array spreads the light from the LEDs so that the lighting device has a diffusely luminous non-pixelated light source that presents a light emitting surface of relatively uniform brightness and causes the lighting device to emit a diffuse light beam. As a result, both the real view of the light source and the virtual image of the light source appear diffuse, and glare is therefore reduced.

[0019] According to one embodiment, the luminous surface is a Lambertian emitter, which causes the lighting device to emit light with a Lambertian intensity distribution.The physical source area may thus provide an even more uniform luminous intensity distribution, having the same symmetry as the shape of the luminous surface.

[0020] The diffusely luminous surface is associated with the effect that the luminance is relatively high at large angles, i.e. at least 65 degrees (also referred to as L65), to the normal of the diffusely luminous area / surface. In order to benefit even more from the advantageous effects of the invention, it is preferred that, in operation, the luminance at angles α>= 65 degrees is at least 500 cd / m² for both the reflected light and the light transmitted by the transflective wall. 2 This means that for a transflective wall with a reflectivity R of 50% and a transmittance T of 50%, the brightness of the LED should be at least 1000 cd / m² at α = 65 degrees. 2 For other ratios between R and T of the transflective wall, for example, for R=20% and T=80%, then L65>= 2500 cd / m 2 , and for R=14% and T=86%, then L65>= 3600 cd / m 2 Standard L65>=1000 cd / m 2 (where R = T = 50% and 60*60cm panel) meets the requirements that Lambertian panel emission is >1 klm (thousand lumens), Slimblend panel emission is >2 klm, and PowerBalance or MLO type panel emission is >4 klm.

[0021] According to one embodiment, the separation between the wall structure and the periphery of the light emitting area is at most 100 mm, or at most 50 mm, or at most 20 mm. Separations within these respective ranges can limit the luminance contrast in the virtual source image for the mounting heights of lighting fixtures typically used for large street or road lighting applications, industrial or urban outdoor lighting applications, and indoor lighting applications, respectively. Excessive luminance contrast may otherwise reduce the effectiveness of glare suppression. In industrial and outdoor lighting applications, the distance between the viewer and the light source is often greater than in indoor lighting applications, and therefore a larger separation is acceptable. For domestic indoor lighting applications, an even smaller separation of up to 10 mm may be advantageous, i.e., the wall structure can be arranged to have essentially zero separation from the periphery of the light emitting area.

[0022] According to one embodiment, the height of the wall structure relative to the light emitting area is such that the (entire) light emitting area is obscured by the wall structure when viewed from a viewing angle exceeding a threshold angle relative to the optical axis, wherein the threshold angle is in the range of 40-70 degrees. Thus, glare suppression can be provided for viewing angles suitable for many typical lighting applications.

[0023] According to one embodiment, the height of the wall structure relative to the light-emitting region varies along a circumferential direction relative to the optical axis (e.g., along the periphery of the light-emitting region). The angle relative to the optical axis at which the source region is completely obscured by the wall structure can therefore vary along the circumference of the wall structure (i.e., along the azimuthal viewing direction). This can be useful for elongated source regions, such as non-square rectangular source regions, where, for example, the height of the wall structure (which, as explained above, can include first to fourth flat sidewall portions arranged in a rectangular shape) can be greater at the corner portions of the wall structure than at the center portion of the sidewall portion along the source region.

[0024] According to one embodiment, the wall structure has a (average) specular reflectivity that varies along the optical axis. For example, the reflectivity may decrease gradually and / or continuously along the optical axis from the light source to the light exit window (or vice versa). Thus, the amount of light transmitted through the wall structure can be adjusted along the optical axis, for example, to achieve a more uniform brightness.

[0025] According to one embodiment, the exit window is an aperture or a transparent window. In other words, the wall structure may extend to and surround the light exit aperture (ie the open side) or the transparent window of the lighting device. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] This and other aspects of the present invention will now be described in more detail, with reference to the accompanying drawings showing embodiments of the invention.

[0027] Figure 1 A perspective view schematically shows a lighting device according to an exemplary embodiment of the present invention.

[0028] Figure 2 Shown Figure 1 View of a lighting fixture.

[0029] Figure 3a-3d and Figure 4a-4d Shown are brightness images generated using ray tracing software for the bare source region and the corresponding source region when viewed through a transflective wall structure.

[0030] Figure 5a-5b A lighting device without a transflective wall structure is shown as a comparative example ( Figure 5a ), and also shows a lighting device having a transflective wall structure according to an exemplary embodiment ( Figure 5b ). DETAILED DESCRIPTION

[0031] Figure 1A perspective view of a lighting device 100 is schematically shown. The lighting device 100 includes a light source 102 and a light exit window 104. The light exit window 104 can be an open aperture or a transparent window, such as a clear glass window. The light source 102 is divergent and is therefore configured to emit a divergent light distribution or light beam. The light source 102 is configured to emit light from a light emitting area or source area 102a of the light source 102 in a direction along an optical axis L toward the light exit window 104. The optical axis L, as shown, defines the optical axis of the lighting device 100. As will be discussed further below, the optical axis L can constitute an axis of symmetry for the (divergent) light distribution emitted from the light emitting area 102a.

[0032] In the example shown, the source region 102a is a diffuse, flat emitting surface or source surface 102a, which extends in a plane substantially transverse to the optical axis L. The source region 102a is also substantially parallel to the extension plane of the light exit window 104. The light source 102 may, for example, comprise one or more light emitting devices (such as one or more LEDs) which are arranged behind the source surface 102a of the light source and are configured to transmit light through the source surface 102a. The emitting region 102a as shown may be rectangular in shape. However, other shapes are also possible, such as square, annular or circular (e.g. elliptical), for example Figure 5b As shown in .

[0033] Source surface 102a can be a Lambertian emitter. A Lambertian emitter can be implemented using a translucent diffuser screen, where light emitted by the light-emitting device(s) of light source 102 can be transmitted and diffusely scattered by the diffuser screen. In another example, a Lambertian emitter can be implemented using another diffusing optical element, such as a diffusing lens, where source surface 102a can be the exit surface of the diffusing optical element. However, lighting device 100 is not limited to use with a Lambertian light source, but can more generally be used with any light source that provides a divergent light distribution. For example, light source 102 can include various light-shaping optics, such as lenses and / or reflectors, for shaping the light emitted by the light-emitting device(s) into a desired divergent light distribution. In this case, light-emitting area 102a can be an open aperture or a transparent window, such as a clear glass window.

[0034] Still refer to Figure 1The lighting device 100 further includes a transflective wall structure 106, which is a "transflector" or semi-transparent reflector. The light emitted from the light-emitting area 102a includes a direct portion that propagates directly between the source surface 102a and the light exit window 104, and a divergent portion that is incident on the inward-facing surface (106') of the wall structure 106. When viewed through the wall structure 106, the wall structure 106 allows for the reduction or suppression of glare on the light-emitting area 102a caused by the divergent portion of the light. To this end, the wall structure 106 surrounds the light-emitting area 102a without gaps and extends toward the light exit window 104 in a direction substantially parallel to the optical axis L, and thus substantially transversely to the plane of the source surface 102a. In the illustrated example, the wall structure 106 may more specifically extend between the light-emitting area 102a and the light exit window 104, i.e., here, from the light-emitting area 102a to the light exit window 104, thereby connecting the light-emitting area 102a to the light exit window 104.

[0035] More specifically, the wall structure 106 as shown includes first, second, third, and fourth flat sidewall portions 106a-d arranged in the shape of a hollow rectangular box. In the example shown, the "box" or wall structure 106 has an open entrance side facing the source region 102a and an open exit side facing or defining the light exit window 104. The wall structure 106 has a first width dimension A, a second width dimension B, and a height dimension H, wherein the height dimension is defined by the height of the wall structure 106 above the source region 102a, as seen along the optical axis L.

[0036] The first and second sidewall portions 106a-b are substantially parallel to each other and extend along the periphery 102b of the source surface 102a on opposite sides of the optical axis L. In particular, the first and second sidewall portions 106a-b are arranged directly opposite each other so that the inward-facing surface portions of the first and second sidewall portions 106a-b face each other. The first and second sidewall portions 106a-b are connected by third and fourth sidewall portions 106c-d that extend transversely to the first and second sidewall portions 106a-b. The third and fourth sidewall portions 106c-d are substantially parallel to each other and extend along the periphery 102b of the source surface 102a on opposite sides of the optical axis L. In particular, the third and fourth sidewall portions 106c-d are arranged directly opposite each other so that the inward-facing surface portions of the third and fourth sidewall portions 106a-b face each other.

[0037] The first and second side wall portions 106a-b are arranged at the same distance (e.g., A / 2) from the optical axis L. Correspondingly, the third and fourth side wall portions 106c-d are arranged at the same distance (e.g., B / 2) from the optical axis L. Thus, the wall structure 106 can be centered about the optical axis L, i.e., aligned with the optical axis L.

[0038] The wall structure 106 is transflective in the sense that it is transparent and specularly reflective. Thus, a divergent portion of light incident on or intercepted by the inward-facing surface of the wall structure 106 is partially transmitted through the wall structure 106 and partially directed toward the light exit window 104 by specularly reflecting off the wall structure 106 (e.g., off its inward-facing surface). As can be appreciated, the divergent portion of light may be specularly reflected multiple times by the wall structure 106 before being transmitted from the light exit window 104 and, therefore, gradually leaks out due to the transparency of the wall structure and is therefore emitted from the sidewall portions 106a-d of the wall structure 106. For a viewer viewing the source region 102a through a given side wall portion of the wall structure 106, such as the first side wall portion 106a, the light emitted from the first side wall portion 106a will appear to originate from a virtual source region adjacent to the source region 102a, having a lower luminance than the luminance of the physical source region 102a, thereby creating the impression of an enlarged combined virtual source surface having (at least substantially) the same luminous intensity as the physical source surface 102a, but with a lower luminance and a lower glare level.

[0039] exist Figure 1 The angle β in φ indicates the maximum angle relative to the source surface 102a at which the wall structure 106 completely blocks the source surface 102a from any azimuthal viewing direction or angle φ. Figure 1 As can be seen, angle β is defined in a vertical plane, while azimuth angle ϕ is defined in a horizontal plane. "Vertical" and "horizontal" are used here in relative terms only, referring to a plane transverse to the plane of source region 102a and a plane parallel to or coincident with the plane of source region 102a, respectively. As shown, azimuth angle ϕ is more specifically defined relative to a reference axis that coincides with the plane of source region 102a and has its origin at the intersection between optical axis L and source region 102a. In other words, azimuth angle ϕ is the angle between the projection of the viewer's line of sight from the center of source region 102a onto the plane of source region 102a and the reference axis in the plane of source region 102a. As can be appreciated, the reference axis and azimuth angle ϕ can equally well be defined in any (horizontal) plane parallel to source region 102a. At vertical viewing angles greater than angle β, wall structure 106 may only obstruct a portion of source region 102a, thereby still reducing glare, but to a lesser extent. The term "vertical viewing angle" should be understood here as the angle between the optical axis L and the line of sight from the center of the source region 102a to the viewer (e.g. Figure 2 The height H of the wall structure 106 relative to the source region 102a can be such that β is in the range of 20-50°. This is equivalent to the height of the wall structure 106 being such that when the angle α relative to the optical axis exceeds the threshold value, thWhen viewing the source region 102a from a viewing angle of α, the entire source region 102a is blocked by the wall structure 106, where α th In the range from 40-70°, such as α th = 60°.

[0040] The specular reflectivity of the wall structure 106 can be independent of the angle of incidence, allowing the wall structure 106 to exhibit a constant or uniform specular reflectivity. The specular reflectivity of the wall structure 106 can be uniform along the height dimension. However, the reflectivity can also be modulated along the height dimension H, such that the reflectivity of the wall structure 106 depends on the position or height along the height dimension H. This allows the amount of light transmitted through the wall structure 106 to be adjusted along the optical axis L, for example to achieve more uniform brightness. In any case, the wall structure 106 can have a specular reflectivity within a range from 14% to 86%, more preferably 20% to 80%, or even more preferably 40% to 60%, for light emitted by the light source 102. These reflectivity ranges enable increasingly effective glare reduction. Depending on the composition and material of the wall structure 106, the reflectivity may exhibit a dependence on the angle of incidence of the light. Therefore, the specular reflectivity may refer to the average specular reflectivity of the wall structure, where the average represents the angular average, i.e., the specular reflectivity averaged over a range of incident angles, such as 0° to 90°. However, the average specular reflectivity may also be determined within a narrower range of incident angles corresponding to a range of relevant vertical viewing angles at which glare reduction is to be provided, such as within a range of incident angles from 0° to 50°.

[0041] The transflective wall structure 106 can be adapted to exhibit no or substantially no significant absorption in the wavelength region of interest (e.g., the visible portion of the spectrum emitted by the light source 102). In practice, for the contemplated compositions and structures of the wall structure 106, an absorptivity of less than 5%, or even less than 1%, can be readily achieved. Thus, the absorptivity A of the transflective wall structure 106 can be considered to be a good approximation of zero, where the transmittance T and the specular reflectance R (e.g., averaged over the wall structure 106 or at a given location) can be related by R=1-T.

[0042] Transflective wall structures can be implemented in a variety of ways. Wall structure 106 can be formed from glass, quartz, or a polymer such as polycarbonate or poly(methyl methacrylate) (PMMA), coated with multiple layers of dielectric. The multiple layers can be optimized to achieve the desired reflectivity. The coating can be applied to either the inward-facing surface of wall structure 106 or the outward-facing surface. According to other examples, the reflectivity can be determined by a silver or aluminum layer (with a thickness adjusted to provide the desired transmittance). According to yet another example, wall structure 106 can be formed from a stack of thin transparent layers (such as two to three or more transparent layers of glass, quartz, or polymer film or foil), with air gaps (>1 μm) between them. In this case, the reflectivity of wall structure 106 can be adjusted by the number of thin layers and the refractive index of the transparent layers. For example, using two layers of PMMA, a vertical reflectivity of approximately 14% (at a 90° angle of incidence) can be achieved, increasing to approximately 19% at a 50° angle of incidence. Three layers of PMMA provide a vertical reflectivity of approximately 20%.

[0043] For effective glare reduction, the wall structure 106 should generally be positioned as close as possible to the periphery 102b of the source area 102a. The separation or gap between the wall structure and the source area 102a creates a "dark" transition zone, which can produce undesirable contrast between the source area 102a and the virtual source surface. As can be appreciated, the separation at which this may become apparent typically depends on the viewing distance. In practice, a separation of up to 100 mm between the wall structure 106 and the periphery 102b of the light emitting area 102a may be suitable for larger street and road (e.g., highway) lighting applications, or up to 50 mm for industrial lighting applications or urban and smaller street lighting applications, or up to 20 mm for indoor workplace lighting applications (e.g., offices, corridors, hotels), or up to 10 mm for indoor home lighting applications, or even substantially / effectively zero.

[0044] In the case where source region 102a is a Lambertian source surface, due to the rectangular shape of source surface 102a as shown, light will be emitted from source surface 102a with a luminous intensity distribution having a first symmetry plane and a second symmetry plane transverse to the first symmetry plane (which intersect each other along optical axis L). In this case, the first and second sidewall portions 106a-b will be substantially parallel to the first symmetry plane and located on opposite sides of the first symmetry plane. Correspondingly, the third and fourth sidewall portions 106a-b will be substantially parallel to the second symmetry plane and located on opposite sides of the second symmetry plane. As a result, wall structure 106 maintains the first and second symmetry planes of the luminous intensity distribution of the physical source surface 102a.

[0045] In an ideal situation (e.g., a true Lambertian source surface 102a, sidewall portions 106a-b, and 106c-d perfectly parallel to their respective symmetry planes, and exhibiting zero absorption), transflective wall structure 106 would theoretically produce a virtual source image at every location on wall structure 106 and from every relevant viewing direction. In this case, the entire source surface 102a plus the surface of transflective wall structure 106 would be perceived as a glare source. Thus, when viewed through wall structure 106, the glare source (i.e., source region 102a) would no longer be perceived as a flat, rectangular source with sides A and B (assuming wall structure 106 is arranged with zero separation from periphery 102b of source surface 102a), but rather as a block-shaped, volumetric source with sides A and B (in mm) and a height H.

[0046] As an illustrative and non-limiting example, assume a square Lambertian source surface 102a with A = B = 100 mm and a luminous flux of 1000 lm. This is a very bright and glaring light source, with a UGR (Uniform Glare Rating) of 30 (according to the UGR table method, in a standard space with standard dimensions, surface reflectivity, luminaire spacing, and observer position defined by the Commission Internationale de l'Eclairage (CEN)). Luminaires with such high UGR values ​​are generally considered very uncomfortable and even border on causing unbearable glare. Choosing an angle β = 45°, which corresponds to a height H = 142 mm, and a reflectivity of 50%, results in an ideal UGR value of 24. This is still glaring in some situations (such as office lighting), but is comfortable enough for circulation areas, corridors, or industrial activities. This improvement of 6 UGR points (2 UGR levels) is a significant improvement in glare performance. However, in practice, the virtual source image pattern will typically not produce a uniform luminous pattern that illuminates the entire surface of the wall structure 106 from all relevant viewing directions. Therefore, the improvement in glare performance will generally be less in practice than in the ideal case.

[0047] Improved estimates of glare performance for realistic luminance patterns can be obtained using ray-tracing software and by evaluating glare performance using a generic glare model that makes no assumptions about the source area (unlike the UGR). Below, glare perception scores (GSS) are calculated for a wide range of viewing angles α and transflective wall reflectance values. It is important to note that the GSS method considers only a single observer and a single glare source, unlike the UGR tabular method, which evaluates glare for a grid of luminaires on the ceiling of an interior space. Therefore, these GSS results are not directly comparable to UGR values, as they may be different for other viewing distances or angles.

[0048] The calculation of GSS requires several input parameters, as described by Vissenberg et al. (A generic, visual system-based model for discomfort from glare. Lighting Research&Technology. July 2022. doi:10.1177 / 14771535221112675). The main parameters used for the calculation are: - High-resolution brightness images from source and transflective wall structures.

[0049] - The vertical viewing angle α and the viewing distance d, which define the distance between the viewer and the light source.

[0050] - Adaptive or background illumination.

[0051] - Eye illuminance, as determined by the source intensity (taking into account transflective wall structures) and the angle of incidence on the eye.

[0052] Combine Figure 2 The following discussion can be better understood, Figure 2 A schematic side view of the lighting device 100 and the definitions of α and d are shown. Figure 2 In the selected view, Figure 2 The angle β shown in corresponds to the projection of β onto the viewing plane, and the correct definition of β is Figure 1 In this figure, the lighting device 100 is shown by way of example, wherein the optical axis L and the light exit window 104 are oriented in a top-down direction, for example representing a downlight luminaire. However, this is only an example, and other orientations and use cases are equally possible.

[0053] GSS is determined for two viewing conditions: foveal and peripheral. Figure 2 Scenario "F" in the figure means that the viewer is looking directly at the light source, which is obviously the worst-case viewing condition for direct glare. Figure 2 The scenario "P" in ) means that the viewer is looking towards the horizon or "straight ahead" (this is the viewing direction assumed in UGR calculations).

[0054] Figure 3a-3d and Figure 4a-4d The luminance images of the bare source surface 102a (ie, without the transflective wall structure 106) and the source surface 102a viewed through the transflective wall structure 106 are shown, with a viewing angle of α = 45° ( Figure 3a and Figure 4a )、α= 55°( Figure 3b and Figure 4b ),α= 65°( Figure 3cand Figure 4c ) and α = 75° ( Figure 3d and Figure 4d ), which are calculated in a ray tracing software (LightTools 9.1 from Synopsis). The source surface 102a is in each case a square Lambertian surface with A = B = 100 mm and a luminous flux of 1000 lm. Figure 3a-3d and Figure 4a-4d In each of the images, the graphs to the right and below the luminance image respectively show the luminance along Y=0 and X=0 in the luminance image. Assume that the reflectivity of the wall structure 106 is 50%.

[0055] Calculate the foveal visual field (E) using equations (1)-(4) foveal ) and peripheral vision (E peripheral ) for both eye illumination from the source: (Equation 1) (Equation 2) (Equation 3) (Equation 4) Where Flux is the luminous flux [lm], I α is the luminous intensity [cd] at viewing angle / emission angle α, and d = 2 [m]. The eye illuminance also includes the light from the room background (150 lux). Table I presents the eye illuminance values ​​[lm / m 2 ] calculation results. Viewing angle α[degrees] Eye illuminance [lux] (foveal visual field) Eye illuminance [lux] (peripheral vision) 45 56.25 39.75 55 45.63 37.38 65 33.63 30.50 75 20.63 19.94 Table I.

[0056] From Figure 4a-4d It can be seen from the brightness image in that the surface of the wall structure 106 is not uniformly illuminated, and at some viewing angles, parts of the transflective wall remain relatively dark, which may result in less glare suppression. Figure 3a-3d The brightness image in Figure 4a-4d From the brightness image in FIG, it can be further observed that the wall structure 106 reduces the peak brightness and increases the luminous area of ​​the source. The peak brightness is independent of the viewing angle.

[0057] Table II and Table III show the results of the experiment for the assuming that the adaptation brightness is 150 lux. Figure 3a-3d and Figure 4a-4d GSS values ​​calculated for all images in . α Walled GSS (fovea) GSS without wall structure (fovea) ΔGSS = GSS (with wall structure) – GSS (without wall structure) 45 2.34 2.44 -0.10 55 2.20 2.32 -0.12 65 2.01 2.16 -0.15 75 1.79 1.94 -0.15 Table II α GSS with wall structure (peripheral) GSS without wall structure (peripheral) ΔGSS = GSS (with wall structure) – GSS (without wall structure) 45 1.15 1.26 -0.11 55 1.22 1.40 -0.18 65 1.42 1.67 -0.25 75 1.52 1.81 -0.29 Table III.

[0058] Tables II and III show that for two viewing conditions (foveal and peripheral), the transflective wall structure 106 provides a reduction in GSS values. For peripheral viewing, the reduction in GSS values ​​is greatest.

[0059] Based on Vissenberg et al., it can be inferred that the glare reduction in the foveal visual field (approximately 0.13 GSS) is equivalent to approximately 1.5 UGR points, and the glare reduction in the peripheral visual field (approximately 0.21 GSS) is equivalent to approximately 2.5 UGR points, or almost one UGR grade. This is less than the idealized improvement of 6 UGR points, which may be due in part to the specific observer-source distance (glare reduction may be greater at other distances) and in part to the uneven luminance pattern. In the peripheral visual field, people are much less sensitive to luminance patterns, which explains why glare reduction is more effective in the peripheral field than in the foveal field.

[0060] Figure 5a-5b A luminaire including a lighting device without a transflective wall structure according to an exemplary embodiment is provided. Figure 5a ) and a luminaire including a lighting device having a transflective wall structure ( Figure 5b By way of example, the luminaire is shown in the form of a downlight mounted on a ceiling. Figure 5a The upper part of shows a ray traced image of an unobstructed light source 202 of a luminaire (which corresponds, for example, to a conventional arrangement of downlights). In this example, the light source 202 comprises a circular source area (or surface) 202a. Figure 5a The lower portion is a schematic depiction of a cross section taken along a diameter of source region 202a, and an eye viewing through the fovea of ​​source region 202a.

[0061] Figure 5b The upper and lower parts of the luminaire show corresponding views when the lighting device 200 of the luminaire is provided with a transflective wall structure 206, which is more specifically a cylindrical wall structure surrounding the circular source area 202a and is parallel to the optical axis L and symmetrical about the optical axis L. As taken through the mutually opposite (curved) side wall portions 206a-b of the wall structure 206 Figure 5b As shown in the cross-sectional view in the lower portion, specular reflection and non-scattered transmission of the wall structure 106 result in a virtual image 202b of the physical source region 202a. As further shown, a portion 202ab of the physical source region 202a is visible through the side wall portion 206a, so that the observer directly views only a portion 202aa of the source region 202a. Thus, the combined source image as seen by the observer is formed by the union of 202aa, 202ab, and 202b, thereby being identical to the virtual image 202b of the physical source region 202a. Figure 5a Provides reduced glare compared to a naked view of the source area 202a.

[0062] Those skilled in the art realize 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. For example, Figure 1 In the illustrated example of FIG, the first, second, third, and fourth planar sidewall portions 106a-d extend along the entire length of the periphery 102b of the source surface 102a. In other words, the wall structure 106 completely surrounds the source region 102a and the optical axis L in a circumferential direction. While this may be advantageous in that glare reduction can be provided for any azimuthal viewing angle φ, a full circumferential extension is not required in all applications. For example, in some lighting applications, it may be sufficient to reduce glare from two opposing sides of the source region 102a, such as for a light source that provides a luminous intensity distribution having only a single plane of symmetry (one example is road lighting). Reference Figure 1 , a modified wall structure for such an application may be formed of, for example, only the first and second side wall portions 106a-b, parallel to and on opposite sides of a single symmetry plane, and having open sides, instead of the third and fourth side wall portions 106c-d. Additionally, in the case where the light source emits light with a luminous intensity distribution that is radially symmetric with respect to the optical axis L, as Figure 5b In the embodiment, a rectangular or square box-shaped wall structure centered on the optical axis L can be used instead of the cylindrical wall structure 206. More generally, the wall structure can include a number n of side wall portions arranged in an n-sided polygonal shape centered on the optical axis (L), where n is an even number equal to or greater than 4. The case of n = 4 corresponds to the aforementioned rectangular or square shaped arrangement of the side wall portions 106a-d. However, a larger number of side wall portions (e.g., n = 6 corresponds to a hexagon, n = 8 corresponds to an octagon, n = 10 corresponds to a decagon, etc.) is also possible. A polygon with an even number n of sides (e.g., 4, 6, 8, 10, ...) enables the wall structure to be arranged so that each of the n side wall portions has a corresponding parallel side wall portion on directly opposite sides of the optical axis L. The polygon can, for example, be a regular n-sided polygon (such as a square, a regular hexagon, a regular octagon, etc.). According to another example, the height H of the wall structure 106 can vary along the circumferential direction (which corresponds to the azimuthal viewing angle φ). For example, if A>B (which means Figure 1 d), the first and second sidewall portions 106a-b may have a greater height H than the third and fourth sidewall portions 106c-d to shield the source region 102a such that a vertical minimum or threshold viewing angle α (i.e., α th) is the same, above which the source region 102a is completely obscured by the wall structure 106. The height may also be varied continuously along the circumference to obtain a minimum vertical viewing angle α (α th ), above this minimum vertical viewing angle α, the source region 102a is completely obscured by a wall structure that varies depending on the azimuthal viewing angle φ or is constant (e.g., a rectangular wall structure with increasing height at the corners). Furthermore, while example embodiments of the lighting device 100 have been disclosed above with reference to a flat light emitting region or surface 102a, it should be noted that the concepts are also applicable to non-planar geometries, such as light sources including curved (e.g., circular or bulb-shaped) source surfaces.

Claims

1. A lighting device (100), comprising: A light source (102) comprising one or more light emitting devices (LEDs) and a diffuse light emitting area (102a), the light source being configured to transmit light along an optical axis (L) through the light emitting area (102a) towards a light exit window (104) of the lighting device (100), the light emitting area having a periphery (102b); and a transflective wall structure (106) for reducing glare of the light emitting area (102a) when viewed through the wall structure (106), the wall structure (106) surrounding the light emitting area (102a) and extending between the light emitting area (102a) and the light exit window (104) in a direction substantially parallel to the optical axis (L), wherein the light emitted from the light emitting area (102a) includes a direct portion propagating directly between the light emitting area (102a) and the light exit window (104), and a divergent portion incident on the inwardly facing surface (106') of the wall structure (106), and The transflective wall structure (106) is transparent and specularly reflective, so that the divergent part of the light is partially transmitted through the wall structure (106) and is partially guided to the light exit window (104) by being specularly reflected by the wall structure (106).

2. The lighting device (100) according to claim 1, wherein the wall structure has a specular reflectivity in the range from 14% to 86%, preferably 20% to 80%, or even more preferably 40% to 60% for light emitted by the light source (102).

3. The lighting device (100) according to any one of claims 1-2, wherein the wall structure (106) comprises a first and a second side wall portion (106a-b; 206a-b), the first and the second side wall portion (106a-b; 206a-b) being arranged on opposite sides of the optical axis (L) and at the same distance from the optical axis (L).

4. The lighting device (100) of claim 3, wherein the light source (102) is configured to emit light with a luminous intensity distribution having at least a first plane of symmetry, and wherein the first and second side wall portions (106a-b) are flat side wall portions that are substantially parallel to the first plane of symmetry and are arranged on opposite sides of the first plane of symmetry and at the same distance from the first plane of symmetry.

5. The lighting device (100) according to claim 4, wherein the wall structure (106) comprises third and fourth side wall portions (106c-d) connecting the first and second side wall portions (106a-b) and arranged on opposite sides of the optical axis (L).

6. The lighting device (100) according to claim 5, wherein the luminous intensity distribution further has at least one second symmetry plane transverse to the first symmetry plane, and wherein the third and fourth side wall portions (106c-d) are flat side wall portions substantially parallel to the second symmetry plane and are arranged on opposite sides of the second symmetry plane and at the same distance from the second symmetry plane.

7. The lighting device (100) according to any one of claims 1 to 3, wherein the light source (102) is configured to emit light with a luminous intensity distribution that is radially symmetric with respect to the optical axis (L), and wherein the wall structure (106) is radially symmetric with respect to the optical axis (L), or wherein the wall structure (106) includes n side wall portions (106a-d) arranged in the shape of an n-sided polygon centered on the optical axis (L), wherein n is an even number equal to or greater than 4.

8. The lighting device (100) according to any one of the preceding claims, wherein the wall structure (106; 206) extends along at least a portion of a periphery (102b) of the light emitting area (102a).

9. The lighting device (100) according to claim 8, wherein the wall structure (106; 206) extends along the entire length of the periphery (102b) of the light emitting area (102a).

10. The lighting device (100) according to any of the preceding claims, wherein the light emitting area is a flat light emitting surface (102a) extending in a plane transverse to the optical axis (L) and the wall structure (106; 206), the wall structure being arranged with substantially zero separation from a periphery (102b) of the light emitting area (102a).

11. The lighting device (100) according to claim 10, wherein the light emitting surface (102a) is a Lambertian emitter.

12. The lighting device (100) according to any one of the preceding claims, wherein the height of the wall structure (106) relative to the light emitting area (102a) is such that the light emitting area (102a) is obscured by the wall structure (106) when viewed from a viewing angle exceeding a threshold angle relative to the optical axis (L), wherein the threshold angle is in the range from 40-70°.

13. The lighting device (100) according to any one of the preceding claims, wherein a height of the wall structure (106) relative to the light emitting area (102a) varies along a circumferential direction relative to the optical axis (L).

14. The lighting device (100) according to any one of the preceding claims, wherein the wall structure has a specular reflectivity that varies along the optical axis (L).

15. The lighting device (100) according to any one of the preceding claims, wherein in operation the diffuse luminous area (102a) has a brightness of at least 1000 cd / m2 at an angle α >= 65 degrees to the normal of the diffuse luminous area (102a). 2 brightness.

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