A lens plate for use in a luminaire

Abstract

The invention relates to a lens plate (300) comprising a plurality of lens elements (310) on a substrate (320). Each lens element (310) has an optical axis (330) oriented perpendicular to the substrate (320). Each lens element (310) further has a lower part (311) and an upper part (312), the lower part (311) being adjacent to the substrate (320). The lower part (311) has an outer surface extending around the optical axis (330) and being provided with a surface texture, while the upper part (312) is transparent. Each lens element (310) has a first height, and each upper part (312) has a second height. A height ratio of the second height and the first height is at least 0,1 but not more than 0,7. Compared to a lens plate with lens elements that are fully clear, the lens plate (300) according to the invention has no significant influence on the light distribution, but it is arranged to provide an improved color homogeneity.

Description

[0001]2024PF80248 1A LENS PLATE FOR USE IN A LUMINAIRE FIELD OF THE INVENTION The invention relates to a lens plate that can be used in a luminaire. The invention further relates to a luminaire that comprises the lens plate. BACKGROUND OF THE INVENTION Luminaires may be used to provide comfortable workplace illumination in avariety of environments, such as an office environment, a retail environment, an educationalenvironment, or an industrial environment.Several factors play a role in achieving comfortable workplace illumination.One of these factors is glare, or the difficulty of seeing in the presence of bright light. Theperformance of a luminaire in terms of glare can be characterized by various indicators. A first performance indicator is the Unified Glare Rating (UGR). This a measure of the glare in a given environment, adopted by the International Commission on Illumination (CIE). A second performance indicator is the luminance as a function of angle relative to the normal. Luminance is a measure of the luminous intensity per unit area of light, and unlike UGR, it is a function of the luminaire itself, and it is not affected by the properties of the environment wherein the luminaire is installed. For comfortable workplace illumination, the UGR and the luminance at angleshigher than 65 degrees from the normal should typically be limited to a certain thresholdvalue, which threshold may depend on the environment that is to be illuminated. The above requirements can be met by using a lens plate to shape the lightbeams emitted by the light engine of the luminaire. Besides glare, other factors also play a role in achieving comfortable workplace illumination. One of these other factors is the homogeneity of the light distribution. Inhomogeneity issues may be the result of undesired color-over-angle effects, which may particularly occur when light emitting diodes (LEDs) are used in the light engine.2024PF80248 2The most common method of providing white light from an LED is to converta primary light output by means of a photoluminescent material. Primary light rays that are emitted at relatively large angles with respect to the normal have a longer optical path through the photoluminescent material than primary light rays that are emitted at a smaller angle. The longer the optical path through the photoluminescent material, the more absorption of the primary light. Consequently, light that is emitted from a (phosphor-converted) LED at relatively high angles may have less primary light and more converted light, resulting in a variation of color over angle, and hence inhomogeneities in the light distribution. Inhomogeneities in the light distribution, such as color-over-angle effects, maybe removed from a light beam by using a light diffusing optical component. However, diffusion of light generally makes it difficult to still meet requirements as to glare. SUMMARY OF THE INVENTION It is an object of the invention to provide a luminaire that performs well in terms of glare (in particular, that it can meet desired UGR and luminance requirements) while at the same time it performs well in terms of homogeneity of the light distribution (in particular, that it does not suffer from color-over-angle effects). In a first aspect of the invention, the object is achieved by a lens plate that can be used in a luminaire. The lens plate comprises a plurality of lens elements on a substrate. Each lens element has an optical axis oriented perpendicular to the substrate. Each lens element further has a lower part and an upper part, the lower part being adjacent to the substrate. The lower part has an outer surface extending around theoptical axis and being provided with a surface texture, while the upper part is transparent.Each lens element has a first height, and each upper part has a second height,the first height and the second height being measured along the optical axis. A height ratio ofthe second height and the first height is at least 0,1 but not more than 0,7. Compared to a lens plate with lens elements that are fully clear (i.e., transparent and free of any surface texture), the lens plate according to the first aspect has no significant influence on the light distribution, but it is arranged to provide an improved color homogeneity.2024PF80248 3In the lens plate, the height ratio of the second height and the first height maybe at least 0,3 but not more than 0,6. Hereby, the color homogeneity is even further improved,while there is still no significant influence on the light distribution. In the lens plate, the upper part may be a spherical cap, and the lower part a spherical segment. The spherical segment then has a first base radius at a first side facing thesubstrate, and a second base radius at a second side facing away from the substrate. A baseratio of the second base radius and the first base radius is then at least 0,5, or even at least 0,7. A lens plate with such a configuration provides the desired improvement in color homogeneity, while it can be easily manufactured, and allows the advantages to be provided for an extended range of applications. In the lens plate, the surface texture may have an arithmetic average roughnessin a range of 0,3 to 3 micrometers, such as in a range of 0,4 to 2 micrometers. Lens elementswith such surface textures can be easily manufactured, and they provide the desired improvement in color uniformity while not significantly influencing the light distribution. In a second aspect of the invention, the object is achieved by a luminaire that comprises the lens plate according to the first aspect. The luminaire further comprises a plurality of light emitting elements, each light emitting element being positioned on the optical axis of an associated lens element of the lens plate. The luminaire may further comprise a light diffusing cover plate provided over the lens plate. In the luminaire, the light emitting elements may be light emitting diodes. BRIEF DESCRIPTION OF THE DRAWINGS Embodiments of the invention will now be described, by way of example only, with reference to the accompanying schematic drawings in which corresponding reference symbols indicate corresponding parts. Fig.1 shows an exploded view of a luminaire. Fig.2 shows a lens plate. Fig. 3 shows a lens plate according to the invention.Fig. 4 shows a close-up of a lens elements of the lens plate of Figure 3.Fig. 5 shows a hemisphere for illustrating various parameters of a lenselement. Fig. 6 shows a graph of the base ratio a function of the height ratio.Fig. 7 shows an exploded view of a luminaire according to the invention.2024PF80248 4Fig. 8 shows two photographs of different luminaires.Fig. 9 shows two polar luminous intensity diagrams.Fig. 10 shows two plots of color point data.The schematic drawings are not necessarily to scale. DETAILED DESCRIPTION OF THE EMBODIMENTS Figure 1 shows an exploded view of a luminaire 1000. The luminaire 1000 comprises a lens plate 100, arranged between a lightengine 400 and a light diffusing cover 500. The luminaire 1000 may further comprise othercomponents, such as a housing and a driver, but for the sake of clarity such further components are not shown in Figure 1. The lens plate 100 has a plurality of lens elements 110 on a substrate 120. Thesubstrate 120 has an upper substrate surface 121 and an opposite lower substrate surface 122.The lens elements 110 are provided on the upper substrate surface 121.Each lens element 110 has a convex outer surface and is hence arranged tonarrow the angular distribution of a light beam by means of refraction. In the lens plate 100,the lens elements 110 are all transparent (or clear).The light engine 400 comprises a plurality of light emitting elements 410 on acarrier 420. The light emitting elements 410 may be light emitting diodes (LEDs), or anyother suitable light emitting element, and the carrier 420 may be a printed circuit board(PCB), or any other suitable carrier. The light engine 400 faces the lower substrate surface 122 of the lens plate100, and the light emitting elements 410 are arranged to emit light towards the lens plate 100.Each lens element 110 of the lens plate 100 has an optical axis 130. Theoptical axis 130 is an imaginary straight line that is oriented perpendicular to the substrate120 and that passes through the geometrical center of the associated lens element 110.Each light emitting element 410 of the light engine 400 is positioned on theoptical axis 130 of an associated lens element 110 of the lens plate 100.The light diffusing cover 500 is provided over the lens plate 100. In otherwords, the upper substrate surface 121 (and the lens elements 110) face the light diffusingcover 500. When the luminaire 1000 is in operation, each light emitting element 410 ofthe light engine 400 emits a light beam with a certain angular distribution. This light beam isthen incident on a lens element 110 of the lens plate 100. Upon passing the lens element 110,2024PF80248 5the angular distribution of the emitted light beam is narrowed. The narrowed light beam then passes through the light diffusing cover 500, as a result of which the angular distribution is widened again. The light diffusing cover 500 is arranged to provide a relatively homogeneous light emitting surface, and to prevent the light emitting elements 410 from appearing as bright dots. Furthermore, the light diffusing cover 500 may help to hide constructional elements such as screws. The luminaire 1000 is capable of providing a comfortable workplace illumination. Comfortable workplace illumination is provided when a correct level oflighting is achieved to ensure that people have a clear visibility. Various factors play a role in achieving comfortable workplace illumination, one of which is glare, or the difficulty of seeing in the presence of bright light. Glare from luminaires can be expressed with the so-called Unified Glare Rating (UGR). This a measure of the glare in a given environment, adopted by the International Commission on Illumination (CIE). To ensure a comfortable workplace illumination in an office environment, aretail environment, or an educational environment, the UGR preferably has a value lower than 22. For comfortable workplace illumination in an industrial environment, the UGR may be somewhat higher, but it preferably has a value lower than 25. Besides UGR, another important performance indicator of a luminaire is the luminance as a function of angle relative to the normal. Luminance is a measure of theluminous intensity per unit area of light, and unlike UGR, it is a function of the luminaireitself, and it is not affected by the properties of the environment wherein the luminaire is installed. In addition to limiting the UGR, it is typically also preferred that a luminaire has a maximum luminance at angles higher than 65 degrees from the normal. This may be referred to as the L65 requirement. For example, for use in an office environment, a luminairepreferably has a luminance of less than 3,000 candela per square meter at angles higher than65 degrees from the normal. The combination of the lens plate 100 and the light diffusing cover 500 allows the luminaire 1000 to meet the desired UGR and L65 requirements. However, the luminaire 1000 still has a drawback in that the light diffusingcover plate 500 may not be homogeneously illuminated.2024PF80248 6This drawback may particularly occur when the light emitting elements 210 are LEDs wherein a primary light output is converted by means of a photoluminescent material, as is the case for the most common method of providing white light from an LED. Primary light rays that are emitted at relatively large angles with respect to the normal have a longer optical path through the photoluminescent material than primary light rays that are emitted at a smaller angle. The longer the optical path through the photoluminescent material, the more absorption of the primary light. Consequently, light that is emitted from a (phosphor-converted) LED at relatively high angles will typically have less primary light and more converted light, resulting in a variation of color over angle. Undesired color-over-angle effects may be removed from a light beam by letting the latter pass through a light diffusing component. However, this would negate the aforementioned advantages in terms of glare. For example, instead of the lens plate 100 one may use lens plate 200 shown in Figure 2. Similar to lens plate 100 shown in Figure 1, lens plate 200 has a substrate 220 with an upper substrate surface 221 and an opposite lower substrate surface 222, wherein aplurality of lens elements 210 is provided on the upper substrate surface 221.Where the lens elements 110 of the lens plate 100 are transparent (or clear), thelens elements 210 of the lens plate 200 all have a fully textured outer surface. In other words,the outer surfaces of the lens elements 210 have a certain surface roughness, which will resultin light rays being scattered to a certain degree upon passing through the lens elements 210.The lens elements 210 may help to at least reduce any color-over-anglevariation of light beams emitted by a light engine. However, it will be difficult to meet UGR and L65 requirements, and one may even need to include additional, and potentially expensive, optical components in the luminaire. Figure 3 shows lens plate 300, being a lens plate according to the present invention. The lens plate 300 has a plurality of lens elements 310 on a substrate 320. Thesubstrate 320 has an upper substrate surface 321 and an opposite lower substrate surface 322.The lens elements 310 are provided on the upper substrate surface 321.In Figure 3, the plurality of lens elements 310 is arranged in a regular two- dimensional array. However, for the purpose of the invention, the plurality of lens elements may be arranged in any suitable way, whether regular or irregular, and whether one- dimensional or two-dimensional. Furthermore, the plurality of lens elements may have any2024PF80248 7suitable number of lens elements, such as less than 10, or a few tens, or a few hundreds, or even a few thousand. Each lens element 310 has a convex outer surface and is hence arranged tonarrow the angular distribution of a light beam by means of refraction.The lens elements 310 may be plano-convex lenses, although it is not necessary that they have a flat surface at a side facing the substrate 320. Instead, the surfaceat the side facing the substrate 320 may be a concave surface. In this case, the lens elements310 have a kind of cavity at the side facing the substrate 320, for example to accommodate (part of) a light emitting element. Each lens element 310 of the lens plate 300 has an optical axis 330, being animaginary straight line that is oriented perpendicular to the substrate 320 and that passesthrough the geometrical center of the associated lens element 310. Each lens element 310 has a lower part 311 and an upper part 312. The lowerpart 311 is adjacent to the substrate 320. The upper part 312 is arranged on top of the lowerpart 311 in a direction away from the substrate 320. Each lower part 311 has an outer surface extending around the optical axis330. The outer surface of the lower part 311 is provided with a surface texture. The upperparts 312 are all transparent (or clear).Figure 4 shows a close-up of one of the lens elements 310. The lens element 310 has a lower part 311 and an upper part 312. The lowerpart 311 has an outer surface extending around the optical axis 330. The outer surface of the lower part 311 is provided with a surface texture. The upper part 312 is transparent. The lens element 310 has a first height ℎ^. The upper part 312 has a secondheight ℎ^. The first height ℎ^ and the second height ℎ^ are both measured in a direction alongthe optical axis 330.The upper part 312 of the lens element 310 shown in Figure 4 is a sphericalcap. A spherical cap is a part of a sphere which lies above (or below) a given plane. If theplane passes through the center of the sphere, the spherical cap is a hemisphere. The lower part 311 of the lens element 310 shown in Figure 4 is a spherical segment. A spherical segment is a part of a sphere defined by cutting the sphere with a pair of parallel planes. Because a spherical segment can be thought of as a spherical cap with the top truncated, it may also be referred to as a spherical frustum.2024PF80248 8Being a spherical segment, the lower part 311 has a first base radius ^^ and asecond base radius ^^. The first base radius ^^is at a first side of the lower part 311, and the second base radius ^^is at a second side of the lower part 311, being opposite to the first side of the lower part 311. The first side of the lower part 311 is the side that faces the substrate 320, and the second side of the lower part 311 is the side that faces away from the substrate 320. As previously mentioned, it is not necessary for the purpose of the invention that the lens elements have a flat surface at a side facing the substrate. The same holds true for the lens 310 shown in Figure 4. In other words, at the first side of the lower part 311, there may be a cavity, or, in general, a non-flat surface that curves inwards. If this would be the case, the lower part 311 should still be considered a spherical segment, because there is no impact on the outer surface of the lower part 311, which is still that of a spherical segment. When the lens element 310 has a shape as shown in Figure 4, there is a relationbetween the height ratio ℎ^⁄ ℎ^ and the base ratio ^^⁄ ^^ .The height ratio ℎ^⁄ ℎ^ can have any value between 0 and 1. When the heightratio ℎ^⁄ ℎ^ is equal to 0, ℎ^ is equal to 0, which essentially means that there is no upper part312. When the height ratio ℎ^⁄ ℎ^ is equal to 1, ℎ^ is equal to which essentially meansthat there is no lower part 311. When the height ratio ℎ^⁄ ℎ^ is equal to 0, the base ratio ^^⁄ ^^ is also equal to0, and when the height ratio ℎ^⁄ ℎ^ is equal to 1, the base ratio ^^⁄ ^^ is also equal to 1.For intermediate values of the height ratio ℎ^⁄ ℎ^ (i.e., values between 0 and1), the base ratio ^^⁄ ^^ can have any value from a range of values. This range of values has alower limit and an upper limit, which are given by the following equations: The above equations can be derived from Figure 5, showing a hemisphere with radius ^. The part of the hemisphere with height ℎ^corresponds to the lens element 310, the shaded part of the hemisphere corresponds to the lower part 311 of the lens element 310, and the part with height ℎ^corresponds to the upper part 312 of the lens element 310.2024PF80248 9Using the Pythagorean theorem: ^^^ + (^ − ℎ )^ = ^^^ = ^^^ + (^ − ℎ^)^ The above can be rearranged to: The upper limit of the base ratio ^^⁄ ^^ corresponds to a situation wherein ℎ^ isequal to ^. In other words, when the lens element 310 is a hemisphere. The lower limit of the base ratio ^^⁄ ^^ corresponds to a situation wherein ℎ^(and hence also ℎ^) approaches 0. Figure 6 shows a graph of the base ratio ^^⁄ ^^ as a function of the height ratioℎ^⁄ ℎ^ . In this graph, the solid line 600 marks the area wherein the possible values for thebase ratio ^^⁄ ^^ can be found.According to the invention, the height ratio ℎ^⁄ ℎ^ should be at least 0,1 butnot more than 0,7. In other words, 0,1 ≤ ℎ^⁄ ℎ^ ≤ 0,7.The height ratio ℎ^⁄ ℎ^ should be at least 0,1, such as at least 0,2, or at least0,3. The height ratio ℎ^⁄ ℎ^ should not be more than 0,7, such as not more than 0,6, or notmore than 0,5. The lower limit of 0,1 for the height ratio ℎ^⁄ ℎ^ ensures that the lens elementhas a sufficiently large transparent upper part, while the upper limit of 0,7 ensures that thelens element has a sufficiently large textured lower part. In other words, the range for theheight ratio ℎ^⁄ ℎ^ represents an optimum wherein on the one hand glare requirements can bemet, while on the other hand color-over-angle effects can be prevented. When the lens element 310 has a shape as shown in Figure 4, it is preferredthat the base ratio ^^⁄ ^^ is at least 0,5, such as at least 0,6, or at least 0,7. This ensures that thetextured lower part 311 has a relatively low impact on a main part of the beam shape, whilestill being arranged to sufficiently reduce undesired color-over-angle effects. The shaded area610 shown in the graph of Figure 6 therefore indicates a preferred parameter space for a lenselement 310 that has a shape as shown in Figure 4.2024PF80248 10The lens elements 310 of the lens plate 300 shown in Figure 3 each have alower part 311 and an upper part 312. The lower part 311 has an outer surface extendingaround the optical axis 330 of the respective lens element 310. This outer surface is provided with a surface texture. The surface texture can be defined by means of an arithmetic averageroughness (also referred to as the Ra value), which indicates the average surface roughnessfor the length of the measurement performed. In other words, it is the average difference between peaks and valleys. Suitable surface textures are VDI 3400 grades 10 to 30. VDI 3400 refers to a mold texture standard set by VDI (Verein Deutscher Ingenieure), the Society of German Engineers. The VDI 3400 standard covers 45 grades of textures, from VDI 3400 grade 0 (Ra value of 0,10 micrometers) to grade 45 (Ra value of 18,00 micrometers), wherein grade 0corresponds to a surface texture with an arithmetic average roughness of 0,10 micrometers,and grade 45 to a surface texture with an arithmetic average roughness of 18 micrometers.VDI 3400 grade 10 corresponds to a surface texture with an arithmetic average roughness of0,32 micrometers, and VDI 3400 grade 30 corresponds to a surface texture with an arithmeticaverage roughness of 3,20 micrometers.For example, the surface texture may have an arithmetic average roughness ofat least 0,40 micrometers, corresponding to a VDI 3400 grade 12 surface texture. Othersuitable surface textures are VDI 3400 grades 15 (average roughness of 0,56 micrometers),18 (average roughness of 0,80 micrometers), 21 (average roughness of 1,12 micrometers), 24(average roughness of 1,60 micrometers), and 27 (average roughness of 2,20 micrometers).Based on the above, the surface texture may have an arithmetic averageroughness in a range of 0,3 to 3 micrometers, such as in a range of 0,4 to 2 micrometers.The requirement for the height ratio ℎ^⁄ ℎ^ represents an optimum wherein onthe one hand glare requirements can be met, while on the other hand color-over-angle effects can be prevented. In other words, a surface area of a lens element must be defined that has a relatively large impact on color-over-angle effects but a relatively low impact on UGR and L65 requirements. The surface to be defined mentioned above can be found be first simulating the performance of a non-textured (i.e., fully transparent or optically clear) lens element to findthe projected areas on a reference plane where undesired color-over-angle effects occur. Next,the light rays that are responsible for these undesired color-over-angle effects can be tracked2024PF80248 11to identify the surface area of the lens element from which they originate. This surface area should then be textured. The surface area of the lens element that should be textured may depend on various parameters, that may differ from one application to the other, such as the specific shape of the lens element, the material from which the lens elements are made, and thedistance between the lens element and any further optical element of the luminaire.However, the inventors found that when a lower part of the lens element istextured over its full circumference, while an upper part of the lens remains transparent, thedesired advantages can be achieved for the vast majority of applications when the upper parthas a height that is at least one tenth but not more than half the height of the lens element itself. The range of applications for which the desired advantages are achieved canbe extended even further when the textured part of the lens element is a spherical segmenthaving a first base radius at a first side facing the substrate, and a second base radius at asecond side facing away from the substrate, wherein a base ratio of the second base radius and the first base radius is at least 0,5. Figure 7 shows an exploded view of a luminaire 2000 that comprises a lensplate 300, being a lens plate according to the present invention. The lens plate 300 is similar to the lens plate 300 as shown in Figure 3, and as discussed in detail in the preceding text. As in the luminaire 1000 shown in Figure 1, in the luminaire 2000 of Figure 7 the lens plate 100 is arranged between the light engine 400 and the light diffusing cover 500. The luminaire 2000 may further comprise other components, such as a housing and a driver, but for the sake of clarity such further components are not shown in Figure 7. The light engine 400 comprises a plurality of light emitting elements 410 on a carrier 420, such as light emitting diodes (LEDs), or any other suitable light emitting element, on a printed circuit board (PCB), or on any other suitable carrier. Each lens element 310 of the lens plate 300 has an optical axis 330, and eachlight emitting element 410 of the light engine 400 is positioned on the optical axis 330 of anassociated lens element 310 of the lens plate 300.When the luminaire 2000 is in operation, each light emitting element 410 ofthe light engine 400 emits a primary light beam with a primary angular distribution. Thisprimary light beam is then incident on a lens element 310 of the lens plate 300.2024PF80248 12Upon passing the lens element 310, the primary light beam is converted into asecondary light beam with a secondary angular distribution. The secondary light beam thenpasses through the light diffusing cover 500, as a result of which it is converted into an output light beam. All output light beams together constitute the light output of the luminaire 2000. Figure 8 shows two photographs of different luminaires, each representing aview towards the cover plate of the luminaire. Photograph (a) is for a luminaire of the type shown in Figure 1 (i.e., a luminaire with a prior art lens plate, having clear lenses), while photograph (b) is for a luminaire of the type shown in Figure 7 (i.e., a luminaire with a lens plate according to the invention, having partially textured lenses). Figure 8 also shows the orientations of the so-called C0 / C180 and C90 / C270planes. These are planes of the C-plane system, wherein the common axis of the planes is represented by a vertical line passing through the center of the luminaire. The planes in the C-plane system (or, the C-planes) are defined in terms of the angle formed with the axis of theluminaire. The C0 / C180 plane is a plane oriented perpendicular to the elongation direction ofthe luminaire, while the C90 / C270 plane is a plane oriented parallel to the elongation direction of the luminaire. In the photographs of Figure 8, the dashed lines mark a central part of the cover plate. In photograph (a), dark horizontal stripes are visible in the marked central part of the cover plate, while in photograph (b) the corresponding marked central part has a homogeneous appearance. In a full-color version of photograph (a), the black horizontal stripes would be colored (blue and or yellow) lines on a white background. These colored lines are artefacts caused by undesired color-over-angle effects. Such undesired artefacts are absent in photograph (b), being prevented from occurring by the lens plate according to the invention. Figure 9 shows two polar luminous intensity diagrams.A polar luminous intensity diagram illustrates the distribution of luminousintensity, as measured in a cross-sectional plane of a luminaire. In addition to luminousintensity, the diagram provides a visual guide to the type of distribution expected from theluminaire. In the diagrams of Figure 9, the luminous intensity is expressed in candela per1,000 lumen, meaning the luminous intensity in candela (cd) assuming there would be 1,000lumen (lm) in the measured luminaire. This enables comparing different types of luminaires.2024PF80248 13The curves plotted in the diagrams of Figure 9 are measured in the C0 / C180plane (see Figure 8 for the orientation of the C0 / C180 plane).Under (a), Figure 9 shows the polar luminous intensity diagram when theluminaire has fully clear lenses, such as shown in Figure 1. Under (b), Figure 9 shows thepolar luminous intensity diagram when the luminaire has the partially textured lenses ofFigure 3. In other words, the diagram under (a) represents a luminaire with a prior art lensplate, and the diagram under (b) represents a luminaire with a lens plate according to theinvention. A comparison of the two polar luminous intensity diagrams shows that the distribution is in both cases more or less the same. In other words, replacing a prior art lens plate, having clear lenses, with a lens plate according to invention, having partially texturedlenses, does not have a significant influence on the distribution of a luminaire in the C0 / C180plane. For the sake of clarity, polar luminous intensity plots measured in the C90 / C270 planes are not included in the diagrams of Figure 9. These plots have been measured, and they also show no significant influence on the distribution of the luminaire. Figure 10 shows two plots of color point data. The data are representative ofcolor points in the CIE 1976 L’, u’, v’ color space, wherein the plots show the u’ and v’coordinates of the color points. In each plot, the points shown as crosses represent color points measured in the C0 / C180 plane, and those shown as open circles represent color points measured in the C90 / C270 plane. Plot (a) shows the u’ and v’ color coordinates of a luminaire with fully clear lenses (such as shown in Figure 1), while plot (b) shows the u’ and v’ color coordinates of a luminaire with partially textured lenses (such as shown in Figure 3). For each of the sets of color coordinates shown in plots (a) and (b) an average distance between the coordinates can be calculated. For plot (a), the calculated average distance is 0,87, and for plot (b) the calculated average distance is 0,75. The lower the average distance between the various color coordinates is, the more homogeneous the color will be. It is clear that by replacing a lens plate with fully clear lenses by a lens plate according to the invention, the color uniformity is improved.2024PF80248 14It should be noted that the above-mentioned embodiments illustrate rather thanlimit the invention, and that those skilled in the art will be able to design many alternativeembodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb “to comprise” and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article “a” or “an” preceding an element does not exclude the presence of a plurality of such elements. 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. The various aspects discussed in this patent can be combined in order to provide additional advantages. Further, the person skilled in the art will understand that embodiments can be combined, and that also more than two embodiments can be combined.

Claims

2024PF80248 15CLAIMS:

1. A lens plate (300) comprising a plurality of lens elements (310) on a substrate(320), wherein each lens element (310) has an optical axis (330) oriented perpendicular to thesubstrate (320), wherein each lens element (310) has a lower part (311) and an upper part(312), the lower part (311) being adjacent to the substrate (320), wherein the lower part (311)has an outer surface extending around the optical axis (330) and being provided with a surface texture, wherein the upper part (312) is transparent, wherein each lens element (310) has a first height, and each upper part (312) has a second height, the first height and thesecond height being measured along the optical axis (330), wherein a height ratio of thesecond height and the first height is at least 0,1 but not more than 0,7, wherein the upper part (312) is a spherical cap, and the lower part (311) is a spherical segment (320), wherein the spherical segment has a first base radius at a first side facing the substrate (320), and a second base radius at a second side facing away from the substrate (320), and wherein a base ratio of the second base radius and the first base radius is at least 0,5.

2. The lens plate (300) according to claim 1, wherein the height ratio of thesecond height and the first height is at least 0,3 but not more than 0,6.

3. The lens plate (300) according to any one of the preceding claims, wherein thebase ratio of the second base radius and the first base radius is at least 0,7.

4. The lens plate (300) according to any one of the preceding claims, wherein thesurface texture has an arithmetic average roughness in a range of 0,3 to 3 micrometers.

5. The lens plate (300) according to claim 4, wherein the arithmetic averageroughness is in a range of 0,4 to 2 micrometers.

6. A luminaire (2000) comprising the lens plate (300) according to any one ofclaims 1 to 5, wherein the luminaire (2000) further comprises a plurality of light emitting2024PF80248 16elements (410), each light emitting element (410) being positioned on the optical axis (330)of an associated lens element (310) of the lens plate (300).

7. The luminaire (2000) according to claim 6, wherein the luminaire (2000)comprises a light diffusing cover plate (500) provided over the lens plate (300).

8. The luminaire (2000) according to any one of claims 6 and 7, wherein the lightemitting elements (410) are light emitting diodes.

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