Patent Publication Number: US-10760770-B2

Title: Device for modifying light distribution

Description:
FIELD OF THE DISCLOSURE 
     The disclosure relates generally to illuminating engineering. More particularly, the disclosure relates to a device for modifying distribution of light produced by a light source that can be, for example but not necessarily, a light emitting diode “LED”. 
     BACKGROUND 
     Distribution of light produced by a light source can be important or even critical in some applications. The light source can be, for example but not necessarily, a light emitting diode “LED”, a filament lamp, or a gas-discharge lamp.  FIG. 1  shows a section view of an exemplifying device  101  according to the prior art for modifying the distribution of light produced by a light source  102 . The section plane is parallel with the xz-plane of a coordinate system  199 . The device  101  comprises a transparent body  103  that is made of transparent material such as for example acrylic plastic, polycarbonate, optical silicone, or glass. The transparent body  103  can be rotationally symmetric with respect to a geometric line  125 . It is, however, also possible that the transparent body  103  has a non-circular shape when seen along the z-axis of the coordinate system  199 . The transparent body  103  comprises a first surface  104  that acts as a light ingress surface, a second surface  105  that acts as a light egress surface, and a third surface  106  that constitutes a zone around the first surface and joins the first surface. The second  105  surface is configured to reflect, towards the third surface  106 , at least a part of light received via the first surface from the light source  102 . The third surface  106  is configured to reflect, towards the second surface  105 , the light reflected from the second surface so that the light penetrates the second surface  105 . In  FIG. 1 , some of the light beams produced by the light source  102  are depicted with dashed line arrows. 
     In many cases, there is a need to design a device of the kind illustrated in  FIG. 1  so that a combination of a light source and the device produces a desired illumination pattern on a surface being illuminated. For example, there might be a desire to avoid ring-shaped areas having higher and lower light intensities in the above-mentioned illumination pattern. An inherent challenge related to devices of the kind illustrated in  FIG. 1  is that the above-mentioned second and third surfaces  105  and  106  have to be shaped so that the condition for total internal reflection “TIR” is fulfilled at all locations on the third surface  106  because light should not leak out through the third surface  106 . This requirement limits the freedom to design the shapes of the second and third surfaces  105  and  106 , and thereby there may be a need for compromises. 
     SUMMARY 
     The following presents a simplified summary in order to provide a basic understanding of some aspects of various embodiments of the invention. The summary is not an extensive overview of the invention. It is neither intended to identify key or critical elements of the invention nor to delineate the scope of the invention. The following summary merely presents some concepts of the invention in a simplified form as a prelude to a more detailed description of exemplifying embodiments of the invention. 
     In this document, the word “geometric” when used as a prefix means a geometric concept that is not necessarily a part of any physical object. The geometric concept can be for example a geometric line, a geometric plane, a non-planar geometric surface, a geometric room, or any other geometric entity that is one, two, or three dimensional. 
     In accordance with the invention, there is provided a new device for modifying the distribution of light produced by a light source. A device according to the invention comprises a transparent body made of transparent material having refractive index greater than one. The transparent body comprises a first surface, a second surface on an opposite side of the transparent body with respect to the first surface, and at least one third surface joining the first surface, wherein:
         the second surface defines a cavity opening away from the first surface,   the second surface is configured to reflect, towards the third surface, at least a part of light received via the first surface,   the third surface is configured to reflect, towards the second surface, the light reflected from the second surface,   the second surface is configured to act as a light egress surface for the light reflected from the third surface, and   the third surface comprises at least one groove on a propagation path of a part of the light reflected from the second surface so that the part of the light reflected from the second surface propagates across the groove prior to being reflected from the third surface.       

     Distribution of light that exits the transparent body via the above-mentioned second surface can be tuned by adjusting the shape, the size, and/or the location of the at least one groove. Therefore, the at least one groove increases the degrees of freedom when designing the device in order to achieve a desired light distribution pattern. 
     In accordance with the invention, there is provided also a new illuminator system comprising at least one light source and at least one device according to the invention for modifying the distribution of light produced by each light source. Each light source can be, for example, a light emitting diode “LED”, a filament lamp, or a gas-discharge lamp. 
     In accordance with the invention, there is provided also a new mold having a form suitable for manufacturing, by mold casting, a piece of solid material, e.g. plastic, having a shape of a device according to the invention. 
     A number of exemplifying and non-limiting embodiments of the invention are described in accompanied dependent claims. 
     Various exemplifying and non-limiting embodiments of the invention both as to constructions and to methods of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific exemplifying embodiments when read in connection with the accompanying drawings. 
     The verbs “to comprise” and “to include” are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in dependent claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of “a” or “an”, i.e. a singular form, throughout this document does not exclude a plurality. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The exemplifying and non-limiting embodiments of the invention and their advantages are explained in greater detail below with reference to the accompanying drawings, in which: 
         FIG. 1  illustrates a device according to the prior art for modifying light distribution, 
         FIGS. 2 a  and 2 b    illustrate a device according to an exemplifying and non-limiting embodiment of the invention for modifying light distribution, 
         FIG. 3  illustrates a detail of a device according to another exemplifying and non-limiting embodiment of the invention for modifying light distribution, 
         FIG. 4  illustrates a device according to an exemplifying and non-limiting embodiment of the invention for modifying light distribution, and 
         FIGS. 5 a  and 5 b    illustrate operation of a device according to an exemplifying and non-limiting embodiment of the invention for modifying light distribution. 
     
    
    
       FIG. 1  has already been explained in the Background-section of this document. 
     DESCRIPTION OF EXEMPLIFYING EMBODIMENTS 
     The specific examples provided in the description given below should not be construed as limiting the scope and/or the applicability of the appended claims. Lists and groups of examples provided in the description given below are not exhaustive unless otherwise explicitly stated. 
       FIG. 2 a    shows a section view of a device  201  according to an exemplifying and non-limiting embodiment of the invention for modifying the distribution of light emitted by a light source  202 . The light source  202  can be, for example but not necessarily, a light emitting diode “LED”, a filament lamp, or a gas-discharge lamp. The section shown in  FIG. 2 a    has been taken along a line A-A shown in  FIG. 2 b    which shows the device  201  when seen along the positive z-direction of a coordinate system  299 . The section plane is parallel with the xz-plane of the coordinate system  299 . The device  201  comprises a transparent body  203  made of transparent material having refractive index greater than one. The transparent material can be for example acrylic plastic, polycarbonate, optical silicone, or glass. The method of manufacture of the transparent body  203  can be for example mold casting. In the exemplifying case illustrated in  FIGS. 2 a  and 2 b   , the transparent body  203  is rotationally symmetric with respect to a geometric axis  225  that is parallel with the z-axis of the coordinate system  299 . It is, however, also possible that the transparent body of a device according to another embodiment of the invention has a non-circular shape when seen along the z-axis of the coordinate system  299 . Furthermore, it is also possible that at least a part of the transparent body of a device according to an embodiment of the invention has substantially a same cross-sectional shape on the whole length of the above-mentioned part of the transparent body. The cross-sectional shape can be for example similar to the shape of the section shown in  FIG. 2   a.    
     The transparent body  203  comprises a first surface  204 , a second surface  205 , and a third surface  206  joining the first surface  204 . The first surface  204  and the second surface  205  are located on opposite sides of the transparent body  203 . As shown in  FIG. 2 a   , the second surface  205  defines a cavity that opens away from the first surface  204 . In  FIG. 2 a   , some of the light beams produced by the light source  202  are depicted with dashed line arrows. As illustrated with the dashed line arrows, the second surface  205  is configured to reflect, towards the third surface  206 , at least a part of light received via the first surface  204 . The third surface  206  is configured to reflect, towards the second surface  205 , the light reflected from the second surface. The second surface  205  is configured to act as a light egress surface for the light reflected from the third surface  206 . The third surface  206  comprises a groove  207 . As illustrated in  FIG. 2 a   , a part of the light reflected from the second surface  205  propagates across the groove  207  prior to being reflected from the third surface  206 . In this exemplifying case where the transparent body  203  is rotationally symmetric, the groove  207  is circular as illustrated in  FIG. 2 b   . It is also possible that the third surface  203  is provided with two or more grooves. Distribution of light that exits the transparent body  203  via the second surface  205  can be tuned by adjusting the shape, the size, and/or the location of the one or more grooves on the third surface  206 . Thus, the one or more grooves increase the degrees of freedom when designing the transparent body  203  in order to achieve a desired light distribution pattern. 
     In the exemplifying device  201  illustrated in  FIGS. 2 a  and 2 b   , the cross-sectional profile of the groove  207  is substantially V-shaped. Depending on a desired light distribution pattern, it is however also possible that the cross-sectional profile of the groove needs to have another shape in order to achieve the desired light distribution pattern. For example, the groove could have a U-shaped cross-sectional profile. 
       FIG. 3  illustrates a groove  307  of a device according to an exemplifying and non-limiting embodiment of the invention for modifying light distribution. In  FIG. 3 , exemplifying light beams which propagate across the groove  307  are depicted with dashed line arrows. In this exemplifying case, the cross-sectional profile of the groove  307  has a substantially V-shaped bottom region, a first wall  317  of the groove which is closer to the first surface  304  has an arched cross-sectional profile so that the first wall  317  is convex, and a second wall  318  of the groove  307  which is farther from the first surface  304  has a substantially straight cross-sectional profile. It is also possible that both of the first and second walls of the groove have arched cross-sectional profiles so that the first and second walls are convex, or that the second wall which is farther from the first surface  304  has an arched cross-sectional profile so that the second wall is convex and the first wall which is closer to the first surface  304  has a substantially straight cross-sectional profile. 
     In the exemplifying device  201  illustrated in  FIGS. 2 a  and 2 b   , the cavity defined by the second surface  205  is substantially conical. Depending on a desired light distribution pattern, it is however also possible that the cavity needs to have a non-conical shape in order to achieve the desired light distribution pattern. A non-conical shape can be e.g. a shape of a paraboloid. 
     In the exemplifying device  201  illustrated in  FIGS. 2 a  and 2 b   , the first surface  204  has a substantially planar center zone  204   a  and a surrounding zone  204   b  defining a truncated cone whose coning angle opens towards the second surface  205 . It is also possible that the first surface is designed to comprise e.g. a cavity for acting as a place for the light source  202 . 
     The above-described device  201  and the light source  202  constitute an illuminator system according to an embodiment of the invention. The illuminator system further comprises mechanical support structures for supporting the device  201  and the light source  202 . The mechanical support structures are not shown in  FIGS. 2 a  and 2 b   . An illuminator system according to another embodiment of the invention may comprise for example an elongated device according to an embodiment of the invention for modifying the distribution of light emitted by an elongated light source or by a set of point-form light sources placed on a same geometric line. The cross-sectional shape of the transparent body of the elongated device can be e.g. similar to the shape of the section shown in  FIG. 2   a.    
       FIG. 4  shows a section view of a device  401  according to an exemplifying and non-limiting embodiment of the invention for modifying the distribution of light emitted by a light source  402 . The section plane is parallel with the xz-plane of a coordinate system  499 . In  FIG. 4 , some of the light beams produced by the light source  402  are depicted with dashed line arrows. The device  401  comprises a transparent body  403  made of transparent material having refractive index greater than one. The transparent body  403  comprises a first surface  404 , a second surface  405 , and a third surface  406  joining the first surface  404 . The first surface  404  and the second surface  405  are located on opposite sides of the transparent body  403 . The third surface  406  comprises a groove  407  so that a part of the light reflected from the second surface  405  propagates across the groove  407  prior to being reflected from the third surface  406 . 
     In the exemplifying device  401  illustrated in  FIG. 4 , a part of the second surface  405  comprises undulations  408  suitable for modifying the distribution of light that penetrates the above-mentioned part of the second surface  405 . The undulations may comprise converging and diverging deviations from a smooth shape so that the surface provided with the undulations is a color mixing surface. In a color mixing surface, light beams exhibiting different wavelengths are effectively mixed thus producing a light distribution pattern which contains all wavelengths evenly distributed across the light distribution pattern. In the exemplifying case illustrated in  FIG. 4 , the undulations  408  are grooves and ridges between the grooves, where the grooves and ridges extend from the edge of the second surface  405  towards the bottom of the conical cavity defined by the second surface  405 . 
       FIGS. 5 a  and 5 b    illustrate a functional difference between a first device which is similar to the above-described device  401  and a second device which is otherwise similar to the first device but there is no groove similar to the groove  407 . In  FIG. 5 a   , curves  520  and  521  present luminous intensities, i.e. luminous power per a unit solid angle, as functions of a polar angle α that is illustrated in  FIG. 4 . The curve  520  presents the luminous intensity in a first case where the first device modifies the distribution of light emitted by a light source, and the curve  521  shows the luminous intensity in a second case where the second device modifies the distribution of light emitted by the same light source or by a similar light source. As can be seen, the luminous intensity in the positive z-direction of the coordinate system  499 , i.e. α=0, is significantly higher when using the first device having the groove than when using the second device which does not have a groove. When using the first device, the surfaces of the groove change the propagation direction of light which propagates across the groove and thereby less light leaks out trough surfaces on which total internal reflection “TIR” is meant to take place. Thus, the efficiency of the first device is higher than that of the second device.  FIG. 5 b    illustrates an illumination pattern  522  produced on a planar surface by using the first device and a corresponding illumination pattern  523  produced on a planar surface by using the second device. As can be seen, the illumination pattern  523  has a ring-shaped area having a local intensity maximum whereas the illumination pattern  522  is practically free from such ring-shaped areas. 
     The specific examples provided in the description given above should not be construed as limiting the scope and/or the applicability of the appended claims. Lists and groups of examples provided in the description given above are not exhaustive unless otherwise explicitly stated.