WO2010094141A1

WO2010094141A1 - Glare reduction in led lighting systems

Info

Publication number: WO2010094141A1
Application number: PCT/CA2010/000258
Authority: WO
Inventors: Eran Plonski; Sharath Kumar; Eihab Baqui
Original assignee: Phoster Industries
Priority date: 2009-02-20
Filing date: 2010-02-22
Publication date: 2010-08-26

Abstract

There is described a method for reducing glare in a lighting system, the method comprising: propagating a light beam of at least one light-emitting diode (LED) through a corresponding lens mounted to a light transmitting support; and illuminating at least a portion of the light transmitting support, thereby reducing a difference in brightness between the corresponding lens and the light transmitting support.

Description

GLARE REDUCTION IN LED LIGHTING SYSTEMS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority under 35 USC§ 119 (e) of US Provisional Patent Application bearing serial number 61/154,312, filed on February 20, 2009, the contents of which are hereby incorporated by reference.

TECHNICAL FIELD

[0002] The present invention relates to the field of LED- based lighting systems, and more particularly to methods and devices for reducing glare generated in LED-based lighting systems .

BACKGROUND

[0003] Light-emitting diodes (LEDs) are presently used in lighting systems in replacement of conventional lighting technologies such as gas discharge lamps, incandescent bulbs and fluorescent lighting systems. LEDs present numerous advantages over conventional lighting technologies, such as longer lifetime, higher efficiency, lower energy consumption, and the ability to control the color of the emitted light.

[0004] LEDs are light emitters which emit high luminous flux light from a small area. The light emitted by an LED may be seen as more intense than the light emitted by a standard incandescent light. As a result, a person located in a room illuminated by an LED lighting system may be dazzled when his field of view crosses the LED lighting system. The glare caused by the LEDs may be problematic when these LEDs are used to illuminate certain environments, such as a working environment for example .

[0005] Therefore, there is a need for a method of reducing glare in LED lighting systems.

SUMMARY

[0006] According to a first broad aspect, there is provided a method for reducing glare in a lighting system, the method comprising: propagating a light beam of at least one light-emitting diode (LED) through a corresponding lens mounted to a light transmitting support; and illuminating at least a portion of the light transmitting support, thereby reducing a difference in brightness between the corresponding lens and the light transmitting support.

[0007] According to a second broad aspect, there is provided a lighting system comprising: a lens assembly comprising a light transmitting support and at least one illumination lens,- at least one light-emitting diode (LED) substantially aligned below a corresponding one of the at least one illumination lens and adapted to emit an illumination light beam projected on at least part of the corresponding illumination lens,- and a support illuminating device adapted to project light to at least part of the light transmitting support, thereby reducing a difference in brightness between the at least one illumination lens and the light transmitting support

[0008] According to another broad aspect, there is provided a diffuser for reducing glare in a light emitting diode (LED) lighting system, the diffuser comprising a lens having a light receiving surface for receiving a light beam from at least one LED, an opposite light transmitting surface for transmitting at least one part of the light beam, and a reflecting element adapted to partially reflect the light beam radially towards regions of the lens that do not receive the light beam directly from the at least one LED.

[0009] According to a further embodiment, there is provided a method for reducing glare in a lighting system, comprising: projecting a light beam emitted from at least one light emitting diode (LED) on a lens,- and partially reflecting within the lens the light beam radially towards darker regions of the lens that do not receive the light beam directly from the at least one LED, thereby reducing a difference in brightness between the darker regions of the lens and directly illuminated regions of the lens.

[0010] The expression "light transmitting" material or object refers to a material or object being transparent or translucent at a visible spectrum wavelength. In other words, a light transmitting object or material is non-opaque and allows at least a partial transmission of light having a visible spectrum wavelength. It should be understood that, in the case of an object, the dimensions of the object are chosen so that the object is non-opaque at the visible spectrum wavelength.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Further features and advantages of the present invention will become apparent from the following detailed description, taken in combination with the appended drawings, in which: [0012] Fig. 1 illustrates a lighting system according to the prior art in which the coupling of light into a lens is maximized;

[0013] Fig. 2 is a flow chart of a method for reducing glare in a lighting system comprising at least one lens mounted to a light transmitting support, in accordance with an embodiment ;

[0014] Fig. 3 is a perspective view of a lens assembly, in accordance with an embodiment;

[0015] Fig. 4 is a cross-sectional side view of a lighting system in which a distance between LEDs and a lens assembly is extended in comparison with the lighting system of Fig. 1, in accordance with an embodiment;

[0016] Fig. 5 is a cross-sectional side view of a lighting system in which a light beam emitted by LEDs is expanded, in accordance with an embodiment;

[0017] Fig. 6 is a cross-sectional side view of a lighting system comprising multiple additional LEDs, in accordance with an embodiment;

[0018] Fig. 7 is a cross-sectional side view of a lighting system comprising a single additional LED, in accordance with an embodiment ;

[0019] Fig. 8 is a flow chart of a method of reducing glare in an LED system by internally reflecting light within a lens, in accordance with an embodiment; [0020] Fig. 9 is a perspective view of a diffuser having a protrusion, in accordance with an embodiment;

[0021] Fig. 10 is a front view of the diffuser of Fig. 9;

[0022] Fig. 11 is a top view of the diffuser of Fig. 9 when positioned on top of an LED board, in accordance with an embodiment ;

[0023] Fig. 12 is a cross-sectional view of the assembly of Fig. 11;

[0024] Fig. 13 is a front view of a diffuser having no protrusion, in accordance with an embodiment; and

[0025] Fig. 14 illustrates a diffuser comprising a reflecting plate embedded therein, in accordance with an embodiment .

[0026] It will be noted that throughout the appended drawings, like features are identified by like reference numerals .

DETAILED DESCRIPTION

[0027] Figure 1 illustrates the positioning of a lens assembly 10 with respect to an LED 12 in an LED fixture, according to the prior art. The lens assembly 10 comprises a lens 14 assembled on a support 16. The distance W between the LED 12 and the lens 14, and the solid angle α of the light beam 18 emitted from the LED 12 are defined to optimize the coupling of light emitted by the LED 12 into the lens 14 so that substantially all of the light beam 18 is collected by the lens 14. The distance W and the solid angle α of the beam 18 are adequately chosen such that a maximum amount of light emitted by the LED 12 is coupled into the lens 14. In other words, when the light beam 18 emitted by the LED 12 reaches the lens 14, the surface area of the cross-section of the light beam 18 substantially equals the surface area of the lens 14. Alternatively, the surface area of the cross-section of the light beam 18 is inferior to that of the lens 14. The lens 14 transforms the light beam 18 into an expanded light beam 20. Alternatively, the lens 14 may be a converging lens to contract the light beam 18. Since the support 16 is not illuminated by the LED 12, there is a difference in brightness between the lens 14 and the support 16. Therefore, such an LED lighting system creates glare.

[0028] Figure 2 illustrates one embodiment of a method 30 for reducing glare in an LED lighting system. The first step 32 consists in propagating a light beam of at least one LED through a corresponding lens mounted to a light transmitting support .

[0029] Figure 3 illustrates one embodiment of an adequate light transmitting lens assembly 40 which may be used while performing the method 30. The assembly 40 comprises lenses 42 mounted on a light transmitting support 44.

[0030] In one embodiment, lenses 42 are independent from the support 44, which has a shape adapted to receive the lenses 42. Glue can be used to secure the lenses 42 on the support 44. Alternatively, each lens 42 may be screwed in the support 44. It should be understood that any mechanical means can be used to secure the lenses 42 on the support 44. In another embodiment, the lenses 42 and the support 44 are made of a single piece.

[0031] The lenses 42 and the support 44 can be made of any material having the property of transmitting light. For example, glass or transparent/translucent plastic can be used to make the lenses 42 and the support 44.

[0032] It should be understood that the lenses 42 may be any adequate type of lenses. For example, the lenses 42 may be converging lenses, diverging lenses, or the like.

[0033] While figure 3 illustrates a circular lens assembly 40 comprising seven lenses 42, it should be understood that any lens assembly comprising at least one lens mounted on a light transmitting support may be used. The lens assembly may have any shape and the lenses may be positioned at any adequate position on the support.

[0034] Referring back to step 32 of the method 30, the LEDS used for propagating the light beams correspond to the light sources used by the LED lighting system for illuminating a room, for example. Each LED is aligned substantially below a corresponding lens. The light beam emitted by each LED is collected by its corresponding lens which modifies the beam of light emitted by the LED. The modified beam is used for illumination of a room, for example .

[0035] Step 34 of the method 30 consists in illuminating at least a portion of the light transmitting support which reduces the contrast between the support and the lenses . The reduction of this contrast reduces glare generated by the LED lighting system.

[0036] In one embodiment, the illumination of the support is performed by adequately choosing the distance between the LEDs and the lens assembly as a function of the solid angle of the light beam emitted from each LED and the surface area of each lens such that the surface area of the cross-section of the light beam at the lens assembly is larger than that of the lens .

[0037] Figure 4 illustrates one embodiment of a lighting system 46 in which glare is reduced by moving LEDs 48 away from the lens assembly 40. In this embodiment, the solid angle αi of the beam 50 of each LED 48 is chosen such that the surface area of the cross-section of the beam 50 at the lens assembly 40 is inferior or substantially equal to that of the lens 42 when the LEDs 48 are located at a distance W_x from the lens assembly 40. In order to reduce glare, the LEDs 48 are positioned at a distance W₂ longer than the distance Wi such that the surface area of the cross-section of the beam 50 at the lens assembly 40 is larger than that of the lens 42. As a result, at least part of the light transmitting support 40 is illuminated by the light emitted from the LEDs 48, which reduces glare created by the lighting system 46 since the difference in brightness between the support 44 and the lenses 42 is reduced.

[0038] In one embodiment, the step 34 of the method 30 consists in expanding the light beam emitted from the LEDs so that at least a part of the light transmitting support is illuminated. [0039] Figure 5 illustrates one embodiment of a lighting system 60 in which glare is reduced by expanding the beam 50 emitted by each LED 48. In this embodiment, the LEDs 48 emitting the light beam 50 having a solid angle Cx₁ are positioned at the distance Wl from the lens assembly 40. A diverging lens 62 is positioned between each LED 48 and its corresponding lens 42 in order to convert the beam 50 into an expanded beam 64 having a solid angle greater than Cx₁. As a result, the beam 64 can be seen as a beam emitted by the LED 48 and having a solid angle larger than Ot₁ such that the surface area of the cross-section of the beam 64 at the lens assembly 40 is larger than that of the lens 42. It should be understood that any adequate beam expander known by a person skilled in the art may be used.

[0040] In another embodiment, the step 34 of illuminating the support is performed by inserting at least one additional LED positioned to illuminate the support. Figure 6 illustrates one embodiment of a lighting system 70 comprising additional LEDs 72 for reducing glare. The LEDs 48 emitting the beams 50 having the solid angle Cx₁ are positioned substantially below their corresponding lens 42 at the distance Wl such that the surface area of the cross-section of the light beam 50 at the lens assembly is inferior or substantially equal to that of the lens 42. The additional LEDs 72 are positioned below different parts of the light transmitting support 40. Each additional LED 72 emits a light beam 74 which illuminates a corresponding part of the support 40. The optical power of the light emitted by the LEDs 72 is adapted to illuminate the support 40 and reduce the difference in brightness between the lenses 42 and support 40.

[0041] While the lighting system 70 comprises several additional LEDs 72, Figure 7 illustrates one embodiment of a lighting system 80 comprising a single additional LED 92. The lighting system comprises a lens assembly 82, two LEDs 88 and the additional LED 92. The lens assembly 82 comprises a light transmitting support 84 on which two lenses 86 are mounted. The LEDs 88 are aligned with their corresponding lens 86 and are used as illumination sources. Each LED 88 emitting a beam 90 having a particular solid angle is substantially aligned with its corresponding lens 86 and positioned at an adequate distance from its corresponding lens 86 so that the surface area of the cross-section of the light beam 90 at the lens assembly 82 is inferior or substantially equal to that of the lens 86. The additional LED 92 emits a light beam 94 adapted to illuminate the majority of the support 84, thereby reducing the difference in brightness between the lenses 86 and the support 84.

[0042] In one embodiment, only regions of the light transmitting support surrounding the lenses are illuminated for reducing glare. Alternatively, only regions away from the lenses are illuminated. In another embodiment, the whole light transmitting support is illuminated.

[0043] It should be understood that a combination of the methods for reducing glare presented above may be used. For example, at least one additional glare reduction LED may be provided in the lighting system while the solid angle of the beams emitted by the LEDs used for illumination is increased. It should also be noted that the method may be applied to any LED lighting system comprising a light transmitting support and any number of lenses/LEDs.

[0044] In one embodiment, the LEDs 48 are mounted to an LED board and the lens assembly 40 is provided with risers extending from the surface of the lens assembly 40 facing the LEDs 48. The risers may be fixedly and removably secured to the LED board. The length of the risers is chosen to provide an adequate distance between the LEDs 48 and the lenses 42. If the lighting system comprises at least one additional glare reducing LED 72 and/or at least one beam expanding lens 2, the length of the risers may be chosen so that the distance between the LEDs 48 and the lenses 42 equals Wl. Alternatively, the length of the risers may be chosen so that the distance between the LEDs 48 and the lenses 42 equals W2.

[0045] While the present description refers to lighting systems in which the number of illumination LEDs is equal to the number of lenses, it should be understood that the number of lenses can be greater than the number of illumination LEDs. In this case, some lenses would not be used in the lighting system.

[0046] Figure 8 illustrates one embodiment of a method 96 for reducing glare in an LED lighting system. The first step 97 consists in projecting a light beam emitted from at least one LED on a lens . The lens may be any adequate lens adapted to receive and transmit the light beam from the LED. For example, the LEDs are located at an adequate distance from the lens so that the lens may expand or contract the received light beams. [0047] The light beam of the LED passes through some regions of the lens, thereby illuminating these regions, while the other regions of the lens are not traversed by the light beam and appear darker than the illuminated regions of the lens. This difference in brightness between the illuminated regions and the darker regions causes glare.

[0048] The second step 98 consists in partially reflecting within the lens the light beam emitted by at least one LED which passes through the lens. The light beam is radially reflected so that a portion of the light beam is directed towards the darker regions of the lens that do not receive the light beam directly from the LED in order to illuminate the darker regions. The illumination of the darker regions reduces the difference in brightness between the darker regions and the directly illuminated regions of the lens, which reduces glare generated by the lighting system.

[0049] Figures 9 and 10 illustrate one embodiment of a diffuser 100 which may be used as a suitable lens for the method 96 for reducing glare in an LED lighting system. The diffuser 100 comprises a circular diffusing lens 102 having a conical recess 104 and a substantially cylindrical protrusion 106. The protrusion 106 extends from a bottom surface of the diffusing lens 102 and is positioned at the center of the diffusing lens 102. The protrusion 106 comprises an LED recess 108 on its bottom surface. The LED recess 108 has a shape adapted to receive an LED. The conical recess 104 is also positioned at the center of the diffusing lens 102 such that the center of the conical recess 104 is substantially aligned with the center of the protrusion 106. The conical recess 102 extends from a top surface of the diffusing lens and penetrates partially the protrusion 106. The diffuser 100 is also provided with risers 110 that extend from the bottom surface of the lens 102 in order to be deposited on top of an LED board.

[0050] Figures 11 and 12 illustrate the diffuser 100 positioned on top of an LED board 112. The LED board 112 comprises six LEDs 114 positioned along a circle on the board 112 and an LED 116 is positioned at the center of the circle. Each LED 114 is provided with a lens 118 on its top surface while the central LED 116 has no lens.

[0051] As illustrated in Figure 12, the light 120 emitted by the LEDs 114 crosses the lens 102 without any substantial deviation while the light emitted by the central LED 116 is only partially transmitted by the lens 102. When it encounters the angled walls surrounding the conical recess 104, the beam of light emitted by the central LED 116 is divided into a transmitted beam 122 of light and a reflected beam 124 of light due to the reflecting index difference between air and the lens 102. The angle of the walls surrounding the conical recess 104 is chosen such that at least a partial reflection of the generated beam occurs. The beam 124 propagates inside the lens 102 and illuminates the lens 102. The illumination of the lens 102 reduces the contrast between the areas of the lens 102 facing an LED 114 and the areas of the lens 102 which do not face an LED 114. The reduction of this contrast reduces glare generated by the LED lighting system.

[0052] In one embodiment, the walls surrounding the recess 104 may be coated with a reflecting material in order to increase or decrease the proportion of the light beam internally reflected.

[0053] In one embodiment, the LEDs 114 are provided with no lens 118 and the diffuser is adapted to collect and transmit the light generated by the LEDs 114.

[0054] It should be understood that the LEDs 114 and 116 can have any layout on the board 112 as long as at least one LED faces the conical recess 104 when the diffuser 100 is positioned on top of the board 112.

[0055] While the circular lens 102 is provided with a convex top surface, it should be understood that the top surface can have other adequate shapes. For example, the lens 102 can be provided with a flat top surface. In addition, the lens 102 can be rectangular, triangular, square, etc.

[0056] It should be understood that the board 112 can be provided with any number of LED as long as one LED faces the recess 104. For example, the board can be provided with a single LED, i.e. LED 116.

[0057] While the diffuser 100 comprises a single conical recess 104, it should be understood that the lens 102 can have more than one conical recess 104 which can be positioned anywhere on the lens 102. In this case, an LED is positioned below each conical recess 104 when the diffuser 100 is positioned on top of an LED board 112.

[0058] The lens 102 and the protrusion 106 can be made of any light transmitting material. For example, glass or transparent/translucent plastic can be used to make the lenses 102 and the protrusion 106. [0059] Figure 13 illustrates one embodiment of a diffuser 130 for reducing glare in LED lighting systems. The diffuser 130 comprises a lens 132 provided with a conical recess 134. The conical recess 134 extends from the top surface of the lens 132 through part of its width. An LED is positioned substantially below the center of the conical recess 134 such that part of its generated light propagates inside the lens 132. The diffuser 130 also comprises risers 136 which extend from the bottom surface of the lens 132 in order to be positioned on top of an LED board.

[0060] It should be understood that the LEDs 12, 68, 88 and 114 can comprise various optics such as lenses which are not shown in the figures. As the beam of light emitted by an LED has a wide solid angle, at least one lens can be used for contracting the emitted beam of light, before further expanding the beam to the desired solid angle. Multiple lenses can be used in combination to create a beam of light having a desired solid angle. The beam may be expanded and/or contracted multiple times before reaching the support 44, 84.

[0061] While the present description refers to the provision of a recess on a lens for partially reflecting a light beam, it should be understood that any adequate reflecting device adapted to radially reflect at least a portion of a light beam within the lens towards the darker regions of the lens may be used. For example, a reflecting conical plate 142 may be embedded within the lens 140 as illustrated in Figure 14. The material and/or reflecting index of the material of the reflecting conical plate 142 is chosen so that a light beam emitted by an LED located below the plate 142 is partially reflected radially towards darker regions of the lens 140. Alternatively, the conical plate 142 may be replaced by a solid body cone made from an adequate material for partially reflecting a light beam.

[0062] While the present description refers to a conical reflecting element for radially reflecting at least a portion of a light beam within a lens, it should be understood that the reflecting element may have any other adequate shape to radially reflect a part of the light beam. For example, the reflecting element may have a truncated conical shape, a pyramidal shape, a truncated pyramidal shape, or the like.

[0063] It should be noted that the embodiments of the invention described above are intended to be exemplary only. The present invention can be carried out as a method or can be embodied in a lighting system. The scope of the invention is therefore intended to be limited solely by the scope of the appended claims.

Claims

I/WE CLAIM:

1. A method for reducing glare in a lighting system, said method comprising:

propagating a light beam of at least one light-emitting diode (LED) through a corresponding lens mounted to a light transmitting support; and

illuminating at least a portion of said light transmitting support, thereby reducing a difference in brightness between said corresponding lens and said light transmitting support.

2. The method of claim 1, wherein said illuminating comprises illuminating at least a portion of said light transmitting support using at least one additional LED.

3. The method of claim 1, wherein said illuminating comprises expanding said light beam emitted by said at least one LED.

4. The method of claim 1, wherein said propagating and said illuminating are concurrently performed by positioning said at least one illumination LED at a given distance from said corresponding lens so that a surface area of a cross-section of said light beam at said corresponding lens is superior to a surface area of said corresponding lens .

5. A lighting system comprising:

a lens assembly comprising a light transmitting support and at least one illumination lens; at least one light-emitting diode (LED) substantially aligned below a corresponding one of said at least one illumination lens and adapted to emit an illumination light beam projected on at least part of said corresponding illumination lens,- and

a support illuminating device adapted to project light to at least part of said light transmitting support, thereby reducing a difference in brightness between said at least one illumination lens and said light transmitting support.

6. The lighting system of claim 5, wherein said support illuminating device comprises at least one glare reducing LED positioned below said light transmitting support and adapted to illuminate said at least part of said light transmitting support .

7. The lighting system of claim 5, wherein said support illuminating device corresponds to at least one of said at least one light emitting diode positioned at a distance from said corresponding lens to illuminate both said corresponding one of said at least one illumination lens and said part of said light transmitting support concurrently.

8. The lighting system of claim 5, further comprising at least one diverging lens positioned between one of said at least one LED and a corresponding illumination lens, said at least one diverging lens and a corresponding LED forming said support illuminating device, said diverging lens adapted to expand a light beam emitted from said corresponding LED to illuminate both said corresponding illumination lens and said at least part of said light transmitting support concurrently .

9. The lighting system of any one of claims 5 to 8 , wherein said lens comprises risers adapted to position said lens with respect to said at least one LED.

10. A diffuser for reducing glare in a light emitting diode (LED) lighting system, said diffuser comprising a lens having a light receiving surface for receiving a light beam from at least one LED, an opposite light transmitting surface for transmitting at least one part of said light beam, and a reflecting element adapted to partially reflect said light beam radially towards regions of said lens that do not receive said light beam directly from said at least one LED.

11. The diffuser as claimed in claim 11, wherein said lens comprises an inwardly contracting shaped recess located on said light transmitting surface and said reflecting element comprises walls surrounding said inwardly contracting shaped recess .

12. The diffuser as claimed in claim 11, wherein said reflecting element comprises an inwardly contracting shaped plate inserted within said lens .

13. The diffuser as claimed in claim 11, wherein said reflecting element comprises an inwardly contracting shaped body inserted within said lens.

14. The diffuser as claimed in any one of claims 11 to 14, wherein the lens further comprises at least one protrusion extending from a light receiving surface of said lens and facing said reflecting element, said protrusion having an LED recess on a bottom side to receive a corresponding one of said at least one LED.

15. The diffuser as claimed in any one of claims 11 to 15, further comprising risers extending from said light receiving surface for positioning said lens with respect to said at least one LED.

16. A method for reducing glare in a lighting system, comprising:

projecting a light beam emitted from at least one light emitting diode (LED) on a lens; and

partially reflecting within said lens said light beam radially towards darker regions of said lens that do not receive said light beam directly from said at least one LED, thereby reducing a difference in brightness between said darker regions of said lens and directly illuminated regions of said lens .

17. The method as claimed in claim 17, wherein said partially reflecting said light beam comprises partially reflecting said light beam on walls surrounding an inwardly contracting shaped recess located on said light transmitting surface .

18. The method as claimed in claim 17, wherein said partially reflecting said light beam comprises partially reflecting said light beam on an inwardly contracting shaped plate inserted within said lens .

19. The method as claimed in claim 17, wherein said partially reflecting said light beam comprises partially reflecting said light beam on an inwardly contracting shaped body inserted within said lens .