Lighting Device with Transparent Substrate and Heat Sink

Abstract

A lighting device includes a heat sink having fins on a first side and a mounting surface of a second side opposite the first side. A substrate is attached to the mounting surface of the heat sink and a number of LEDs attached to the substrate. A single transparent substrate overlies all LEDs attached to the substrate. The transparent substrate includes a number of optical elements, each optical element overlying an associated one of the LEDs.

Description

TECHNICAL FIELD

The following disclosure relates to lighting systems and, more particularly, to lighting systems using light emitting diodes to externally illuminate signs.

SUMMARY

The present invention, in one aspect thereof, comprises a back panel for use in a light emitting diode (LED) lighting assembly. An extruded substrate formed of a thermally conductive material is provided, the substrate having a plurality of fins extending from a first side of the substrate, each of the fins having a substantially rectangular shape oriented so that a longitudinal axis of the fin is substantially parallel to a longitudinal axis of the substrate. At least some of the fins include a hole formed through the fin to enable heated air to rise through the fins. A plurality of LEDs are mounted on a second side of the substrate, and oriented in a longitudinal orientation with the fins oriented parallel to the bottom edge of a surface to be illuminated, such that heat rises perpendicular to the surface of the fin.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding, reference is now made to the following description taken in conjunction with the accompanying drawings in which:

FIG. 1A illustrates one embodiment of a billboard that may be externally lighted by one or more lighting assemblies;

FIGS. 1B-1D illustrate embodiments of angular positions of the lighting assembly of FIG. 1 relative to the billboard;

FIG. 2 illustrates one embodiment of a lighting assembly that may be used to light the billboard of FIG. 1;

FIGS. 3A and 3B illustrate one embodiment of a back panel that may be used in the lighting assembly of FIG. 2;

FIG. 3C illustrates one embodiment of the back panel of FIGS. 3A and 3B with a light panel and an optics panel that may also be used in the lighting assembly of FIG. 2;

FIGS. 4A and 4B illustrate one embodiment of a light panel that may be used with the lighting assembly of FIG. 2;

FIGS. 5A, 5B, 5C and 5D illustrate one embodiment of an optics panel that may be used with the lighting assembly of FIG. 2;

FIGS. 6A-6C illustrate a more detailed embodiment of the lighting assembly of FIG. 2;

FIGS. 7A and 7B illustrate an embodiment of a back panel that may be used with the lighting assembly of FIGS. 6A-6C;

FIG. 8A illustrates an embodiment of an LED assembly and an optics panel that may be used with the lighting assembly of FIG. 6;

FIGS. 8B-8J illustrates embodiments of the optics panel of FIG. 8A and optical elements that may be used to form part of the optics panel; and

FIG. 9 illustrates a more detailed embodiment of the lighting assembly of FIG. 2.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Billboards, such as those commonly used for advertising in cities and along roads, often have a picture and/or text that must be externally illuminated to be visible in low-light conditions. As technology has advanced and introduced new lighting devices such as the light emitting diode (LED), such advances have been applied to billboards. However, current lighting designs have limitations and improvements are needed. Although billboards are used herein for purposes of example, it is understood that the present disclosure may be applied to lighting for any type of sign that is externally illuminated.

Referring to FIG. 1A, one embodiment of a billboard 100 is illustrated. The billboard 100 includes a surface 102 onto which a picture and/or text may be painted, mounted, or otherwise affixed. The surface 102 may be any size, such as a commonly used size having a width of forty-eight feet wide and a height of fourteen feet. The surface 102 may be provided by placing a backing material on a frame 104 made of steel and/or other materials. The frame 104 may be mounted on one or more support poles 106, which may be considered part of the frame 104 or separate from the frame 104. The billboard 100 may include a walkway or other support structure 108 that enables the surface 102 to be more easily accessed.

One or more lighting assemblies 110 may be coupled to the walkway 108 (e.g., to a safety rail or to the walkway itself) and/or to another structural member of the billboard 100 to illuminate some or all of the surface 102 in low light conditions. The lighting assembly 110 may be mounted at or near a top edge 112 of the billboard 100, a bottom edge 114 of the billboard 100, a right edge 116 of the billboard 100, and/or a bottom edge 118 of the billboard 100. The lighting assembly 110 may be centered (e.g., located in approximately the center of the billboard 100) or off center as illustrated in FIG. 1A.

With additional reference to FIGS. 1B-1D, a surface 120 of the lighting assembly 110 may be parallel with respect to the surface 102 of the billboard 100 (FIG. 1B), may be perpendicular with respect to the surface 102 (FIG. 1C), or may be angled with respect to the surface 102 (FIG. 1D). It is understood that the lighting assembly 110 may be placed in many different orientations and locations relative to the billboard 100 and to one another, and the illustrated positions are only for purposes of example. Furthermore, it is understood that references to “top,” “bottom,” “left,” and “right” are used in the present disclosure for purposes of description and do not necessarily denote a fixed position. For example, the billboard 100 may be turned on end, and the referenced “top,” “bottom,” “left,” and “right” edges may still be readily identifiable although the “top” edge would be the “left” edge or the “right” edge.

One problem with current lighting technology is that it can be difficult to direct light only onto the surface 102 and even more difficult to do so evenly. This may be due partly to the placement of the lighting assembly 110, as shown in FIGS. 1B-1D. As the lighting assembly 110 is off center relative to the surface 102, light emitted from the lighting assembly 110 may not evenly strike the surface 102. One problem with uneven illumination is that certain parts of the surface 102 may be more brightly illuminated than other parts. This creates “hot spots” that may be undesirable. Attempting to evenly illuminate the surface 102 may cause light to be directed past the edges 112, 114, 116, and 118 as attempts are made to balance out hot spots in particular areas. However, light that does not strike the surface 102 is wasted and may create problems (e.g., light pollution), as well as waste illumination that could be used for the surface 102.

In addition to the difficulties of evenly illuminating the surface 102, the use of LEDs in an exterior lighting environment involves issues such as heat dissipation and protecting the LEDs against environmental conditions such as moisture. The presence of moving mechanical features such as fans that may be used to provide increased airflow for cooling may create additional reliability problems. Due to the difficulty and expense of replacing and/or repairing the lighting assembly 110 in combination with the desire to provide consistent lighting while minimizing downtime, such issues should be addressed in a manner that enhances reliability and uptime.

Referring to FIG. 2, one embodiment of a lighting assembly 200 is illustrated. The lighting assembly 200 provides a more detailed embodiment of the lighting assembly 110 of FIG. 1. The lighting assembly 200 includes a back panel 202, a light panel 204 (e.g., a printed circuit board (PCB)) having a plurality of LEDs (not shown) mounted thereon, and an optics panel 206. As will be described below in more detailed examples, light from the LEDs of the light panel 204 may be directed by the optics panel 206 to illuminate the surface 102 of the billboard 100 of FIG. 1. The back panel 202 may be configured to serve as a supporting substrate for the light panel 204 and optics panel 206, as well as to dissipate heat produced by the LEDs.

It is understood that any of the back panel 202, light panel 204, and optics panel 206 may actually be two or more physical substrates rather than a single panel as illustrated in FIG. 2. Furthermore, it is understood that there may be additional panels positioned behind the back panel 202, in front of the optics panel 206, and/or between the back panel 202 and light panel 204 and/or between the light panel 204 and optics panel 206.

Referring to FIGS. 3A-3C, one embodiment of the back panel 202 is illustrated with a front surface 302 and a back surface 304. The back panel 202 includes a top edge 306, a bottom edge 308, a right edge 310, and a left edge 312. The panel 202 may be formed of one or more thermally conductive materials (e.g., aluminum) and/or other materials.

The front surface 302 provides a mounting surface for the light panel 204. In some embodiments, the front surface 302 of the panel 202 may include one or more protrusions 314a and 314b that are substantially parallel to the top edge 306. The protrusions 314a and 314b may be configured to protect the light panel 204 from moisture. Although only two protrusions 314a and 314b are illustrated, it is understood that a single protrusion may be provided or three or more protrusions may be provided. Furthermore, such protrusions may vary in length, shape (e.g., may have angled or curved surfaces), orientation, and/or location on the front surface 302.

Referring specifically to FIG. 3C, a light panel 204 and an optical panel 206 may be mounted under the protrusion 314a (FIG. 3C). Moisture running down the front surface 302 in the direction of arrow 316 may strike the protrusion 314a and be directed away from the light panel 204 and optical panel 206 as shown by arrow 318. Although not shown, moisture may also be directed length down the protrusion 314a. Accordingly, protrusion 314a may serve as a gutter and aid in directing moisture away from a joint 320 where the optical panel 206 abuts the front surface 302. This may be beneficial even when a moisture resistant compound is used to seal the joint 320. In embodiments where there are multiple light panels 204 arranged vertically on the front surface 302, there may be a protrusion positioned above each light panel 204. For example, the protrusion 314a may be positioned directly above one light panel 204 and the protrusion 314b may be positioned directly above another light panel 204.

Referring specifically to FIG. 3B, the back surface 304 may be configured to increase heat dissipation. For example, the back surface 304 may be configured with a heat sink provided by fins 322a-322N, where N denotes a total number of fins. The fins 322a-322N increase the surface area of the back surface 304, thereby providing for additional heat dissipation to the surrounding air. The fins 322a-322N may be formed as part of the panel 202 or may be otherwise coupled to the panel 202 (e.g., may be part of a discrete heat sink that is coupled to the back surface 304). Some or all of the fins 322a-322N may be angled, as shown by fins 322a and 322b. In some embodiments, holes (not shown) may be provided in some or all of the fins 322a-322N to aid in air circulation. In such embodiments, the holes may cause a chimney effect in which heated air rises through the holes and is replaced by cooler air. This may be particularly effective in environments where natural air movement is limited.

Referring to FIGS. 4A and 4B, one embodiment of a single PCB 402 of the light panel 204 is illustrated. In the present example, the light panel 204 may include multiple PCBs 402, although it is understood that any number of PCBs may be used based on design issues such as the amount of illumination needed, the amount of illumination provided by a single PCB 402, the size of the surface 102 of the billboard 100, and/or other factors. As shown in the present embodiment with a substantially rectangular cross-section, the PCB 402 includes a front surface 404, a back surface 406, a top edge 408, a bottom edge 410, a right edge 412, and a left edge 414.

The PCB 402 may include one or more strings of LEDs 416, with multiple LEDs 416 in a string. For example, a string may include eight LEDs 416 and each PCB 402 may include two strings for a total of sixteen LEDs 416. In this configuration, a light panel 204 having eight PCBs 402 would include ninety-six LEDs 416. It is understood that although the PCBs 402 are shown as being substantially identical, they may be different in terms of size, shape, and other factors for a single light panel 204.

In the present example, the LEDs 416 are surface mounted, but it is understood that the LEDs 416 may be coupled to the panel 204 using through hole or another coupling process. The surface mounted configuration may ensure that a maximum surface area of each LED 416 is in contact with the PCB 402, which is in turn in contact with the back panel 202 responsible for heat dissipation. Each string of LEDs may receive a constant current with the current divided evenly among the LEDs 416.

Referring to FIGS. 5A, 5B, 5C and 5D, one embodiment of a single lens panel 500 of the optics panel 206 is illustrated. In the present example, the optics panel 206 may include multiple lens panels 500, although it is understood that any number of lens panels may be used based on design issues such as the number, arrangement, and orientation of the LEDs 416, the size of the surface 102, and/or other factors. As shown in the present embodiment with a substantially rectangular cross-section that is configured for use with the PCB 402 of FIG. 4, a single lens panel 500 includes a front surface 502, a back surface 504, a top side 506, a bottom side 508, a right side 510, and a left side 512. The sides 506, 508, 510, and 512 may form a cavity into which the PCB 402 may fit, thereby providing protection for the PCB 402 from environmental conditions such as moisture.

The lens panel 500 may include a beveled or angled top side 506 and/or bottom side 508 as illustrated in FIG. 5B. The beveling/angling may aid in preventing moisture from reaching the PCB 402 under the lens panel 500, as water will more readily flow from the area of the joint 320 (FIG. 3C) due to the angled surface than if the top side 506 was relatively flat.

The lens panel 500 may include multiple optical elements 514. A single optical element 514 may be provided for each LED 416, a single optical element 514 may be provided for multiple LEDs 416, and/or multiple optical elements 514 may be provided for a single LED 416. In some embodiments, the optical elements 514 may be provided by a single multi-layer optical element system provided by the lens panel 500.

In the present example, the optical elements 514 are configured so that the light emitted from each LED 416 is projected onto the entire surface 102 of the billboard 100. In other words, if all other LEDs 416 were switched off except for a single LED 416, the entire surface 102 would be illuminated at the level of illumination provided by the single LED 416. In one embodiment, the rectangular target area of the surface 102 would be evenly illuminated by the LED 416, while areas beyond the edges 112, 114, 116, and 118 would receive no illumination at all or at least a minimal amount of illumination from the LED 416. What is meant by “evenly” is that the illumination with a uniformity that achieves a 3:1 ratio of the average illumination to the minimum. Thus, by designing the lens in such a manner, when all LEDs are operating, the light form the collective thereof will illuminate the surface at the 3:1 ratio. When one or more LEDs fail, the overall illumination decreases, but the uniformity maintains the same uniformity. Also, as described hereinabove, the “surface” refers to the surface that is associated with a particular LED panel. It may be that an overall illuminated surface is segmented and multiple panels are provided, each associated with a particular segment.

FIG. 5C illustrates a detail of the lens assembly. Each of the diodes 416 is mounted on the board 408 at a minimum distance. Overlying the board and LEDs 416 is transparent lens substrate 520. This substrate 520 has a plurality of lens structures 522, each associated with one of the LEDs 416, such that each of the LEDs 416 has the light emitted therefrom directed outward towards the surface, each lens structure being substantially the same. The minimum distance is designed such that overlapping light from adjacent LEDs does not create interference patterns and result in dead spots on the surface. The lens structure 522 is designed to create the 3:1 uniformity and also, the lens structure is designed to “direct” the light from an edge of the surface to cover the entire surface. This is shown by the angle of the light rays in FIG. 5C. Also, the beveled edge 530 will basically surround the PCB 402, thus protecting it from moisture. The lens substrate 520 is secured with screws (not shown).

FIG. 5D illustrates a detail of the lens structure 522. This structure includes an interior surface 524 and an exterior surface 526 that shapes and directs the light in the correct pattern. This is an acrylic material. With such a design, the lighting assembly can be disposed at an edge of the surface to illuminate the entire surface.

In some embodiments, as shown in FIG. 1, two lighting assemblies 110 may be used. Each lighting assembly may be powered by a separate power supply (not shown), and may be configured to illuminate the entire surface 102. In such an embodiment, if one power supply fails, the remaining lighting assembly 110 will still illuminate the entire surface 102, although at a lesser intensity than when both lighting assemblies 110 are functioning. This provides evenly distributed illumination when both lighting assemblies 110 are functioning correctly, and continues to provide evenly distributed illumination when one lighting assembly 110 malfunctions. Accordingly, the entire surface 102 of the billboard 100 may be illuminated even when an entire lighting assembly 110 has malfunctioned and is providing no illumination at all due to the redundancy provided by configuration of the lighting assemblies 110.

Furthermore, in some embodiments as described above, each LED 416 of a single lighting assembly 110 may be configured via the optical elements 514 to illuminate the entire surface 102. In such embodiments, if one or more LEDs 416 or strings of LEDs fails, the remaining LEDs 416 will still illuminate the entire surface 102, although at a lesser intensity than when the failed LEDs 416 are functioning. This provides evenly distributed illumination when all LEDs 416 are functioning correctly, and continues to provide evenly distributed illumination when one or more LEDs are malfunctioning. Accordingly, the billboard 100 may be illuminated even when multiple LEDs 416 have malfunctioned and are providing no illumination at all due to the redundancy provided by configuration of the lighting assemblies 110.

It is understood that some embodiments may direct substantially all illumination from a lighting assembly 110 evenly across the surface 102 while some illumination is not evenly distributed. For example, substantially all LEDs 416 may be directed to each evenly illuminate the surface 102 with the exception of a relatively small number of LEDs 416. In such cases, the illumination provided by the remaining LED or LEDs 416 may be directed to one or more portions of the surface 102. If done properly, this may be accomplished while minimizing any noticeable unevenness in the overall illumination, even if one of the remaining LEDs 416 malfunctions. For example, the lighting assembly 110 may be configured to direct the illumination provided by one LED 416 to only the left half of the surface 102, while directing the illumination from another LED 416 to only the right half of the surface 102. The loss of one of these two LEDs may not noticeably impact the illumination of the surface 102. It is understood that such variations are within the scope of this disclosure.

In embodiments where the illumination is evenly distributed across the surface 102, it is understood that the optics panel 206 may be configured specifically for the light panel 204 and the surface 102. For example, assuming the surface 102 is forty-eight feet wide and sixteen feet high, the lens panel 500 of FIG. 5 may be specifically designed for use with the PCB 402 of FIG. 4. This design may be based on the particular layout of the PCB 402 (e.g., the number and arrangement of the LEDs 416), the amount of illumination provided by the LEDs 416, the size of the surface 102, the distance between the lens panel 500 and the surface 102, the angle at which the lens panel 500 is mounted relative to the surface 102 (e.g., FIGS. 1B-1D), and/or other factors. Accordingly, changes in any of these factors may entail a change in the design of the lens panel 500 in order to again evenly distribute the illumination provided by each LED 416 across the entire surface 102. It is understood that various standard configurations of the lighting assembly 110 may be developed for various billboard and/or other externally illuminated signs so that a particular configuration may be provided based on the parameters associated with a particular billboard and/or externally illuminated sign.

Referring to FIGS. 6A-6C, one embodiment of a lighting assembly 600 is illustrated that provides a more detailed embodiment of the lighting assembly 200 of FIG. 2. The lighting assembly 600 includes a back panel 602, a light panel formed by multiple LED assemblies (denoted by reference number 800 in FIG. 8A), and an optics panel formed by multiple lens panels 604. Accordingly, as described previously, the light panel 204 in the current example is represented by multiple LED assemblies 800 and the optics panel 206 is represented by multiple lens panels 604. In the present embodiment, the lighting assembly 600 includes four LED assemblies 800 and four lens panels 604.

Although various attachment mechanisms (e.g., threaded screws, bolts, and/or other fasteners) may be used to coupled the lens panels and LED assemblies to the back panel 602, the present embodiment uses multiple threaded fasteners 605 (e.g., screws) that extend through the lens panels and the LED assemblies and engage threaded holes in the back panel 602.

The lighting assembly 600 is also illustrated with a mounting plate 606 that couples to the back panel 602 and to an adjustable mounting bracket 608. The adjustable mounting bracket 608 may be used to couple the lighting assembly 600 to a portion of the billboard 100 (FIG. 1) and/or to another support member. A power supply enclosure 610 may be coupled to the mounting plate 606 and configured contain a power supply (not shown) capable of supplying power to LEDs of the LED assemblies 800. It is noted that separating the power supply from the back panel 602 may aid in heat dissipation by the back panel 602 as it does not have to dissipate heat from the power supply to the same extent as if the power supply was mounted directly to the back panel 602.

The location of the power supply may also be beneficial as snow not melted by the heat produced by the LED may be melted by heat produced by the power supply. This may aid in reducing snow buildup on the LEDs.

With additional reference to FIGS. 7A and 7B, one embodiment of the back panel of FIG. 602 is illustrated. A front surface 700 includes multiple protrusions 702 that may be configured to protect the light panels (not shown) against moisture as previously described. The front surface 700 may include additional protrusions 704.

A back surface 706 includes multiple fins 708 that form a heat sink to aid in the dissipation of heat from the back panel 602. In the present example, the fins 708 are substantially rectangular in shape. In the present example, the back panel 602 is extruded and the fins 708 run parallel to the top edge with a longitudinal axis of each fin 708 being substantially parallel to a longitudinal axis of the back panel 602. Forming the fins 708 in a vertical manner is possible, but may increase the cost of the back panel 602 due to the extrusion process. As shown, the fins 708 may be substantially perpendicular to the back surface 706, and/or may be angled. In the present example, the fins 708 are angled such that near the top of the back panel 702, the fins 708 are angled towards the top.

Because the fins 708 are parallel to the top edge, heat may be trapped due to its inability to rise vertically. Accordingly, holes 710 may be present in some or all of the fins 708 (marked but not actually visible in the side view of FIG. 7B) to provide paths for the heat to rise vertically in spite of the orientation of the fins 708. The holes 710 may create a chimney effect that increases air flow across the fins 708 and aids in the cooling process. In some embodiments, some or all of the fins 708 may be angled such that heat is not trapped.

The back surface 706 may also include a groove 712 that is configured to receive a tongue of the mounting plate 606 in a tongue-in-groove manner.

With additional reference to FIGS. 8A-8J, embodiments of a single LED assembly 800 and a single lens panel 604 that may be used with the lighting assembly 600 are illustrated. As shown, the single LED assembly 800 and the single optics panel 604 may be configured for use together.

Referring specifically to FIG. 8A, the LED assembly 800 includes a substrate 802 (e.g., a PCB) onto which are mounted multiple LEDs 804. In the present example, the LED assembly 800 includes two strings of eight LEDs 804 each for a total of sixteen LEDs 804. It is understood that this is merely an example, and there may be more or fewer LEDs 804 on the light panel 800, and the LEDs 804 may be arranged in many different ways on the substrate 802.

Referring also to FIGS. 8B-8J, the optics panel 604 may include optical elements 806 arranged on an upper surface 808 of the optics panel 604. The optics panel 604 may further include sides 810, 812, 814, and 816 that are configured to fit around the edge of the substrate 802 of the light panel 800. The bottom edge of each side 810, 812, 814, and 816 abuts the front surface 700 of the back panel 602 and may be sealed to the front surface 700 using a moisture resistant sealant.

As shown in FIGS. 8D-8H, a single optical element 806 may include multiple lens elements designed to distribute the illumination provided by a single LED 804 across a surface such as the surface 102 of FIG. 1. A first lens element 820 may be positioned proximate to the LED 804, and additional lens elements 822, 824, and 826 may be positioned above the lens element 820. Multiple optical elements 806 may be combined and formed as a single optics panel 604 that is configured to operate with the LED assembly 800.

Referring to FIG. 9, another embodiment of a lighting assembly 900 is illustrated that provides a more detailed embodiment of the lighting assembly 200 of FIG. 2. The lighting assembly 900 is similar to the lighting assembly 600 of FIG. 6, but includes six LED assemblies rather than the four six LED assemblies of the lighting assembly 600. It is understood that the lighting assembly 900 may require a larger power supply than the lighting assembly 600 (e.g., a one hundred and fifty watt power supply instead of a one hundred and twenty watt power supply).

Although the preferred embodiment has been described in detail, it should be understood that various changes, substitutions and alterations can be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

1. A lighting device comprising: a heat sink having fins on a first side and a mounting surface of a second side opposite the first side;a substrate attached to the mounting surface of the heat sink;a plurality of LEDs attached to the substrate; anda single transparent substrate overlying all LEDs attached to the substrate, the transparent substrate including a plurality of optical elements, wherein each optical element overlies an associated one of the LEDs.

2. The lighting device of claim 1, further comprising a power supply disposed at the first side of the heat sink.

3. The lighting device of claim 1, wherein the transparent substrate comprises an uppermost substrate, an outer surface of the transparent substrate forming an exposed surface of the lighting device.

4. The lighting device of claim 1, further comprising: a second substrate attached to the mounting surface of the heat sink and spaced from the substrate;a second plurality of LEDs attached to the second substrate; anda second transparent substrate overlying all LEDs attached to the second substrate, the second transparent substrate including a plurality of optical elements, wherein each optical element overlies an associated one of the LEDs of the second plurality of LEDs.

5. The lighting device of claim 4, further comprising: a third substrate attached to the mounting surface of the heat sink and spaced from the substrate and the second substrate;a third plurality of LEDs attached to the third substrate; anda third transparent substrate overlying all LEDs attached to the third substrate, the third transparent substrate including a plurality of optical elements, wherein each optical element overlies an associated one of the LEDs of the third plurality of LEDs.

6. The lighting device of claim 4, further comprising a power supply electrically connected to power the plurality of LEDs and the second plurality of LEDs, wherein the power supply is connected to power only LEDs attached to a substrate that is attached to the mounting surface of the heat sink.

7. The lighting device of claim 1, wherein the substrate has a length and a width that is smaller than the length and wherein the fins extending in a direction parallel to the length of the substrate.

8. The lighting device of claim 1, wherein at least one of the fins extends away from the first side of the heat sink in a direction that is not parallel to a plane of the first side of the substrate.

9. The lighting device of claim 1, wherein each optical element includes a first portion, a second portion, and a third portion; wherein, for each optical element, the second portion of the optical element intersects with the first portion of the optical element in a region between the first portion of the optical element and the second portion of the optical element;wherein, for each optical element, the first portion of the optical element and the second portion of the optical element are shaped so that at least one surface normal of the first portion of the optical element intersects with at least one surface normal of the second portion of the optical element; andwherein, for each optical element, the third portion is adjacent the first and second portions.

10. The lighting device of claim 1, wherein each optical element includes a first portion, a second portion and a third portion; wherein, for each optical element, the first portion comprises a first curved surface;wherein, for each optical element, the second portion comprises a second curved surface that intersects with the first curved surface at a region between the first portion and the second portion;wherein, for each optical element, the first portion and the second portion each have a peak relative to the substrate, the peak being spaced from the region between the first portion and the second portion; andwherein, for each optical element, the third portion extends beyond the region between the first portion and the second portion in a direction away from the associated LED.

11. The lighting device of claim 1, wherein each optical element includes a first portion and a second portion; wherein, for each optical element, the second portion of the optical element intersects with the first portion of the optical element in a region between the first portion of the optical element and the second portion of the optical element; andwherein, for each optical element, the first portion of the optical element and the second portion of the optical element are shaped so that at least one surface normal of the first portion of the optical element intersects with at least one surface normal of the second portion of the optical element.

12. The lighting device of claim 1, wherein the optical elements are configured so that light emitted from the LEDs during operation illuminates only a substantially rectangular area.

13. The lighting device of claim 12, wherein the optical elements are configured so that the light emitted from the LEDs illuminates only the substantially rectangular area with a uniformity that achieves at most a 3:1 ratio of the average illumination to the minimum illumination across the substantially rectangular area.

14. The lighting device of claim 13, wherein the optical elements are configured so that the light emitted from the LEDs illuminates only the substantially rectangular area with a uniformity that achieves at most a 3:1 ratio of the average illumination to the minimum illumination across the substantially rectangular area regardless of whether all or only some of the LEDs are functional.

15. The lighting device of claim 1, wherein the lighting device is configured to direct light toward a substantially rectangular region such that the light from the LEDs illuminates the substantially rectangular region with an illumination level and a uniformity; and wherein the optical elements are configured so that failure of one or more of the LEDs will cause the illumination level of light impinging the substantially rectangular region to decrease while the uniformity of light impinging the substantially rectangular region remains substantially the same.

16. The lighting device of claim 1, wherein the optical elements and the associated LEDs are spaced to avoid hot spots on a region of illumination when the lighting device is operating.

17. A lighting device comprising: a plurality of LEDs;means for removing heat from the plurality of LEDs when the LEDs are emitting light;means for attaching all LEDs of the plurality of LEDs to the means for removing heat;a single transparent substrate overlying all LEDs of the plurality of LEDs, the transparent substrate including a plurality of optical elements, wherein each optical element overlies an associated one of the LEDs; andmeans for providing power to LEDs when the LEDs are emitting light.

18. The lighting device of claim 17, wherein the plurality of optical elements comprises means for directing light toward a substantially rectangular region such that the light from the LEDs illuminates the substantially rectangular region with an illumination level and a uniformity so that failure of one or more of the LEDs will cause the illumination level of light impinging the substantially rectangular region to decrease while the uniformity of light impinging the substantially rectangular region remains substantially the same.

19. A lighting device comprising: a heat sink having fins on a first side and a mounting surface of a second side opposite the first side, the mounting surface including a plurality of threaded holes;a first substrate attached to the mounting surface of the heat sink, the first substrate having a length and a width that is smaller than the length;a first plurality of LEDs attached to the first substrate;a first transparent substrate overlying all LEDs attached to the first substrate by multiple threaded fasteners that extend through the first transparent substrate and the first substrate and engage the threaded holes of the mounting surface of the heat sink, the first transparent substrate including a first plurality of optical elements, wherein each optical element of the first plurality of optical elements overlies an associated one of the LEDs of the first plurality of LEDs and wherein the first transparent substrate comprises an uppermost substrate, an outer surface of the first transparent substrate forming a first exposed surface portion of the lighting device;a power supply electrically connected to power the first plurality of LEDs.

20. The lighting device of claim 19, further comprising: a second substrate attached to the mounting surface of the heat sink and spaced from the first substrate;a second plurality of LEDs attached to the second substrate; anda second transparent substrate overlying all LEDs attached to the second substrate, the second transparent substrate including a second plurality of optical elements, wherein each optical element of the second plurality of optical elements overlies an associated one of the LEDs of the second plurality of LEDs and wherein the second transparent substrate comprises an uppermost substrate, an outer surface of the first transparent substrate forming a second exposed surface portion of the lighting device;a third substrate attached to the mounting surface of the heat sink and spaced from the first substrate and the second substrate;a third plurality of LEDs attached to the third substrate; anda third transparent substrate overlying all LEDs attached to the third substrate, the third transparent substrate including a third plurality of optical elements, wherein each optical element of the third plurality of optical elements overlies an associated one of the LEDs of the third plurality of LEDs and wherein the third transparent substrate comprises an uppermost substrate, an outer surface of the third transparent substrate forming a third exposed surface portion of the lighting device;wherein the power supply electrically is connected to power the first plurality of LEDs, the second plurality of LEDs and the third plurality of LEDs.

21. The lighting device of claim 19, wherein the power supply is electrically connected to power only LEDs attached to a substrate that is attached to the mounting surface of the heat sink.

22. The lighting device of claim 19, wherein at least one of the fins extends away from the first side of the heat sink in a direction that is not parallel to a plane of the first side of the substrate.

23. The lighting device of claim 19, wherein the optical elements are configured so that light emitted from the LEDs during operation illuminates only a substantially rectangular area.

24. The lighting device of claim 23, wherein the optical elements are configured so that the light emitted from the LEDs illuminates only the substantially rectangular area with a uniformity that achieves at most a 3:1 ratio of the average illumination to the minimum illumination across the substantially rectangular area.

25. The lighting device of claim 24, wherein the optical elements are configured so that the light emitted from the LEDs illuminates only the substantially rectangular area with a uniformity that achieves at most a 3:1 ratio of the average illumination to the minimum illumination across the substantially rectangular area regardless of whether all or only some of the LEDs are functional.

26. The lighting device of claim 19, wherein the lighting device is configured to direct light toward a substantially rectangular region such that the light from the LEDs illuminates the substantially rectangular region with an illumination level and a uniformity; and wherein the optical elements are configured so that failure of one or more of the LEDs will cause the illumination level of light impinging the substantially rectangular region to decrease while the uniformity of light impinging the substantially rectangular region remains substantially the same.

27. A lighting system comprising: a first lighting device comprising: a first heat sink having fins on a first side and a mounting surface of a second side opposite the first side;a first substrate attached to the mounting surface of the first heat sink;a first plurality of LEDs attached to the first substrate; anda first transparent substrate that is a single substrate that overlies all LEDs attached to the first substrate, the first transparent substrate including a first plurality of optical elements, wherein each optical element of the first plurality of optical elements overlies an associated one of the LEDs of the first plurality of LEDs; anda second lighting device comprising: a second heat sink having fins on a first side and a mounting surface of a second side opposite the first side;a second substrate attached to the mounting surface of the second heat sink;a second plurality of LEDs attached to the second substrate; anda second transparent substrate that is a single substrate that overlies all LEDs attached to the second substrate, the second transparent substrate including a second plurality of optical elements, wherein each optical element of the second plurality of optical elements overlies an associated one of the LEDs of the second plurality of LEDs;wherein the first lighting device is configured to light a first substantially rectangular area; andwherein the second lighting device is configured to light a second substantially rectangular area that is adjacent but does not overlap the first substantially rectangular area.

28. The lighting system of claim 27, wherein the optical elements of the first transparent substrate are configured to light the first substantially rectangular area with a uniformity that achieves at most a 3:1 ratio of the average illumination to the minimum illumination across the first substantially rectangular area; and wherein the optical elements of the second transparent substrate are configured to light the second substantially rectangular area with a uniformity that achieves at most a 3:1 ratio of the average illumination to the minimum illumination across the second substantially rectangular area.

29. The lighting system of claim 27, wherein the first lighting device is configured to direct light toward the first substantially rectangular area such that the light from the first plurality of LEDs illuminates the first substantially rectangular area with an illumination level and a uniformity; and wherein the optical elements of the first transparent substrate are configured so that failure of one or more of the LEDs of the first plurality of LEDs will cause the illumination level of light impinging the first substantially rectangular area to decrease while the uniformity of light impinging the first substantially rectangular area remains substantially the same.

30. A billboard comprising: the lighting system of claim 27; anda display surface, wherein the first substantially rectangular area comprises a first portion of the display surface and the second substantially rectangular area comprises a second portion of the display surface.