Patent Grant
9435526
This invention relates generally to the field of LED light fixtures and, more particularly, to the field of LED light fixtures for various high-luminance area lighting applications such as roadway lighting, factory lighting, parking lot lighting, commercial building lighting, and the like.
In recent years, the use of light-emitting diodes (LEDs) in development of light fixtures for various common lighting purposes has increased, and this trend has accelerated as advances have been made in the field. Indeed, lighting applications which previously had typically been served by fixtures using what are known as high-intensity discharge (HID) lamps are now being served by LED light fixtures. Such lighting applications include, among a good many others, roadway lighting, factory lighting, parking lot lighting, and commercial building lighting.
In many of such products, achieving high levels of illumination over large areas with specific light-distribution requirements is particularly important. And in such situations it is desirable to minimize the use of large complex reflectors and/or varying orientations of multiple light sources to achieve desired illumination patterns.
Lighting fixtures using LEDs as light sources for various applications present particularly challenging problems. Heat dissipation is one particular problem. To ensure LED longevity and excellent long-term light-output performance, it is important that heat transfer away from the LEDs be facilitated in order to minimize thermal damage which may occur to LEDs during operation. Another problem, particularly when fixture mounting locations vary, is keeping LEDs protected from water, especially in outdoor locations. Dealing with these sorts of performance-related problems may sometimes be particularly difficult and involve various subtleties. In the present invention, long and involved trial-and-error development efforts led to performance breakthroughs.
In short, there is a significant need in the lighting industry for improved lighting fixtures using LEDs—fixtures that address problems associated with heat dissipation and appropriate protection of LEDs and which are adaptable for a wide variety of mountings and situations. Furthermore, there is a need for an improved LED-based lighting fixtures with high light-output performance and that are easy and cost-effective to manufacture.
The present invention is improved lighting apparatus including a circuit board having a plurality of light sources spaced thereon. The light sources may be solid-state light sources such as light emitting diodes (LEDs). The circuit board includes a circuit-board middle area and a circuit-board peripheral area and has a thermal-engagement surface opposite the light sources. The lighting apparatus also includes a heat sink having a surface for receiving the circuit board. A securement structure secures the circuit board to the heat sink. The securement structure includes a rigid peripheral structure applying force along the circuit-board peripheral area toward the heat sink to increase thermal contact across the facing area of the thermal-engagement surface of the circuit board and the surface of the heat sink.
This arrangement facilitates removal of heat from the light sources during operation by increasing surface-to-surface contact between the thermal-engagement surface of the circuit board and the surface of the heat sink. This facilitates excellent, substantially uniform thermal communication from the circuit board to the heat sink, thereby increasing heat transfer from the LEDs to the heat sink during operation.
In some embodiments, the rigid peripheral structure is a one-piece frame. The rigid peripheral structure may have a pressing portion with a substantially planar pressing surface and a stiffening portion which maintains planarity of the pressing surface.
In certain embodiments, prior to securement at least one of the thermal-engagement surface of the circuit board and the heat sink surface has a convexity. In some of such embodiments, the convexity is two-dimensional, such as bowing. In some other embodiments, the convexity is three-dimensional.
In some of these embodiments, the thermal-engagement surface of the circuit board has the convexity such that, prior to securement, distances between the thermal-engagement surface of the circuit board and the surface of the heat sink are greater along the circuit-board peripheral area than along the circuit-board middle area. In such embodiments, securement reduces the convexity. In some of such embodiments, the thermal-engagement surface of the heat sink is substantially flat.
In alternative embodiments, the surface of the heat sink has the convexity such that (a) prior to securement, distances between the thermal-engagement surface and the heat-sink surface are greater along the circuit-board peripheral area than along the circuit-board middle area. In such embodiments, securement conforms the thermal-engagement surface of the circuit board to the convexity.
The lighting apparatus may also include an optical member over the circuit board. The optical member has a lens region and a peripheral region. The lens region includes a plurality of lens portions each over corresponding light sources. The optical member is one-piece of a substantially rigid material such as acrylic. The securement structure engages the peripheral region of the optical member which sandwiches the circuit board against the heat-sink surface. The rigid peripheral structure of the securement structure provides substantially even pressure on the one-piece optical member which in turn presses the circuit board substantially uniformly against the heat sink. This facilitates heat transfer from the LEDs to the heat sink during operation.
In some embodiments, the optical member has a circuit-board-adjacent surface which, prior to securement, has a convexity that is reduced by securement. The convexity may be two-dimensional such as bowing. In some other embodiments, the convexity is three-dimensional.
The term “two dimensional,” as used herein, means that a surface has two-dimensional convexity if lines along one coordinate direction of the surface are convex and lines along the perpendicular coordinate direction of the surface are straight. An example of forming a bowed (or two-dimensionally convex) surface is the simple bending of a flat sheet in one direction to form an elongate raised surface. The term “three-dimensional,” as used herein means that a surface has three-dimensional convexity if along any direction, lines along the surface are convex. An example of a three-dimensional convex surface is a segment of a ball.
In some embodiments, particularly where the heat sink is open to water/air flow, the peripheral region of the optical member extends beyond and encircles the perimeter of the circuit board. The peripheral region of the optical member sandwiches a gasket against the heat sink, thereby facilitating fluid-tight sealing of the circuit board.
The rigid peripheral structure of the securement structure may be over the peripheral region of the optical member.
In certain embodiments, the lens region of the optical member is free of engagement by the securement structure. This simplifies the structure of the lighting apparatus while (1) facilitating heat-transfer engagement of the circuit board with a heat sink as described below, (2) allowing appropriate sealing against moisture ingress and (3) permitting optical-member glow thereacross because the securement structure is located only at the peripheral region. In some embodiments, the rigid peripheral structure may be overmolded in the peripheral region of the optical member.
In certain embodiments, the rigid peripheral structure is a one-piece frame disposed along the peripheral region of the optical member. The one-piece frame may be a drawn sheet-metal piece. In some of such embodiments, the rigid peripheral structure has a pressing portion with a substantially planar pressing surface and a stiffening portion which maintains rigidity and planarity of the pressing surface.
In some of the embodiments with the rigid peripheral structure over the peripheral region of the optical member, the peripheral structure is pressed against the optical member by a set of fasteners. Each fastener includes a fastener head and a threaded shank which extends from the fastener head through the rigid peripheral structure and through the optical member into threaded engagement with the heat sink.
In some embodiments, the heat sink includes a base which has the surface to which the circuit board is thermally coupled. In some of such embodiments, the heat sink includes a set of mounting posts each extending from the base through the peripheral region of the optical member to a distal post-end which is open to receive one of the fasteners. The distal post-ends are positioned, i.e., the posts are of a particular length, such that the posts limit compression of the rigid peripheral structure against the optical member caused by the fasteners.
The heat sink may include a surrounding structure around the optical member and configured such that the peripheral region of the optical member is recessed with respect to the surrounding structure. In certain of such embodiments, the stiffening portion of the rigid peripheral structure extends outwardly from the pressing portion of the peripheral structure and engages the surrounding structure of the heat sink.
The heat sink also has heat-transfer surfaces extending from the base in a first direction away from the circuit board, e.g., extending upwardly if the surface of the heat sink to which the circuit board is coupled faces downwardly. The heat-transfer surfaces of the heat sink may be surfaces of a plurality of fins extending away from the base in the first direction. In such embodiments, the surrounding structure may include a peripheral ridge extending from the base in a second direction opposite the first direction to provide additional heat-dissipating surface along the base. In some of such embodiments, at least a section of the peripheral ridge has an outward surface which is a continuation of a heat-transfer surface of one of the fins, such fin being a side fin along one side of the base.
In certain embodiments, the heat sink has a first positioning feature and the circuit board includes a second positioning feature. The first and second positioning features are configured and arranged for locating the circuit board along the heat sink. The optical member may include a third positioning feature in mating engagement with at least the second positioning feature of the circuit board to accurately align the optical member over the light sources.
In some of such embodiments, the first positioning feature is a cavity open at the heat-sink surface, and the second positioning feature is an aperture through the circuit board. In such embodiments, the third positioning feature may be a protrusion extending from the optical member, through the aperture of the circuit board, and into the cavity of the heat sink, thereby simultaneously locating the circuit board along the heat sink and accurately aligning the optical member over the light sources.
In some embodiments, the securement structure may include a set of screws each extending through the circuit-board middle area into threaded engagement with the heat sink, although the coupling between the circuit board and the heat sink may be free of screws. In embodiments free of screws, the circuit board may be positioned on the heat sink using first, second and third positioning features such as those described above.
In embodiments in which the circuit-board-adjacent surface of the optical member has convexity prior to securement, reduction (e.g., elimination) of such convexity by virtue of force applied on the peripheral region of the optical member by the rigid peripheral structure of the securement structure causes pressing of the middle area of the circuit board toward the heat sink with the first, second and third positioning members properly aligned. This further facilitates thermal coupling across the facing area of the circuit-board thermal-engagement surface and the heat-sink surface.
In descriptions of this invention, including in the claims below, the terms “comprising,” “including” and “having” (each in their various forms) and the term “with” are each to be understood as being open-ended, rather than limiting, terms.
Such application of force along the peripheral area of the circuit board tends to minimize warping of the circuit board which would result in inadequate heat-transfer contact between the circuit board and the heat sink during operation. In attempts to minimize the negative effect of warping, several intermediate materials such as thermal gel, thermal pads and screen printing on the thermal-engagement surface of the circuit board have been used between the circuit board and the heat sink. None of these methods provided sufficient thermal coupling of the circuit board to the heat sink to permit driving of LEDs to their higher capacity. It has been found that force applied by rigid peripheral structure 41 along peripheral area 21 of circuit board 20 increased thermal contact between thermal-engagement surface 25 of circuit board 20 and surface 510 of heat sink 50 which facilitated sufficient heat transfer from LEDs to allow safe LED operation at increased power levels over what was previously achieved. In fixtures utilizing single circuit board 20, the power level achieved was increased by about 100%. In fixtures where two circuit boards 20 were used side-by-side, the power level increase achieved was approximately 60%. Such substantial power level increases result in correspondingly greater light output of the fixtures without increases in number of LEDs or other changes in light sources.
In the alternative embodiment illustrated in
Heat sink 50 is shown to further include a surrounding structure 54 extending around optical member 30 such that flange portion 34 is recessed with respect to surrounding structure 54. In
In
In embodiments of
In an alternative embodiment schematically illustrated in
In another alternative embodiment schematically illustrated in
In yet another alternative embodiment schematically illustrated in
In still another alternative embodiment schematically illustrated in
In some embodiments each light source is an LED package which has one LED or an array of LEDs. A primary lens may be overmolded over the LED(s).
In fixtures of the type shown in
It should be understood that, for higher efficiency in achieving a preferential-side direction of light, LED light sources each may have a primary lens having its centerline offset from the emitter axis and/or be shaped for refraction of LED-emitted light toward a preferential side. Primary lenses may also be asymmetric. Some exemplary light sources are described in detail in patent application Ser. No. 13/441,558, filed on Apr. 6, 2012, and in patent application Ser. No. 13/441,620, filed on Apr. 6, 2012. Contents of both applications are incorporated herein by reference in their entirety.
While the principles of the invention have been shown and described in connection with specific embodiments, it is to be understood that such embodiments are by way of example and are not limiting.
This application claims the benefit of U.S. Provisional Application Ser. No. 61/745,552, filed Dec. 22, 2012 and U.S. Provisional Application Ser. No. 61/746,862, filed Dec. 28, 2012. The entirety of the contents of each of Application Ser. Nos. 61/745,552 and 61/746,862 are incorporated herein by reference.
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