Individual light shields

This application is a National Stage of International Application No. PCT/US2009/031417, filed Jan. 20, 2009. This application claims the benefit of U.S. Provisional Application No. 61/086,837, filed on Aug. 7, 2008. The entire disclosure of the above application is incorporated herein by reference.

1. Field of the Invention

The subject invention relates to a light emitting assembly of the type including light emitting diodes (L.E.D.s), and more particularly, efficient and full cutoff of light emissions.

2. Description of the Prior Art

Municipal or street light assemblies often generate spurious or scattered light emissions, which wastes usable energy. The scattered light also creates haze in the atmosphere, which obscures celestial objects and interferes with astronomical observations. Increased awareness of light pollution has created a demand for light assemblies achieving “full cutoff” or the “dark skies compliant” in the municipal and commercial lighting fields. Light assemblies meeting this criteria restrict or eliminate all light emissions above the horizon to reduce interference with astronomical observations. Full cutoff light assemblies also improve drivers' visual acuity by increasing contrast and reducing glare. In other words, light emitted by the light assemblies is directed onto the street rather than into drivers' eyes.

The U.S. Illumination Engineering Society has developed specifications for such a “full cutoff” designation. To meet the specification, the amount of light above eighty-five (85) degrees, i.e. upward light, emitting from the light assembly must be less than 1.5% of the total light flux of the light assembly, measured in lumens. Such a rigorous specification is difficult to achieve with conventional high intensity discharge (HID) single point light sources such as mercury, metal halide, or high pressure sodium lamps, due to geometric limitations. Specifically, the requirements for wide, non-scattered and uniform illumination, and the need to cut off light 5 degrees below the horizon, are difficult to reconcile in practical light assemblies, which typically include prismatic lenses that scatter light, unless the prismatic lenses are replaced with a relatively sophisticated reflector and aperture. An example of such an assembly is disclosed in the U.S. Pat. No. 7,244,050 Summerford et. al. The Summerford '050 patent discloses an HID light assembly including two sophisticated reflectors within a single light shield for achieving full cutoff.

In addition to achieving efficient and full cutoff light emissions, municipalities and commercial entities desire to replace HID street lamps with properly designed L.E.D. light assemblies. An example of such an assembly is disclosed in the U.S. Pat. No. 5,857,767 to the present inventor, Peter A. Hochstein, which is directed to effective thermal management. The Hochstein '767 patent discloses a light assembly including plurality of light emitting diodes disposed on a heat sink including a plurality of fins designed to enhance convective cooling. Proven metrics indicate that at least a fifty percent (50%) energy savings is possible due to the far greater service life that L.E.D. light assemblies offer.

At this time, and in the foreseeable future, L.E.D. light assemblies that are suitable replacements for conventional HID light sources, such as the assembly disclosed in the Hochstein '767 patent, contain a large number of L.E.D.s. These light assemblies are driven in series and/or parallel circuits to optimize their efficiency and generally occupy a much larger light emitting area than the HID light assemblies they replace. For example, while a 400 Watt HID light assembly might occupy an effective radiating area of a few square centimeters, an equivalent L.E.D. light assembly would present a source of several hundred square centimeters.

Obviously, such a distributed source is much more difficult to model optically, and to date it has not lent itself to effective, sharp cutoff beam shaping. With such relatively large and distributed source L.E.D. light assemblies, the simple expedient of using a single perimeter light shield to block high angle light, like those used for HID lamps, will not work. Each L.E.D. light source represents a unique geometry to the light shield. If a single light shield is used for a large number of L.E.D.s, light emitting from the L.E.D.s is scattered in undesired directions. If the entire light assembly is canted with respect to the horizon, the single light shield will be even more ineffective in controlling undesired scattered light. However, such canting or angular aiming of the entire light assembly is often required in order to properly cover the roadway surface with even illumination.

There remains a great need for an L.E.D. light assembly which achieves the full cutoff designation and prevents undesired scattered light to improve energy efficiency.

The subject invention provides for such a light assembly including a plurality of light emitting diodes disposed on a mounting surface. A light shield supported by the mounting surface is disposed over each of the light emitting diodes for directing light emitting from the light emitting diodes in a desired predetermined direction. The light shields are serially aligned along the mounting surface in the predetermined direction with an exterior surface of one light shield being exposed to light emitting from an adjacent light shield. The exterior surface of the light shields exposed to light emitting from the adjacent light shield is non-reflective for absorbing light emitting from the adjacent light shield.

The present invention allows L.E.D. light assemblies of any size to easily meet the U.S. Illumination Engineering Society's specifications for full cutoff designation. From an optical design standpoint, each L.E.D. source is considered as a single point source of light which may be optimally shielded by an individual light shield. The sharpness of the cutoff that can be achieved with the multiple light shield geometry is exemplary.

Further, the exterior surfaces of each light shield are painted flat black to absorb light emitting from an adjacent light shield. This prevents the undesired scattering of light which typically occurs when multiple light shields are disposed in close proximity. The interior surface of each light shield preferably comprises a reflective material, so light that might otherwise be lost to the light shield is redirected in the desired direction, such as a roadway surface. Proven metrics indicate that up to 20% more useful light is available with the arrangement of the subject invention.

Other advantages of the present invention will be readily appreciated, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIG. 1 is perspective view of a preferred embodiment of the subject invention wherein the individual light shields comprise a triangular shape;

FIG. 2 is a perspective view of a preferred embodiment of the subject invention wherein the mounting surface has an angle other than ninety degrees relative to the parallel fins;

FIG. 3 is a plan (frontal) view of a second embodiment of the subject invention wherein each light shield is disposed along and parallel to a row of the light emitting diodes; and

FIG. 4 is a fragmentary perspective view of a preferred embodiment of the subject invention showing one light emitting diode and the accompanying individual light shield comprising a triangular shape; and

FIG. 5 is a fragmentary cross sectional view taken along line 5 - 5 of FIG. 4 .

Referring to the Figures, alight emitting assembly 10 is generally shown. The light assembly 10 preferably comprises a heat sink 12 of thermally conductive material presenting a mounting surface 14 and a heat transfer surface 16 facing in the opposite direction from the mounting surface 14 , as shown in FIGS. 1 and 2 . The heat sink 12 is typically made of metal, such as a homogeneous aluminum or an aluminum alloy.

The heat sink 12 may be defined by an elongated strip, as shown in FIGS. 1 and 2 . As shown in FIG. 2 , a plurality of the elongated strips are disposed in spaced and parallel relationship to one another to present side edges defining an elongated slot 18 therebetween extending continuously alone adjacent side edges of the elongated strips to separate and render adjacent elongated strips independent of one another. The elongated slots 18 enhance the convective cooling of the assembly 10 by allowing ambient air to pass by each of the elongated strips.

In an alternative embodiment, the heat sink 12 may comprise a generally triangular shape extending from a wide top end 20 to a narrow bottom end 22 , as shown in FIG. 3 . The heat sink 12 comprising a generally triangular shape is typically disposed in a globe lamp defined by a spherical shape, which naturally has a diameter being larger in a middle area and tapering towards a bottom area of the lamp. Four of the heat sinks 12 comprising a generally triangular shape can be disposed in a bottom hemisphere of the globe lamp and tipped downwards at an angle of approximately thirty (30) degrees, so that the wide top ends 20 of the heat sinks 12 efficiently fill the larger middle area and the narrow bottom ends 22 efficiently fill the smaller bottom area of the lamp. Alternatively, the heat sinks 12 comprising a generally triangular shape can be disposed in a lantern defined by a square shape, which has a width being larger at a top area and tapering towards a bottom area of the lantern. The wide top ends 20 of the heat sinks 12 efficiently fill the larger top area and the narrow bottom ends 22 efficiently fill the smaller bottom area of the lantern.

The heat sink 12 includes a plurality of fins 24 extending transversely from the heat transfer surface 16 and disposed in spaced and parallel relationship to one another for transferring heat away from the heat sink 12 to surrounding ambient air, as shown in FIGS. 1 and 2 . In the embodiment wherein the heat sink 12 comprises the plurality elongated strips, the fins 24 extend continuously between ends of each of the elongated strips to present a void space 26 between adjacent fins 24 and open at the ends for exposing the void space 26 between the adjacent fins 24 to air. The heat transfer surface 16 of the elongated strips may be disposed perpendicular to the parallel fins 24 thereof, or at an angle other than ninety degrees relative to the parallel fins 24 thereof, as shown in FIGS. 1 and 2 . In the embodiment wherein the heat sink 12 comprises the generally triangular shape, the fins 24 may extend continuously between the wide top end 20 and narrow bottom end 22 .

The light emitting assembly 10 includes a plurality of light emitting diodes 28 disposed on the mounting surface 14 . The light emitting diodes 28 on the mounting surface 14 of the heat sink 12 are serially aligned in a row, as shown in FIG. 1 , or in a plurality of rows spaced and parallel to one another, as shown in FIG. 3 , and electrically interconnected in series with one another. In the embodiment wherein the heat sink 12 comprises the plurality of elongated strips, the light emitting diodes 28 on the mounting surface 14 of each elongated strip are typically electrically interconnected in parallel with the light emitting diodes 28 on the other elongated strips, but the elongated strips may be electrically interconnected in series with the light emitting diodes 28 on the other elongated strips if a high voltage power supply is used. In the embodiment wherein the heat sink 12 comprises a generally triangular shape, the light emitting diodes 28 are aligned in rows decreasing in length from the wide top end 20 to the narrow bottom end 22 of the heat sink 12 .

The light assembly 10 preferably includes an insulation coating 30 of electrically insulating material disposed over the mounting surface 14 of each heat sink 12 , as shown in FIG. 5 . The insulation coating 30 is less than one thousand microns thick, but preferably about 50 microns thick. The insulation coating 30 may be continuous and cover the entire mounting surface 14 , or it may be disposed in circuitous tracks separated from one another by the bare mounting surface 14 .

A plurality of circuit traces 32 are spaced from one another and disposed on the insulation coating 30 of the mounting surface 14 for preventing electrical conduction between the traces 32 and from each of the traces 32 to the mounting surface 14 . Each light emitting diode 28 spans the space between the ends of adjacent traces 32 , as shown in FIG. 4 . Each light emitting diode 28 has a positive lead 34 and a negative lead 36 , as shown in FIG. 4 , being in electrical engagement with the adjacent ones of the traces 32 to electrically interconnect the traces 32 and the light emitting diodes 28 . An electrically conductive adhesive secures the leads 34 , 36 to the circuit traces 32 . The electrical components of the light assembly 10 are typically connected with printed, foil or wire conductors, and the conductor feed-throughs should be sealed when the assembly 10 is used outdoors.

The light assembly 10 typically includes a protective and conformal coating 38 of electrically insulating material disposed over the mounting surface 14 , as shown in FIGS. 1 , 2 and 5 , to protect the them from physical damage, moisture, and other environmental elements. The conformal coating 38 may be disposed over the light emitting diodes 28 and corresponding electrical components, including the circuit traces 32 , light emitting diodes 28 and leads 34 , 36 , or any number of these components. The conformal coating 38 is typically a very durable two component, chemically catalyzed, urethane. The conformal coating 38 is preferably a translucent material and about 50 microns in thickness.

A light shield 40 , generally indicated, is disposed on the mounting surface 14 adjacent each light emitting diode 28 . The light shields 40 are typically disposed on the mounting surface 14 after the conformal coating 38 is applied, so that the conformal coating 38 prevents the light shields 40 from electrically shorting the light emitting diodes 28 and accompanying electrical components. The light shields 40 may be disposed over the mounting surface 14 of the heat sink 12 with a light shield adhesive 42 comprising an ultraviolet cured cyanoacrylate material or a 3 M adhesive tape, as shown in FIG. 4 .

The light shields 40 typically comprise a thermally stable opaque material. The light shields 40 are defined by sections 44 extending upwardly at a predetermined angle from the mounting surface 14 over at least one of the light emitting diodes 28 to a forward edge 46 defining a forward facing opening for directing the light out of the forward facing opening in a predetermined direction. For example, the light shields 40 can extend at the predetermined angle to direct light five degrees below the horizon and towards a roadway, to achieve the full cutoff designation. The sections 44 connect at a ridge 48 extending upwardly from the mounting surface 14 to a peak 50 . The distance between the light emitting diode 28 and the light shield 40 and the predetermined angle of the light shield 40 may be varied from light shield 40 to light shield 40 for directing light in various directions and angles.

In the embodiment of FIGS. 1 and 4 , the light shields 40 include a pair of sections 44 each defined by a triangular shape. The pair of sections 44 join at the ridge 48 extending upwardly from the mounting surface 14 to the peak 50 so that the forward facing opening comprises a triangular shape. One of the light shields 40 is be disposed adjacent each of the light emitting diodes 28 , as shown in FIG. 1

In the embodiment of FIG. 3 , each of the light shields 40 comprises three of the sections 44 . One of the three sections 44 is a central section 44 , disposed centrally and along and parallel to one of the rows of light emitting diodes 28 . A pair of the sections 44 are disposed at section ends of the one central section 44 and join the one central section 44 at the ridge 48 extending upwardly from the mounting surface 14 to the peak 50 so that the forward facing opening comprises a rectangular shape.

Each of the sections 44 of the light shields 40 include an exterior surface, typically facing away from the mounting surface 14 . Each of the sections 44 include and an interior surface, opposite the exterior surface, for reflecting the light from the at least one light emitting diode 28 disposed there under out of the forward facing opening in the predetermined direction. The light shields 40 are typically serially aligned along the mounting surface 14 in the predetermined direction to accumulate light so that the exterior surface of one light shield 40 is exposed to light emitting from an adjacent rearwardly spaced light shield 40 . For example, in the embodiment of FIG. 3 wherein the heat sink 12 comprises a generally triangular shape, the exterior surface of each of the light shields 40 face toward the wide bottom end of the mounting surface 14 to accumulate light in the predetermined direction.

The exterior surface is inherently non-reflective or by way of a non-reflective film 52 or coating disposed over the exterior surface of each light shield 40 and is exposed to light emitting from the adjacent rearwardly spaced light shield 40 for absorbing light emitting from the adjacent rearwardly spaced light shield 40 , as shown in FIG. 5 . The non-reflective film 52 prevents light from reflecting off the exterior surface of the light shields 40 , i.e., prevents undesired scattered light. The non-reflective film 52 typically comprises a flat black color painted onto the exterior surface.

The light shields 40 typically have an interior surface which is inherently reflective or by way of a specular or reflective material 54 disposed over the interior surface for reflecting light emitting from the light emitting diodes 28 disposed there under in the predetermined direction. The reflective material 54 is disposed over the interior surface, as shown in FIG. 5 . By including a reflective interior surface, light that might otherwise be absorbed and lost to the light shield 40 can be redirected in the predetermined direction. The interior surface with the reflective material 54 , combined with the non-reflective film 52 disposed over the exterior surface, gives rise to 20% more useful light, compared to L.E.D. light assemblies 10 without such an arrangement.

Obviously, many modifications and variations of the present invention are possible in light of the above teachings and may be practiced otherwise than as specifically described while within the scope of the appended claims. These antecedent recitations should be interpreted to cover any combination in which the inventive novelty exercises its utility. The use of the word “said” in the apparatus claims refers to an antecedent that is a positive recitation meant to be included in the coverage of the claims whereas the word “the” precedes a word not meant to be included in the coverage of the claims. In addition, the reference numerals in the claims are merely for convenience and are not to be read in any way as limiting.