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:
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
The heat sink 12 may be defined by an elongated strip, as shown in
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
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
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
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
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
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
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 3M adhesive tape, as shown in
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
In the embodiment of
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
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
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
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.
Number | Date | Country | Kind |
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61/086837 | Aug 2008 | US | national |
This application claims the benefit of application Ser. No. 61/086,837 filed Aug. 7, 2008.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/US09/31417 | 1/20/2009 | WO | 00 | 2/4/2011 |