Patent Application
20120306351
This invention relates generally to the field of LED lighting fixtures and, more particularly, to the field of LED-based light sources for use in fixtures with specific light-distribution requirements.
In recent years, the use of light-emitting diodes (LEDs) for various common lighting purposes has increased, and this trend has accelerated as advances have been made in LEDs, LED arrays, and specific components. 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 lighting 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. One example is fixtures for roadway lighting, an application in which the fixtures are generally placed along roadway edges while light distribution is desired along a significant portion of roadway length and, of course, on the roadway itself—generally to the exclusion of significant light off the roadway. 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.
The present invention is an LED light source which satisfies all of the above-noted objects and purposes. The LED light source of this invention comprises a submount including an LED-populated area which has an aspect ratio greater than 1, an array of LEDs on the LED-populated area, and a lens on the submount over the LED-populated area.
As used herein, the term “LED-populated area” means an area (i.e., an area on the submount) the outer boundaries of which include the outermost edges of the outermost LEDs (of the LED array) in any direction. As used herein, the term “aspect ratio” means the ratio of the maximum cross-dimension of the LED-populated area to the maximum of the cross-dimensions orthogonal thereto.
In certain embodiments of the inventive LED light source, the spacing and arrangement of the LEDs of the array are such that the total LED area is at least about one-third of the LED-populated area. In some embodiments, the spacing and arrangement of the LEDs of the array are such that the total LED area is at least about two-thirds of the LED-populated area, and in some of these embodiments, the spacing and arrangement of the LEDs of the array are such that the total LED area is about 90% of the LED-populated area.
As used herein, the term “total LED area” means the sum of the submount areas immediately beneath each of the LEDs of the LED array.
In certain other embodiments, the spacing between LEDs of the array is no more than about 1 millimeter (mm), and in some of these embodiments, the spacing between LEDs is no more than about 0.5 mm, and sometimes no more than about 0.1 mm. And in certain other embodiments, the spacing is no more than about 0.075 mm, and even no more than about 0.05 mm.
In other embodiments of this invention, the aspect ratio of the LED populated area is at least about 1.25. In some of these embodiments, the aspect ratio is at least about 1.5, and in other embodiments, aspect ratio is at least about 2.
The LED-populated area in some embodiments is rectangular. For example, one such embodiment includes a rectangular array of LED's including at least eight LEDs positioned in two rows of four LEDs in each row. In another, the array includes forty-eight LEDs positioned in four rows of twelve LEDs in each row. In certain other embodiments, the LED-populated area is asymmetric.
“Asymmetric,” as used herein with respect to LED-populated areas, when unmodified by any further limiting description, refers to an area the boundary of which is a geometric shape having no more than one axis around which there is bilateral symmetry. Therefore, it should be understood that LED-populated areas which are rectangular are not asymmetric, given that they have two axes around which there is bilateral symmetry.
In certain embodiments of this invention, the LED light source is configured to refract LED-emitted light toward a preferential direction. The LED array defines an emitter axis, and in certain embodiments the lens has an outer surface and a centerline which is offset from the emitter axis toward the preferential direction. In some of these embodiments, the lens is shaped for refraction of LED-emitted light toward the preferential direction. The lens may be asymmetric.
As used herein, the term “emitter axis” means the line orthogonal to the plane defined by the LED-populated area and passing through the geometric center of the minimum-area rectangle bounding the LED-populated area, i.e., the center of the rectangle of minimum area which includes all of the LED-populated area.
The term “asymmetric,” as used herein with respect to lenses, when unmodified by any further limiting description, refers to a lens shape which is not rotationally symmetric about any axis perpendicular to its base plane. Types of asymmetric lenses include without limitation bilaterally symmetric lenses.
In some embodiments in which the light source is configured to refract LED-emitted light toward a preferential direction, the LED-populated area has major and minor orthogonal cross-dimensions and the preferential direction is along the minor cross-dimension, thereby to provide an illumination pattern which is offset toward the preferential direction with respect to the emitter axis.
In certain embodiments of this invention, the lens is overmolded on the submount. The submount may comprise ceramic material, and may be aluminum nitride. The submount has front and back sides, and the LED-populated area may be on the front side, with electrodes on the back side for connection purposes.
The light source of this invention may also be described as comprising (a) a submount including an LED-populated area with an array of light-emitting diodes (LEDs) thereon, the LED-populated area having first and second maximum cross-dimensions orthogonal to one another where the first cross-dimension is greater than the second cross-dimension, and (b) a lens on the submount over the LED-populated area.
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.
In
Contact pad metallization layers include a titanium layer, a copper layer and a silver layer on a portion of aluminum nitride ceramic layer 21. The silver layer may be the outmost layer on both front and back sides. The copper layer is an intermediate layer between silver and titanium. And, the titanium layer may be the innermost layer applied directly to ceramic 21. Approximate layer thicknesses may be as follows: aluminum ceramic layer 309 is or about 0.50 mm; titanium layer 315 is or about 0.06 microns; copper layer 317 is or about 50 microns; and silver layer 319 is or about 3.5 microns.
Therefore, each of LEDs 13p is connected to a positive power terminal at contact pad 211p, such positive electrical connection being first made at mounting pad 231p and connected to contact pad 211p through vias 25. Electric current then flows through each LED 13p and through wirebond connections 27 to intermediate contact pad 211i. The electric current continues to flow through each LED 13i which is bonded at its anode side to intermediate contact pad 211i. Electric current then continues to flow through negative contact 2111 and then to negative mounting pad 231n which is connected to negative contact pad 211n through vias 25.
In essence, the connectivity of LED array 12a is four serial pairs of LEDs 13 wired in parallel to each other pair. Positive contact 211p is connected to the positive terminal of a DC driver circuit (not shown) and negative contact pad 211n is connected to the negative terminal of such driver circuit.
The double wirebond connection on each LED 13 provides electrical redundancy for each LED 13 to minimize total failure of any of LEDs 13, i.e. that if one wirebond fails the second wirebond would provide the necessary electrical connection.
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 is a continuation-in-part of patent application Ser. No. 13/021,496, filed Feb. 4, 2011, currently pending. The contents of the parent application are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13021496 | Feb 2011 | US |
| Child | 13441558 | US |
