Patent Application
20080273327
This is a continuation-in-part of patent application Ser. No. 11/744,807, filed on May 4, 2007 and entitled “Sealing and Thermal Accommodation Arrangement in LED Package/Secondary Lens Structure.”
The invention relates generally to the field of LED lighting systems and, more particularly, relates to configurations for LED modules in lighting fixtures.
In the field of lighting, many different types of light sources have been developed. Recently, LED light sources involving multi-LED arrays, each with a large number of LED packages, have been developed as a means of bringing the many advantages of LED lighting—LED efficiency and long life—into the general illumination field. In particular, such LED light fixtures have been developed for use in outdoor settings, including by way of example lighting for parking lots, roadways, display areas and other large areas.
LED fixtures in the prior art have certain shortcomings and disadvantages. Among these, there is a need for an improved arrangement for operation of LEDs having one lens positioned over another. Significant heat levels in such products can pose particular problems for lens-over-lens mounting and stability. One potential problem is that temperature changes may cause thermal expansion and related alignment problems.
Protection against various environmental factors is also rendered difficult for LED general illumination products which necessarily utilize a large number of LEDs—sometimes plural LED modules with each module having many LED packages thereon.
The product safety of lighting fixtures creates an additional area of difficulty, and such fixtures are most often required to comply within standards put forward by organizations such as Underwriters Laboratories Inc. (UL) in order to gain acceptance in the marketplace. One such set of standards deals with the accessibility of the electrically-active parts of a fixture during operation, and, more importantly, during periods of stress on the fixture such as in a fire situation during which some elements of the lighting fixture are compromised. The UL “finger test” mandates that a human finger of certain “standard” dimensions (defined in NMX-J-324-ANCE, UL1598, Dec. 30, 2004, FIG. 19.22.1, page 231) should not be able come in contact with any electrically-live parts of the fixture under such circumstances. The standards also establish certain material limitations on the enclosures of such products, all of which are dependent on the voltages and power levels within the fixtures.
Increased product safety can be costly to achieve, both in terms of the economic cost associated with providing safety as well as with the loss of lighting performance such as reduced optical efficiency. For example, placing a fixture behind a sheet of glass to provide increased safety can result in an optical efficiency loss of up to 10%.
For LED-based lighting fixtures, the cost of the power supply is an important part of the overall fixture cost. When a large number of LEDs are used to provide the necessary level of illumination, it is advantageous to use a single power supply providing higher voltages and higher power levels, which, in turn, requires more stringent safety standards. In particular, power supplies with a Class 2 power supply rating are limited to 100 watts at a maximum of 60 volts (30 volts if under wet conditions). LED-based lighting fixtures with a large number of LEDs can benefit (both by cost and efficiency) by using a Class 1 power supply, in which both the power and voltage limitations of a Class 2 power supply are exceeded. If power requirements for a lighting fixture are higher than the Class 2 limits, then multiple Class 2 power supplies are required (which can be costly) unless the more stringent safety standards which using a Class 1 supply brings about can be achieved.
As mentioned above, such more stringent requirements include satisfying the “finger test” under certain fire conditions during which it is possible that lighting module elements such as lenses made of polymeric materials may be removed. For example, in an LED package with a primary lens made of glass and a secondary lens made of polymeric material, ti is necessary to provide enclosure barriers over the entire electrical portion of the module (on which the LED packages are mounted) except over the primary lenses. It is assumed that under these circumstances, the polymeric secondary lenses will be destroyed in the fire, leaving the primary lenses exposed. Also for example, if a single polymeric lens is used in place of both the primary and secondary lenses, then the enclosure barriers must prevent “standard finger” access to the electrical elements under the assumption the single lens has been removed.
Thus there is a need for improved LED lighting fixtures which can better serve the requirements of general-illumination lighting fixtures and which can provide both the safety and cost-effectiveness which the marketplace requires and/or prefers.
It is an object of this invention to provide LED modules which overcome certain problems and shortcomings of the prior art including those referred to above.
An object of the invention is to provide an improved LED module which achieves the electrical product safety demanded by the marketplace.
Another object of the invention is to provide an improved LED module which achieves such safety in a cost-effective manner.
Still another object of the invention is to provide an improved LED module which achieves such electrical product safety under conditions during which no lens remains place over each LED package.
These and other objects of the invention will be apparent from the following descriptions and the drawings.
The invention is LED apparatus which provides electrical safety by satisfying a set of stringent safety standards for the enclosures in which such LED apparatus are encased, and doing so in a cost-effective manner. The LED apparatus of this invention includes a mounting board having a plurality of LED packages thereon with a lens member over each LED package and a safety barrier positioned over the mounting board. The barrier has sufficient thickness for enclosure of electrical elements on the mounting board and includes a plurality of openings each sized to permit light from an LED package to pass therethrough and through a light-transmission portion of the lens member over such LED package to prevent finger-contact of electrical elements on the mounting board when the light-transmission portion is not present.
In some embodiments of the LED apparatus, the barrier includes a metal layer, which in more preferred embodiments, the barrier also includes an insulating layer positioned between the mounting board and the metal layer. In some of these embodiments, the metal layer and the insulating layer form a laminate.
In other embodiments of the inventive apparatus, the safety barrier has a layer portion spaced from the mounting board, and in some of these embodiments, the safety barrier has at least one spacing structure supporting the layer portion on the mounting board.
In preferred embodiments of the invention, the LED apparatus further includes a resilient gasket member having apertures for each of the lens members, and the gasket member yieldingly constrains movement caused by thermal expansion during operation.
In more preferred embodiments of the inventive LED apparatus, the lens members each include a light-transmission portion and a flange thereabout. The gasket member is positioned against the flanges and includes an inner surface which faces and yieldingly abuts the flanges.
In highly-preferred embodiments of the invention, the LED apparatus further includes a cover which has openings aligned with the lens members and secures them over the LED packages, pressing the gasket member toward the safety barrier.
In other highly-preferred embodiments of the inventive LED apparatus, each of the lens members is a secondary lens and each LED package includes a primary lens in alignment with the secondary lens over such LED package. In some of these embodiments, the safety barrier is positioned between the flanges of the secondary lenses and the mounting board.
Further, this invention includes an LED light fixture which has a plurality of such inventive LED modules.
The term “LED package” as used herein means an assembly including (a) a base, (b) at least one LED (sometimes referred to as “die”) on the base, and (c), optionally, a primary lens over the die(s). One or more, typically several, LED packages are arranged on a mounting board in forming what is referred to as an “LED module.” One or more LED modules are used as the light source for various innovative lighting fixtures.
As shown in
Secondary lens 20 includes a lens portion (or “light-transmission portion”) 36 which is substantially transparent and a flange 38 portion thereabout. Lens portions 36 are adjacent to flange portions 38 as illustrated in
Secondary lenses 20, as illustrated in
Thermal expansion of primary lenses 16 results in abutment of lenses and displacement of secondary lenses 20. Resilient member 22 permits the displacement while holding secondary lenses 20 in place over primary lenses 16.
In certain embodiments a shield member 24, in the form of a layer, is positioned over the resilient member layer 22 as illustrated in
LED apparatus 10 includes a metal layer 30, preferably of aluminum. Layer 30 is positioned preferably immediately over the LED packages and includes a plurality of openings each sized to receive primary lens 16. Layer 30 is sandwiched between mounting board 12 and secondary lens 20 as seen in
LED apparatus 10 can include only one LED package 14 on a mounting board 12 with primary lens 16, a corresponding secondary lens 20 and a resilient member layer 22 against the secondary lens 20.
Insulating layer 30i serves to electrically isolate layer 30m from the electrical elements on mounting board 12. In some embodiments, these electrical elements may be isolated from layer 30m by a conformal coating on mounting board 12. Such conformal coating may be any of a number of available coatings, such as acrylic coating 1B73 manufactured by the HumiSeal Division of Chase Specialty Coatings of Pittsburgh, Pa.
Safety barrier 30 may also be made of a single layer of polymeric material having minimum thickness as set forth by the UL standards. Acceptable polymeric materials include BASF 130FR (polyethylene terephthalate with glass fiver reinforcement) supplied by the Engineering Plastics Division of BASF Corporation in Wyandotte, Mich. The layer has a minimum thickness of 0.028 inches. Other acceptable polymeric materials must satisfy certain detailed specifications related to material behavior such as hot-wire ignition, horizontal burning, and high-current arcing resistance, all of which are set forth in the UL standards referred to above.
LED module 46 may include safety barrier 30 which is positioned in several ways relative to mounting board 12 and secondary lenses 20. When LED packages 14 do not include optional primary lens 16, secondary lenses 20 are herein referred to as “lens members 50.”
In some forms of such highly preferred embodiments with the plurality of LED packages on the mounting board, it is preferred to use a Flame Resistant 4 (“FR4”) board formed by a conductor layer and an insulator layers. The conductor layer may be made of any suitable conductive material, preferably copper or aluminum. It is most highly preferred that such mounting board include, for each LED package thereon, a plurality of channels (“thermal vias”) extending through the mounting board at positions beneath the package, such channels having therein conductive material and/or an opening to facilitate transfer of heat through the board. The thermal vias provide an isolated thermal path for each LED package.
In the forms of the present invention using the FR4 mounting board with thermal vias, it is most highly preferred that each LED package 14 is constructed to have its cathode terminal electrically neutral from the thermal path, thus avoiding shortage of other LED packages 14 on the board.
A wide variety of materials are available for the various parts discussed and illustrated herein. While the principles of this apparatus have been described in connection with specific embodiments, it should b understood clearly that these descriptions are made only by way of example and are not intended to limit the scope of the invention.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11744807 | May 2007 | US |
| Child | 11774422 | US |
