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.