Illumination – Light fiber – rod – or pipe – Light emitting diode
Reexamination Certificate
2000-02-11
2001-11-20
O'Shea, Sandra (Department: 2875)
Illumination
Light fiber, rod, or pipe
Light emitting diode
C362S243000, C362S800000
Reexamination Certificate
active
06318886
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of The Invention
The present invention relates to the generation of high intensity light and, particularly, to light sources comprised of an array of light emitting diodes and an associated reflector, specifically a reflector assembly which cooperates with an efficient heat sink. This invention is also directed to the exercise of control over the aforementioned light sources so as to achieve high output light flux and long service life. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
2. Description of The Prior Art
The present invention relates to the use of arrays of light emitting diodes (LED's) to generate light which, when appropriately directed, is of relatively high intensity. When the LED's of such arrays are energized simultaneously and intermittently, the potential for employment of the resulting bursts of light for warning purposes is presented. In the prior art, however, the application of LED's arrays to uses such as, for example, emergency vehicle warning lights has been precluded by the inherent operating characteristics of the LED's themselves.
An LED, being a solid state electronic device, is susceptible to thermal damage. The possibility of damage resulting from overheating is, of course, increased when the devices are closely spaced in an array so as to present, to a viewer, the illusion of a single source of light. The requisite heat sinking, i.e., the transfer of heat away from the LED's of a closely spaced array, has not previously been accomplished in a manner which is economical and, when considered from both the thermal and volumetric view points, efficient.
The use of an array of closely spaced high output LED's to generate a high intensity light beam has also been impeded by the lack of a means for combining the light from all of the devices of the array into a single focused light beam in an optically efficient manner. Restated, the inherent spacial radiation pattern of an LED capable of producing a high luminous flux is such that the production of a beam of light from an array of such LED devices can be achieved only through appropriate focusing. Optics capable of accomplishing such focusing without significant attenuation have not previously been available.
A further impediment to the use of LED arrays to generate focused high intensity light resides in the electro-optic characteristics of the devices themselves. It is known that the magnitude of the light flux generated by an LED is directly proportional to the excitation current. However, it is also known that the service life of an LED is a function of the current which is caused to flow through the device over its life. Thus, a balance must be achieved between the excitation current, and thus the light output, and life expectancy. The achieving of such a balance becomes a particularly difficult task in the case of a vehicular application since the input voltage to the controller for the array will vary with the condition of the vehicle's battery and the rotational speed of the vehicle's alternator. In summary, prior controllers for LED arrays lacked the ability to provide and maintain a level of energization commensurate with a current flow which would achieve a preselected service life at an appropriate level of light flux.
SUMMARY OF THE INVENTION
The present invention overcomes the above briefly discussed and other deficiencies and disadvantages of the prior art and thereby allows the use of LED arrays to produce high intensity light, having a shaped spacial radiation pattern, while simultaneously ensuring a long service life.
The invention encompasses a unique reflector, optimally a single molded part, which defines an array of closely spaced frustoconical reflectors which receive individual LED's. In a preferred embodiment, the individual conical reflectors are arranged in rows and adjacent reflectors in each row are interconnected by means of generally obelisk shaped grooves which diverge in width from their bases to the side of the reflector assembly which faces in the direction in which the emitted light is to be transmitted.
In addition, the invention encompasses a unique technique for heat sinking an array of LEDs to provide a product which is both thermally and volumetrically efficient. The heat sink structure is multilayer and includes a printed circuit board, plated with copper on its opposed sides, with an array of copper plated through-holes which efficiently transfer heat from a first side of the PC board, which is bonded to the LEDs via an adhesive which has a high thermal conductivity, to the second side of the PC board. The layer of copper on the second side of the PC board is thermally coupled to a base, characterized by having a high thermal conductivity, via a low thermal resistance intermediate. This low thermal resistance intermediate may be defined by a thermally conductive encapsulate. The above-discussed reflector may be mounted on the multilayer heat sink structure.
The present invention further encompasses control circuitry which achieves and maintains a preselected average LED energization current, less than the rated peak current of the diodes, commensurate with a desired output light flux. This average energizing current is selected to take into account the characteristic light output versus time curve of the LED. A controller in accordance with the present invention also, in a preferred embodiment, compensates for variations in input, i.e., supply voltage. In one reduction to practice of the invention, the controller comprised a microprocessor operating as a current controlled pulse width modulator. In a preferred second embodiment, the controller was a step-down switching regulator.
In accordance with a third control circuit embodiment, which may be employed as an enhancement to the other embodiments, the controller varied the voltage applied to the LED's as a function of the temperature of the reflector.
REFERENCES:
patent: 5119174 (1992-06-01), Chen
Sousa David J.
Stopa James L.
Alix Yale & Ristas, LLP
O'Shea Sandra
Ward John Anthony
Whelen Engineering Company
LandOfFree
High flux led assembly does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with High flux led assembly, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and High flux led assembly will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2610450