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Projection Displays with High Power LEDs

R. Gale, H. Temkin, and J. Berg

Schematic diagram of a projection display system based on arrays of digital mirrors known as DMD.
Projection displays based on large arrays of digital mirrors offer high image brightness and resolution, as well as excellent color fidelity. The digital micromirrors themselves are exceptionally robust, reliable, and energy efficient. In contrast, high brightness lamps used in projection systems delivering well over 100 lumens on a screen are not efficient or reliable and present difficult thermal management problems. In this context, rapid development of high power light emitting diodes based on InGaN presents a possibility of replacing conventional lamps and simplifying the image formation process, an interesting challenge. Commercially available green (520 nm) and blue (480 nm) LEDs are now available with power outputs in the 100 mW range. However, the emission pattern of these devices and their thermal characteristics are poorly matched to the needs of projection systems.
Schematic diagram of a projection display system based on arrays of digital mirrors known as DMD.

 

Our research is focused first on understanding the limitations of current LED technology, the manufacturers at the leading edge of development, and the rate of advance. While evaluating currently available products, we are developing the optical systems required to couple the the light efficiently into the continuously evolving DLP™ systems. We are also evaluating reliabilty and lifetime issues in sequential pulsed operation, and some of the advantages that accrue from the rapid switching capability of LED illuminators. We have developed a detailed thermal model of high power LEDs and are currrently verifying thermal management of multiple LEDs flip-chip mounted on a common carrier.
Experimental projection system. Foreground: Green and blue LEDs illuminating a color combining prism; Background: the DMD chip and projection optics.
Experimental projection system. Foreground: Green and blue LEDs illuminating a color combining prism; Background: the DMD chip and projection optics.

Research Support: Texas Instruments