Increasing the output performance of LED-powered projectors is within our grasp. When the first LED-powered projectors were commercialized, they generated interest because of new properties and features such as permanent lamps, superior battery operation, higher color gamut and fanless cooling. However, these first units delivered only 10 to 15 real lumens, a brightness level that allowed only paper-size projections. Since then, product development has combined technologies to increase brightness.

Chip performance increases when higher-reflective internal mirrors are combined with thinner epitaxial layers, causing less internal photon reabsorption as light travels through the chip. A textured surface recently developed by Osram Opto Semiconductors GmbH of Regensburg, Germany, negates the prior limitations of total internal reflection by scattering reflected light back into the chip. By the time light is reflected back to the top surface at the internal mirror, it typically can escape the die. Yet, by increasing the current spreading capability of the epitaxial layers, the efficiency of the LED at higher currents does not drop as dramatically as that of conventional structures. By optimization of the contact geometries and of the thermal resistance of the dies, the thermally induced rollover of InGaAlP LEDs is enhanced from about 1.5 A/mm² to far beyond 3 A/m²...

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