Our team has developed and tested a solid-state solar simulating lamp for use with space simulation vacuum chambers. Unlike traditional lamps, our system uses solid-state light-emitting diodes (LEDs) to generate the light. The emission wavelengths of the LEDs can be selected and controlled so that their combined output better approximates the profile of the solar spectrum.

Though our system can accommodate visual or infrared LEDs, we focused our efforts on generating ultraviolet (UV) light in the 265-400 nanometer (nm) range. Compared to deuterium lamps, the LEDs are advantageous because they can be selected and controlled such that the output profile of the lamp better approximates the irradiance of the sun. Deuterium lamps are most intense at 200 nm with their intensity decreasing by more than 90% as the spectrum approaches 400 nm. Light from the sun is of relatively low intensity in the 200-250 nm range, but its intensity increases by more than 2000% from 250 nm to 400 nm.

The modular design of our lamp (Figure 1) allows it to individually control the current to each of 80 strings of LEDs, totaling to 904 individual UV LEDs in a compact, circular pattern designed to shine through an 11.5-inch-diameter chamber window. The light from each LED is collimated using a 6-millimeter-diameter silica ball lens, and the array has a combined nominal optical power output of 90 watts (W). Because UV LEDs are relatively inefficient, creating the 90W of optical power requires 1800W of electrical power. The waste heat from the LEDs is managed by a liquid-cooled plate and external chiller.

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