Applicability of UV and Blue High-Flux Light Emitting Diodes as In-Flight Radiometric Sources for CLARREO

Traditional incandescent on-board calibration sources do not provide the stability required for an on-board absolute calibration reference source for a mission like CLARREO where the allowable error due to calibration sources is very small (< 0.15% per decade). Commercial-off-the-shelf (COTS) light emitting diodes (LEDs) are appealing to use as calibration sources due to their potentially known spectral content, low power, and small packaging. However, these COTS devices are not designed for vacuum, radiation or temperature extremes and open literature searches do not yield extensive data for these devices. A targeted study at NGAS is investigating the inherent stability of COTS LEDs and their suitability for use as calibration sources in a space environment. A laboratory experiment has been conducted which applies temperature control, spectral characterization, and absolute radiometry via trap detector technology that is NIST-traceable to 1%. Initial results of turn-on to turn-on repeatability testing indicate relative output stability to less than ±0.5% and the continuous on-stability over a 45 min period to be ± 0.1%. The results demonstrated a cumulative measurement system limit which includes the errors associated with the power stability, temperature stability, precision of the detector outputs and the stability of the LED. We show that LED COTS devices, developed for use as calibration sources, may prove to be valuable components in the CLARREO calibration suite.