Light sources

High quality light sources are required for characterisation of the CCD detectors. For making flat field exposures and measureing quantum efficiency, a continuum source of relatively high intensity is required, covering the entire sensitivity band of the CCD, from 1100nm to 300nm.
A halogen light bulb has proven suitable for this. We prefer the No. 64614 12V, 75W bulb from Osram, designed for UV-curing of epoxies. With a UV-enhancing, IR transmitting reflector, it has a high UV flux without excessive heat load on our filters. The bulb must be cooled by a fan. It is driven by a current source, typicially delivering 2.5-3A for red/NIR exposures and up to 6A for UV exposures.

The UV-optimised halogen light bulb.

The light bulb intensity typically drifts by 1% over an hour, making it less suitable for e.g. sub-percent linearity measurements. For this purpose, we are using flourescent Tritium driven light sources. Even these are not completely stable, a decay of 6%/year of the Tritium has to be taken into account for long term measurements, and there is a temperature dependency of -0.3%/K.

Flourescent Tritium driven tablets in exterior lighting. Three are unmounted, while two are in adapters for thest setups, shielded by black tape to give the desired light output.

The flourescent tablets in darkness. Although only the red ones are clearly seen here, also green and blue sources are available.

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Last updated September 11, 2001