Controlling Light

Operational supplies are frequently used to regulate the intensity of heavy-duty light sources such as xenon or arc lamps. The uniform illumination of a monochronometer is a typical objective. Light sensors typically provide the regulating feedback. These sensors include photomultiplier tubes and photovoltaic or photoresistive semiconductors. Photovoltaic silicon photocells are the most convenient sensors. Their output, however, usually requires some voltage amplification before use as a command signal. A small dc amplifier is generally