The Exotech Incorporated Model 100 BX Hand-held Radiometer is a compact, lightweight, rugged and entirely self-contained, four channel instrument designed for use in the field environment. The unit can be internally powered by two 9-volt batteries or externally powered by a 12-18 volt power supply.  Measurements can be read one channel at a time by a built in analog meter or the four channels can be recorded simultaneously by analog output (single ended analog output 0-7.5 volt DC.) Each channel is measured by a silicon photodiode and high sensitivity DC amplifier [low noise, field-effect transistor (FET) input, operational amplifiers (Burr-Brown 3528BM).] An important feature of the radiometer is that each of the four independent channels has separate gain controls (1x, 5x, 25x and 125x).  The feature aids in measurement accuracy in cases where there is a large difference in radiance in the four spectral bands.