e square of the distance between the lamp and the illuminated area. The placement of such lights is critical. They must be positioned so as to reduce annoying reflections and glare. Secondary lighting typically also serves as a backup should the primary lighting system fail (Schmickley, 1992, pp. 5-6).
Several different light sources may be employed for either primary and secondary lighting. Perhaps the most common of these is the incandescent lamp. Most such lamps contain a tungsten filament. Incandescent digital displays, for example, use subminiature lamps and lightpipes to display segments representative of either numbers or letters. Unfortunately, much of the energy emitted by these lights is in the red and infrared wavelength regions.
Another important light source consists of fluorescent lamps. A fluorescent lamp consists of a phosphor-coated glass envelope containing low pressure argon and mercury gas. Electrode's at each end of the envelope transport a net charge through the gas. This gaseous c
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