Scientifically, light is described as visible electromagnetic energy whose wavelength is measured in nanometers (nm) or billionths of a meter. The eye is sensitive only to the visible part of the electromagnetic spectrum, a narrow band with wavelengths of 380 to 750 nm. At the shorter wavelengths lie ultraviolet; x, and gamma rays; at the longer wavelengths are infrared radiation, microwaves, and television and radio transmissions (Fig. 23-1).
Pure white light consists of relatively equal quantities of electromagnetic energy over the visible range. When it is passed through a prism (Fig. 23-2), it is split into its component colors because the longer wavelengths are bent (refracted) less than the shorter ones.
Quality of Light. The most common light sources in dental offices are incandescent and fluorescent, neither of which are pure white light. An ordinary incandescent light bulb emits relatively higher concentrations of yellow light waves than of blue and blue-green, whereas fluorescent ceiling fix-
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