This in vitro study was designed to evaluate the ability of fluorescent tubes and dental lights to help operators distinguish tissues (fissures), differentiate between tissues (at site dentinoenamel junction or between carious and sound dentin), and distinguish form of a tooth preparation (Class II and Class V cavities). Operators with normal color vision ranked the lights in order of preference for each type of specimen. In general, for the fluorescent illuminants, operators preferred lights with high color temperature values and high color rendering index values. A small group of color-blind observers indicated a preference for an illuminant of law color temperature and law color rendering index value. For dental lights, operators preferred a higher color temperature for examining fissures, the dentinoenamel junction, and the cavity preparation. No particular illuminant was preferred for distinguishing between carious and sound dentin. Many observers had dfficulty in choosing a preferred dental luminaire.