A dental plaque disclosing light for use in conjunction with a fluorescent dye plaque disclosing solution contained in a periodontal area of an individual's mouth is disclosed. A parabolic reflector supports a light source providing only light which causes the fluorescent dye to fluoresce. The light source is located in conjunction with the parabolic reflector to cause the parabolic reflector to project a solid, converging cone of light. Preferably, the light source is located forward of the focus of the parabolic reflector. A power supply is selectively connected to the light source for illuminating the light source. The power supply may be one or more batteries, and if the batteries are of the rechargeable type, a means for selectively recharging the batteries is connected to the batteries. A lens is supported adjacent the light source for projecting a solid, diverging cone of light having an axis concentric with the axis of the converging cone of light. A casing which supports the parabolic reflector also supports a reflecting surface adjacent the parabolic reflector such that, when the converging cone of light and diverging cone of light are directed toward the individual's mouth, the light reflected by the fluorescent dye is reflected by the reflecting surface and directed toward the individual's eyes. The light source may be a lamp and a filter means covering the lamp for filtering and passing therethrough only light which cuases the fluorescent dye to fluoresce.