Phosphorescent and Fluorescent Pigments
Outstanding examples of new developments in colorants are the phosphorescent and the fluorescent pigments. In many fields their possible uses are only now being explored. These pigments have several unusual characteristics. A phosphorescent pigment, or color, will glow when exposed to invisible ultraviolet light rays, and it will continue to glow some time after the ultraviolet rays are cut off. Such colors contain phosphor compounds which have the property of being able to trap light energy and emit it later, after the source of activation has been discontinued. How much later this can be done varies from millionths of a second to days depending on the compound. What we see as “color that glows in the dark” is actually stored-up light energy being emitted by the phosphor compounds which at some previous time have been exposed to light.
After thorough exposure to ultraviolet light, r black light, most phosphorescent pigments have a sufficiently high initial brightness in the dark to be viewed by the eye as distinctive colors. The range of colors available, however, is limited to blue, blue-green, green, yellow, yellow-orange, and variations of these colors.
Fluorescent pigments, on the other hand, actually capture and transmute absorbed visible and invisible rays into the dominant color visible to the eye. This makes the pigments appear to glow, or emit light themselves, when seen under normal light conditions.
Fluorescent pigments, available in a full range of very intense fluorescent colors from red to blue, make it possible to produce very brilliant color effects such as Day-Glo. “Daylight “ fluorescent products retain their visibility and color effect at distances up to four times as great as the brightest of ordinary materials. However, fluorescent brightness is controlled by the intensity of the exciting light and by the nature and amount of fluorescent pigments used in the finished material. Glowing color at present has one shortcoming; it fades under strong sunlight and loses its fluorescent quality quite rapidly. Artificial light does not cause fading. The major differences between the fluorescent and the phosphorescent pigments is that the fluorescent pigments are not visible in the dark.