High object visibility is a necessary characteristic of traffic control devices and a significant factor in highway safety. Fluorescent pigments, which possess unique physical properties that provide high visibility characteristics not provided by conventional pigments, are now used for safety markings and to a limited extent in the traffic field. Fluorescent and conventional pigments have substantially different spectral energy radiation patterns. Fluorescent pigments absorb energy from the near visible ultraviolet blue and green region of the electromagnetic spectrum and remit this energy in a very narrow band of the spectrum. Conventional pigments simply absorb and reflect incident light. Properties of a selected group of fluorescent and conventional pigments are shown as well as the spectral response of the human eye and various source illumination distributions. The field study considered variations of daylight energy distribution under clear and overcast sky conditions, representative solar altitudes, and the cardinal directions. Two fluorescent and four conventional high visibility pigments were viewed against representative backgrounds. Although, detection and identification of fluorescent pigments are comparable to conventional high visibility pigments under optimum viewing conditions, fluorescent pigments show substantial improvements as illumination levels decrease or when the target situation is least advantageous.
Abstract