The effect of temperature on the luminance of various types of aids to military activity under cover of darkness has been measured at temperatures ranging between -60°and 200°F. The luminance of fluorescent materials appears to have a maximum value near 75°F with very little change between 60° and 80°F and dropping no more than 20 percent at the extreme tempera¬tures. The luminance characteristics of phosphorescent materials were affected markedly by the temperature. For a constant intensity of excitation, phosphorescent materials appear to have a maximum intensity at about 75°F. The luminance-decay rate of both a high initial brightness (HIB) and low initial brightness (LIB) material was increased with increasing temperatures. At higher temperatures, above 75°F, the rate of luminance decay of the HIB material was so rapid that its usefulness was destroyed. Below 75°F the rate of luminance decay was greatly retarded until at -60°F the luminous life for both the HIB and LIB specimens is about equal. Temperature has essen¬tially no effect on the luminance of the radioactive self-luminous materials throughout the range used in this series of measurements (-60°to 150°F). However, at about -60°F the luminance begins to drop appreciably. One fea¬ture noted in raising or lowering the temperature of a glowing phosphorescent specimen after irradiating at a selected temperature is that the glow can be stopped by cooling and restored again when the temperature is raised (heat¬ing enhances the glow). A comparative measure of the absorbed phosphores¬cent energy at various temperatures of a constant irradiation was made. More energy is absorbed at -60°F than at higher temperatures.
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