Photoluminescent phosphors glow in dark after being stimulated with light. The period of time the phosphor continues to glow is called the Afterglow. The lower level of light emission that can be perceived by the human eye when adjusted for darkness is about 0.3mcd/m2. These phosphors are daylight stable, heat and temperature stable, non-toxic and free from any radio-active elements. These phosphors are made from types of rare earth and are completely different from the much lower performance Zinc Sulfide type pigments.