Photochromism is the phenomenon in which reversible change of color takes place upon exposure to light. Photochromic pigments absorb energy and change color in the presence of ultraviolet light. Photochromic pigments are suitable to be printed on various kinds of materials. Photochromic pigments have various features such as color changing ability, easy solubility in water, excellent water compatibility, excellent abrasion or adhesion properties, high brilliance, gassing stability, and high hiding power and narrow particle size distribution, and long shelf-life. Photochromic pigments find applications in paints; suitable for usage in surface coating products such as PMMA paint, ABS spray paint, PVC paint, and water-based spray paint, inks; suitable to be printed on various kinds of materials, such as fabrics, paper, synthetic membrane, and glass, and plastic products; plastic injection and extrusion using high color density PE, and industrial applications such as textile and printing. They are specifically designed for usage in non-aqueous-based ink systems, and most importantly sunglasses and lenses.