PHOTOCHROMIC 

Photochromics (PC’s) change from clear when indoors to colored when outdoors. Specifically, PC’s change color in response to ultraviolet (UV) light, usually from the sun or a blacklight. 

Photochromics behavior can be either Reversible or Irreversible. (Technically, all photochromism is defined as reversible but for simplicity we will use the term irreversible photochromic to describe irreversible photochemical reaction that yields a visible color change.)

Reversible PC's change color in the presence of UV light but return to their original state when the UV source is removed.  Some examples of reversible photochromic applications are Transitions^® lenses, screen printing inks, sunglasses, nail polish, and novelty items.

Irreversible PC's begin as one color and change to another color in response to UV exposure. These materials do not return to their original state when the UV source is removed. This makes them useful only for applications requiring a single use such as document security devices, UV curing measurement and sunburn prevention.