Researchers have developed a material that almost instantaneously changes from clear to dark blue when exposed to ultraviolet (UV) light, and it just as quickly reverts to clear when the light is turned off. The new material, one of a class called photochromics, could be useful in optical data storage as well as in super-fancy sunglasses. For more than a decade, researchers at Aoyama Gakuin University in Japan have been studying the light-sensitive properties of photochromic materials.