Light may affect the growth of crystals if they are light sensitive. An example of this is the formation of ice crystals on silver iodide. Ice crystals form on the surface of silver iodide when illuminated with white, but not red light.
The polarization of light from an infrared laser may affect the structure of a crystal. Light can also speed up the nucleation rate, which describes the formation of the crystal component, but not the growth of the crystal structure that is visible. Crystals of silver bromide and silver iodide, two components of photographic film, decompose to silver metal when exposed to light.