Of or pertaining to chemical action of light, or produced by it; as, the photochemical changes of the visual purple of the retina.

smog A colourless air pollution that occurs mostly in summer. It is produced when pollutants such as nitrogen oxides and organic compounds (produced by burning fossil fuels) react with sunlight in the atmosphere to form a gas called ozone.

of or relating to or produced by the effects of light on chemical systems

A term referring to the group of processes that allow a photographic image to be transferred to a printing element. This is frequently done by means of a dot screen through which the continuous gradations of photography are translated into spots of black and white.