'A photo resistor - whose resistance decreases with increasing incident light intensity. It can also be referred to as a light-dependent resistor (LDR) - or photoconductor. Cells rely on the material''s ability to vary its resistance according to the amount of light striking the cell. The more light that strikes the cell - the lower the resistance. Wide range of resistance from about 600 ohms in bright light to one or two megaohms in darkness. The cells are also capable of reacting to a broad range of frequencies - including infrared (IR) - visible light - and ultraviolet (UV).'