In psoriasis, UVB phototherapy has been shown to be effective. A feature of psoriasis is localized inflammation mediated by the immune system. Ultraviolet radiation is known to suppress the immune system and reduce inflammatory responses. Light therapy for skin conditions like psoriasis usually use NB-UVB (311 nm wavelength) light waves. In UVB phototherapy the exposure time is very short (seconds to minutes depending on intensity of lamps and the person’s skin sensitivity). The time is controlled with a timer that turns off the lamps after the treatment time ends.