Light therapy or phototherapy consists of exposure to daylight or to specific wavelengths of light using lasers, LEDs, fluorescent lamps, dichroic lamps or very bright, full-spectrum light, for a prescribed amount of time and, in some cases, at a specific time of day. It has proven effective in treating Acne vulgaris, seasonal affective disorder, and is part of the standard treatment regimen for delayed sleep phase syndrome. It has recently been shown effective in non-seasonal depression. Proponents claim demonstrable benefits for skin conditions such as psoriasis.