Light therapy or phototherapy consists of exposure to specific wavelengths of light usingvery bright, full-spectrum light for a prescribed amount of time. It has proven to be effective in treating seasonal affective disorder, chronic fatigue syndrome and delayed sleep phase syndrome. Phototherapy or bright light therapy has been shown to suppress the brain's secretion of melatonin.
Light therapy must provide 10,000 lux or more directed angularly at the user's eyes, while filtering out any harmful ultraviolet radiation. Devices used for this treatment are portable and capable of UV filtering. Modern phototherapy lamps used in psychiatry do not emit ultraviolet light and are considered to be safe and effective even in pregnancy.