phototherapy
n. exposure to ultraviolet or infrared light used for treating certain medical conditions (e.g., jaundice, psoriasis), depression, and other disorders. For example, in phototherapy for seasonal affective disorder, a specially designed lamp that delivers 5,000 to 10,000 lx of light is shone on the retina, and a signal is transmitted via the optic nerve to the pineal gland, which secretes melatonin in response to darkness. Inhibition of melatonin release by bright light relieves the symptoms of SAD. Also called bright light therapy.