Light therapy—or phototherapy, classically referred to as heliotherapy—consists of exposure to daylight or to specific wavelengths of light using polychromatic polarised light, lasers, light-emitting diodes, fluorescent lamps, dichroic lamps or very bright, full-spectrum light. The light is administered for a prescribed amount of time and, in some cases, at a specific time of day.
One common use of the term is associated with the treatment of skin disorders, chiefly psoriasis, acne vulgaris, eczema and neonatal jaundice.Light therapy which strikes the retina of the eyes is used to treat diabetic retinopathy and also circadian rhythm disorders such as delayed sleep phase disorder and can also be used to treat seasonal affective disorder, with some support for its use also with non-seasonal psychiatric disorders.