Light therapy'controlled exposure to bright light-continues to play a role in conventional medical practice as well as its alternative cousins. Its most typical applications operate by abortion through the skin: Doctors expose newborns to blue light to cure jaundice. And dermatologists frequently prescribe sunlight or ultraviolet light to heal psoriasis and certain kinds of dermatitis.

Lasers offer a form of light therapy on the cutting edge of medicine, so to speak. Their highly concentrated light beams are now used to perform surgical procedures and dentistry without damaging surrounding tissues and so are less invasive than the most finely honed scalpel.

But the core of phototherapy, as light therapy is also called, capitalizes on light's effects on the central nervous system, especially the body's clock. The form of light therapy, which focuses mainly on circadian (daily) and seasonal biorhythms, is under active investigation by researchers around the world. Mainly used to treat seasonal affective disorder (SAD), it may one day become part of standard treatment for nonseasonal depression, insomnia, jet lag, problems adjusting to working different shifts, premenstrual syndrome (PMS), menstrual irregularity, and other conditions.

Most of this newer form of light therapy involves short periods of exposure to an intense form of artificial light that simulates daylight. Its effectiveness results more from the light absorbed through the skin. The artificial lights used to regulate body rhythms need to be intense, because typical indoor lighting is far too weak to affect the hormones involved.