Light therapy employs either natural or artificial light to treat various disorders, ranging from psoriasis and other skin diseases to soft bones and seasonal affective disorder (SAD), a type of depression that occurs during the winter.

Origins

Exposure to bright sunlight and to the ultraviolet rays of sun lamps has been used to treat skin diseases for many years. The application of light therapy for treating SAD dates from the late 1980s when doctors first recognized the link between depression and the long, dark days of mid winter. Practitioners

Light therapy may be administered by a physician, physical therapist, or psychologist. It is also carried out at home under instructions by a qualified health professional.

When It Is Used

Light therapy is now the treatment of choice for SAD, largely replacing the use of antidepressants and psychotherapy. Ultraviolet light has several uses. One is to treat psoriasis, often in conjunction with drugs, as well as other nonspecific skin conditions that cause itching. Another is to treat rickets (in children) or osteomalacia (in adults). These disorders, in which the bones become soft, are caused by a lack of vitamin D, which the body makes when the skin is exposed to sunlight. Elderly shut ins benefit from such treatment in two ways: The light therapy helps strengthen their bones, and at the same time helps them counter depression. Infants born with jaundice are also sometimes exposed to ultraviolet light. Other potential uses of light therapy include treatment for jet lag, sleep disorders, and the biorhythm problems that are often experienced by people who work at night.

How It Works

Exposure to varying levels of light affects the biological clock of all living creatures. In humans, lack of sunshine has a more profound psychological effect than was formerly recognized. (Some researchers estimate that 20 percent of people who live in the northern United States and Canada could benefit from light therapy, with women outnumbering men four to one.) Daylight stimulates the human brain to produce hormones and other brain chemicals that are essential for psychological and emotional well being. For most SAD sufferers, daily exposure to a few hours of very bright fluorescent lights relieves their symptoms as effectively as a winter vacation in the sunny tropics. Within four days of beginning treatment, most patients show a marked improvement-much more quickly than with anti depressant medication. Benefits seem to be the same whether therapy takes place during the day or night. Ultraviolet light also directly affects the skin in several ways: It promotes the manufacture of vitamin D and slows the growth of new skin cells in psoriasis. Its drying effect may help improve acne. In some people, however, sunlight triggers a flare up of acne; one should proceed with caution.

What to expect

The special fluorescent lights used for treating SAD are housed in boxes containing a reflector and a light diffusing cover. The treatments, which are simple, painless, inexpensive, and harmless when done properly, usually take two or three hours a day, although some people benefit from as little as half an hour of exposure. During a treatment, the patient can nap, read, or go about other quiet activities. New types of light therapy devices that would not interfere with a patient’s daily routine are being investigated. One of these is a computer controlled gadget that switches on a bright light early in the morning to simulate the arrival of dawn before the time of the usual winter sunrise. Studies at New York’s Columbia Presbyterian Medical Center, where the device was developed, found that test volunteers woke up feeling alert and vigorous.

Precautions

• Light therapy is effective only with lights for this purpose. Other types of bright lights, such as lamps and sunlamps, are not suitable.
• To avoid eye irritation and damage, do not look light source. Always cover the eyes of babies who are exposed to bright, direct light.
• Because ultraviolet light increases the risk of skin use should be carefully monitored by a doctor.