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Bright light therapy for seasonal affective disorder

NOV 2008

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Bright white light therapy has been used to treat seasonal affective disorder for more than 20 years. In this video, Dr. Michael Miller, editor in chief of the Harvard Mental Health Letter, discusses how bright light therapy works.


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How to choose a light box; what precautions to take

The best advice is to work with your clinician to select the type of bright light therapy that suits your individual needs and minimizes any risks. A few pointers follow.

Bright light box basics

  • A bright light box is designed to mimic the type of intense light you get outdoors. Merely sitting in front of a lamp at home won’t alleviate symptoms.

  • Although various devices exist, a standard bright light box uses rows of fluorescent bulbs that are backed by a reflective surface, so that as much light as possible reaches the patient.

  • The standard dose of light is 10,000 lux for 30 minutes each day. Lux is a measure of illumination. If you walk outside on a bright, sunny day, you’re exposed to about 50,000 lux of sunlight.

  • To benefit from light therapy, you have to position yourself at the proper distance from the light box. That’s because lux is a measure of the light a patient receives — not what the device produces. (Check with your clinician to determine the proper seating.)

  • Light boxes are expensive — they can cost $200 or $300 — and health insurance doesn’t always cover the cost. Check your policy.


Although light box therapy is safe overall, a few precautions apply.

  • It’s important to protect your skin and your eyes, which can both be damaged by ultraviolet rays that are contained in light. A good light box includes a Plexiglas cover in front of the bulbs to screen out ultraviolet rays.

  • To get the best results, position the box at an angle, so that the light reaches your eyes indirectly. Don’t look directly at the light box, which will damage your eyes.

  • Although light therapy is generally safe, people with bipolar disorder may become manic after too much light exposure. And people with any kind of retina disease or diabetes are at greater risk for eye damage than others.

  • Certain supplements and medications can also increase the risk of eye damage, because they make the retinas more sensitive to light. These include melatonin, lithium, and St. John’s wort.

Emerging technology

  • Newer and smaller devices use light-emitting diodes. These devices are about the size of a paperback book, or a portable mirror.

  • LED technology has also enabled researchers to start experimenting with different colors of light, to see if any are more effective than the others. After studies in animals suggested that cells in the retina are most sensitive to the effects of blue light, researchers began testing blue-light devices in people. Although blue light devices are being sold commercially, the experts advise against using them — at least until more is known about how they work.

  • There is also no evidence that light visors and other headgear are effective.