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Light therapy or phototherapy consists of exposure to specific wavelengths of light using lasers, light-emitting diodess, fluorescent lamps, dichroic lamps or very bright, full-spectrum light, for a prescribed amount of time. It has proven effective in treating seasonal affective disorder (SAD), and for some people it has ameliorated delayed sleep phase syndrome. It has recently been shown effective in non-seasonal depression.

Seasonal affective disorder

Full sunlight is preferred for seasonal affective disorder. Other treatments are based upon infrared light exposure. There are a number of products (such as light boxes) using very intense artificial illumination that are effective for Seasonal Affective Disorder. These products must provide 10,000 lux or more directed angularly at the user's eyes, while filtering out any harmful ultraviolet radiation. Modern light boxes do not emit ultraviolet radiation. New research indicates that using only certain wavelengths of light (i.e., the "blue" wavelengths) is at least as efficacious as using 10,000 lux bulbs[How to reference and link to summary or text].

Non-Seasonal depression

Only recently have clinical studies been conducted which specifically excluded all patients with any degree of seasonality.[1] Before these studies, there was suspicion that any depressed patients who benefitted from light treatment were really only having the SAD component of their depression treated. However, light therapy is now an established treatment for depression, regardless of seasonality[2][3] , and has certain advantages over drugs, in that it might take less time to see a benefit (typically antidepressant drugs take several weeks to reach full effectiveness).

Delayed sleep phase syndrome

When treating delayed sleep phase, the timing of the exposure is critical. The light must be provided as soon after arising as possible to achieve any effect. Some users have reported success with lights that turn on shortly before waking (dawn simulation).

Proposed mechanisms

Safety of phototherapy

Ultraviolet light causes progressive damage to human skin. This is mediated by genetic damage, collagen damage, as well as destruction of vitamin A and Vitamin C in the skin and free radical generation.

Visible blue light has been suggested to cause DNA breaks, but carcinogenesis has not been demonstrated, and enzymes within the cells are believed to repair the breaks reasonably well. However cancer has been induced in cells with deliberately damaged repair mechanisms.

Modern phototherapy lamps used in the treatment of Seasonal Affective Disorder do not emit ultraviolet light and are considered safe and effective for the intended purpose, as long as photosensitizing drugs are not being taken at the same time and in the absence of any existing eye conditions. Light therapy is a mood altering treatment, as just as with drug treatments, there is a possibility of triggering a manic state from a depressive state, causing anxiety, and other side effects. While these side-effects are usually controllable, it is recommended that patients undertake light-therapy under the supervision of an experienced clinician, rather than attempting to self-medicate.[4]

Other studies have shown that blue light may play a role in developing age-related macular degeneration (ARMD)[1][2][3].


  1. Goel N, Terman M, Terman JS, Macchi MM, Stewart JW. Controlled trial of bright light and negative air ions for chronic depression. Psychological Medicine 2005;35
  2. Wirz-Justice A, Benedetti F, Berger M, Lam RW, Martiny K, Terman M, Wu J. Chronotherapeutics (light and wake therapy) in affective disorders. Psychological Medicine 2005;35
  3. Science News, April 23, 2005 - Mood Brighteners: Light Therapy Gets Nod as Depression Buster" by Bruce Bower
  4. Terman M, Terman JS - Light therapy for seasonal and nonseasonal depression: efficacy, protocol, safety, and side effects. CNS Spectr. 2005;10:647-63

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