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Light therapy is very effective in treating depression if the depression is related to seasonal affective disorder (SAD). Most people experiencing this type of depression will find relief with light therapy. It is the preferred treatment for SAD, because it is well tolerated, does not require a prescription and is easily accessible. Although light therapy for depression is as effective as medication in the treatment of SAD, there are no conclusive studies showing that light therapy works with other forms of depression.
For some people, lower seasonal light levels can result in SAD. The shorter days of fall and winter can disrupt the body’s natural circadian rhythm, the body’s 24-hour clock that regulates sleeping and waking. The disruption of the circadian rhythm can cause sleep disturbances and depression. Light therapy for depression helps the body regain its natural circadian rhythm, allowing for normal sleep patterns and eliminating depression. Other forms of depression, such as clinical depression, pre-menstrual syndrome and bipolar disorder are not caused by disruptions in the circadian rhythm and seem to be unaffected by light therapy.
Light therapy for depression involves the use of specific forms of bright light. Light intensity is measured by lux, with bright sunlight measuring 10,000 lux. Tanning beds and household lights do not emit high enough lux or the correct type of light and are not effective.
Portable light boxes, made for light therapy, can reach 5,000 lux and provide the best intensity of light for therapeutic purposes. “Cool white” fluorescent lights produce less ultraviolet radiation than full-spectrum lights and, although they produce less lux, can be useful in light therapy. Exposure to 30 minutes of 10,000 lux is equal to an hour exposure of 5,000 lux.
A majority of people with SAD find that light therapy for depression is most effective when used during morning hours, though it sometimes works better during the afternoon or early evening. Each person’s natural circadian rhythm is different, so the amount of lux needed and the time exposed needs to be tailored to the specific person to achieve results. In most people, elimination of SAD-related depression can occur within a few days of beginning to use light therapy, although some people may not see relief for three weeks or more. In all SAD sufferers, the depression returns when light therapy is discontinued. Everyone responds differently to the amount of lux and to the time exposed to light, so the use of light therapy for depression should be monitored by a physician.