Light therapy is used to treat Seasonal Affective Disorder (SAD). SAD occurs when the amount of light available is less, usually this happens in fall or winter. People who use light therapy also notice a difference, when there have been several days in a row when it has been excessively cloudy outside.

People who use light therapy have an artificial full-spectrum light or light box that they sit by. This light is used for a set or prescribed amount of time each day. It is a safe and effective treatment when used correctly, and there are few side effects. It is safe during pregnancy. It is also safe to do while a person is breast-feeding, and requires only 15 to 30 minutes a day. Results are often seen within a week of starting light therapy.

Light therapy is a proven treatment for Seasonal Affective Disorder (SAD). It is also recommended for conditions such as non-seasonal depression or insomnia. Some people also use it as a way to increase the effectiveness of anti-depressant medications. and it may make it possible to lower the amount of medication needed.

Just how effective was established in a Canadian Study in which 100 patients were randomly assigned to Prozac or a light box. The results were pretty equal with the light box reducing depression slightly more quickly.

Light therapy is being studied to find out whether it may help other conditions such as non-seasonal depression, Obsessive Compulsive Disorder, sleep disorders, Dementia and Attention-Deficit/Hyperactivity Disorder. It is hoped that light therapy will help people who struggle to keep their circadian rhythms in sync will be helped through light therapy.

If using light is that good, why isn't it known? Light box studies are often poorly funded, and due to problems of related to the control of light intake, are often poorly designed. The control group is hard to “control.” How do you put someone on a sham treatment for a control group? What happens when they want to go to the beach or go outside for a walk. That control has then been compromised, and the study would then be invalid.

In some people with Bipolar Disorder, light therapy has been shown to destabilize mood. There is one very small study that found morning light may be more likely to trigger manic symptoms than midday light. On the other hand, there is one study by Bendi that found that hospital stays were shorter for those who had rooms on the east side of the hospital. This stettudy was done on people who had Bipolar Depression.

Also there is a study on the effect of Vitamin D on many illnesses. They are about half way through the five year study.

Light therapy is not the same as light and dark therapy.