Light therapy, a method clinically backed by data investigated for over two decades, is used to treat a depression called seasonal affective disorder or SAD. For this, a device called a light therapy box is mainly used usually for approximately 30 minutes daily. The function of the light therapy is to cause a change in the brain by mimicking outdoor light that would liven up the mood of the person affected and reduce the symptoms of the depression. The light used is generally 25 times as bright as normal room light. A study published by Dr. Michael Terman uses an apparatus with fluorescent bulbs which disallow UV radiation through a filter, leaving out unpleasant glare. This when applied as treatment on SAD patients upon awakening found it better than those who used it in the evening. Another group of thirteen specialists from Canada issued guidelines for treating SAD. These professional guidelines include conclusions like 10,000 lux for 30 minutes per day using a light therapy box as a starting dose. If a light box emanates 2,500 lux, it would require two responses in a day. The therapy should start early morning where it would maximize response which would usually show within a week, but may be effective from week four in some cases. The side effects of such therapy could include headache, strain on the eyes, nausea and agitation. Generally mild in nature, these effects disappear with reducing the dose of light.

The therapy boxes are also called light boxes, bright light therapy boxes and phototherapy boxes. The Center for Environmental Therapeutics (CET) recommends requirements for effective therapy as many products in the market claiming to be proficient to help SAD may not be so. These include things like checking whether the product is tested through trials under peer-reviews. One should also verify specifications of the product like whether or not it has a sufficient output like an illumination of 10,000 lux at a comfortable sitting distance.

In a light therapy box, the UV filters if faulty could cause harm to the eyes and skin by allowing UV rays to pass through. The fluorescent lamps should therefore have a diffusing panel and should give off white light rather than a colored light. A compact light box is also not as efficient in therapy as the small head movements render the eyes out of the range of therapy. The angle at which the light reaches the eyes, if projected downward, minimizes glare leading to less eye strain.

Such things recommended by the CET should be kept in mind while buying light boxes for therapy. The quantity rather than the quality is effective in the therapy of seasonal affective disorder.