Light therapy is the treatment of choice in the UK for NHS specialist Seasonal Affective Disorder clinics. Seasonal Affective Disorder (SAD) affects many people to a degree; they sleep and eat slightly more in winter and dislike the dark mornings. For some however the symptoms are enough to disrupt their lives and cause considerable stress. These people have SAD. Research conducted in 1998 indicated that in Britain about 0.5 million people suffer from clinical SAD, with around 5 million having milder symptoms in varying degrees (the Winter Blues).

SAD stems from the lack of bright light in winter. It is not a psychosomatic or imaginary illness and it is recognised by the World Health Organisation and in the Psychiatrists "bible" DSM-IV. Researchers have proved that bright light entering the eyes makes a difference to brain chemistry by stimulating the nerve centres that control our daily rhythms and moods. For example, at daybreak, bright light suppresses the production of Melatonin - a substance that makes us drowsy. But the lack of bright light on dull days can hinder this natural waking up process. Exposure to bright light also increases the production of Serotonin, a neurotransmitter that carries signals between the nerves in the brain. Low levels of Serotonin are known to be a cause of depression and indeed this maps well onto what people say: tasks which are easy when you are well become frustratingly difficult when you are depressed.

Some of the symptoms that can be associated with Seasonal Affective Disorder are:

Logically enough light therapy is successful as a treatment because it boosts the supply of bright light. While going to a brightly lit climate whether up the mountains or somewhere hot is indeed a cure, it is not practical for most people. Light Therapy boosts the supply of bright light by using a lightbox or similar device. For most people using a therapy light for between 15 and 45 minutes daily will be sufficient to alleviate the symptoms of SAD. Users do not have to stare at the light, but can watch TV, read or similar, so long as they are allowing the light to reach the eyes at the right levels.

The brighter the light, the less time it takes to use. The effectiveness of a therapy light depends on the lux level. Lux is a measurement of how much light is falling on the eyes. If you sit close to a therapy light, more light will fall on your eyes, the lux will be greater and the time required for use will be shorter. It often isn't practical to sit too close to a therapy light, so it is important to know how close you need to be to a particular light for the amount of light falling on the eyes to reach an effective level. The maximum recommended level is 10,000 lux, that is about the same as a spring morning on a clear day and about 20 times brighter than a normal well lit office. Contrary to the old belief, therapy lights need not be a special daylight matching or 'full spectrum' type, simply changing the lamps in a room to these special types will not produce light to the required lux.

There is an international SAD light manufacturer's association, which has a code of practice, this code includes a trial system so a sufferer can discover whether or not lights help without undue financial risk, and which ensures lights are made to their published specification. The UK charity SADA also has a list of recommended suppliers. Bright lights can be obtained VAT free in the UK. SAD lights are officially medical devices in the EC so the manufacturer should be able to show you the official certificates to prove they conform.