85% of diagnosed cases of SAD respond to light therapy. This means exposure to very bright light (at least 10 times brighter than ordinary domestic light) for up to 4 hours a day.

Average domestic or office lighting emits an intensity of 200-500 lux (the technical measurement for brightness). 

The minimum requirement to treat SAD is closer to 2500 lux.  Natural light on a bright summer's day can be measured at 100,000 lux.

Light therapy should be started in the autumn as the first symptoms appear, and continued daily until the spring.  It is usually effective within 3 or 4 days of commencement, and benefits continue as long as some time is spent using the light therapy device each day.

Whilst undertaking light therapy, the sufferer can continue to carry out normal tasks, such as working, reading, or eating a meal.  The proximity of the light source is also important.  The closer the sufferer is to it, the more effective it will be, as more light can enter the eyes. 

It is not necessary to stare directly at the light during treatment, although this has been proved safe.  Tinted glasses, or other items that stop light reaching the retina, should be removed.

There are a number of devices that can provide light therapy.  They range from light visors worn on the head, to alarm clocks and light boxes.  They vary in strength and effectiveness.

As SAD becomes more widely accepted as a medical condition, a small amount of specialist clinics are being set up within the NHS.  However, at the time of writing, light-therapy devices must be purchased by the individual, and are not available through your GP or hospital.

02/06/2009