Seasonal Affective Disorder (SAD) commonly known as the winter blues is a particular form of depression that affects most people to a certain extent on gloomy winter days and is a problem in approximately 10% of the population (USA and UK). It is recognized by the DSM-IV-Tr, a manual that assists with the diagnosis of illnesses like depression. Symptoms often begin in late autumn or early winter and cease in spring.

Typical symptoms are:

• Change in sleep patterns, particularly difficulty waking or reduced quality of sleep
• Changes in eating habits, particularly weight gain and craving sweet or starchy foods
• Depressed mood
• Irritability
• Decreased energy levels
• Decreased socializing
• Decreased sex drive
• Decreased concentration

Light treatment has been shown in many studies around the world to be effective in alleviating or completely curing the effects of SAD. Two excellent books summarising this research are "Winter Blues" by Norman Rosenthal, and "Seasonal Affective Disorder" by Angela Smyth. Light levels need to be between 2500 and 10000 lux (much higher than standard room lighting of 500 lux). It can be used instead of or in conjunction drug therapy and has many advantages over other treatments such as which include:

• It is non-invasive, benign, and cheaper
• It has only occasional mild and temporary side effects which might include a slight headache, nausea, sore eyes or feeling agitated
• It is fast acting - benefits are typically noticed within 4 days (although can be up to three weeks).
• It has a high success rate (typically 50-80% of SAD sufferers respond dramatically)