AFTER A bright October the grey dirge of the autumn is finally upon us. Before us lies the virtual daylessness of winter. A mind-crushing gloom grips the country like a suffocating blanket. God, it's depressing.

Winter gets me down. I don't know if I'm a full-blown Seasonal Affective Disorder (SAD) sufferer but I certainly had a propensity to write poems with titles like "November Hell" in younger years. I sink as the days get shorter.

You will have heard of light therapy. Eyebrows were raised when the idea of sitting next to a bright lamp was first mooted to beat the winter blues. Not any more. From this week Boots is selling its first portable light box. The Bright Spark retails at pounds 129 and is VAT-free - even the government believes in SAD. The latest research shows that prophylactic or preventative light treatment can stop SAD before it starts. If you know or suspect you are vulnerable, get your light in now to avoid trouble later.

"Get as much natural light as you can," advises Stephen Hayes, founder of Outside In, the Cambridge-based light therapy company. "Bright light increases serotonin in our brains, our natural feel-good chemical. Some people's level of serotonin production falls more steeply with light deprivation. There is a genetic vulnerability and it can be worse with bad weather and stressful life events."

A threshold of 2,500 lux is enough to help SAD people. On a bright day this means that just half an hour outside will keep you going. But on a dark day, no amount of hanging around in the open air will do. SAD-vulnerable people can start to sink after about three days of gloom. A brightly lit office or house can rarely provide even 1,000 lux. Which is why, when the clocks go back and office workers don't see daylight from one weekend to the next, they can run into problems.

Symptoms of SAD are similar to clinical depression. They include oversleeping and waking after a long sleep feeling unrefreshed, plus feelings of despair. Sufferers often show signs of a hibernatory animal (craving carbohydrates, not gathering nuts) and find normal tasks frustratingly difficult. Sufferers are likely to be renowned for leaving lights on round the house.

Seek enlightenment

1. Try to take a winter break in the sun - skiing can be good.

2. Don't make major decisions.

3. Sit near sunny windows and paint rooms in light colours (St Petersburgers paint their buildings in pastels). Go outside in the middle of the day.

4. Get a light box

5. Aerobic exercise raises serotonin levels. Vitamin B12 also seems to be helpful.