SAD and light therapy

How light affects you

Like any other animal, human beings are sensitive to seasonal changes in daylight. Many people find that they eat and sleep more during winter - they experience unexplained mood swings and have difficulty concentrating or getting out of bed. Some people also develop an excessive appetite for 'comfort foods' that are rich in sugar and carbohydrates, such as pasta and chocolate. As a result, they may experience a seasonal increase in weight.

The winter blues and SAD

When these symptoms occur during autumn and winter, they're called the 'winter blues'. The winter blues are also called subsyndromal SAD (or sub-SAD) and are a milder variant of Seasonal Affective Disorder (SAD), or winter depression.

In this section

They typically occur from September to March during the shorter days of the year. As many as 60% of people experience at least one of the symptoms of the winter blues, whereas only 2% suffer from true winter depression, showing similar symptoms in more severe form.

The winter blues are not specific to people of a certain race, skin colour or social status. There does seem to be a difference between men and women, however - as far as we know, about twice as many women as men have the winter blues.

Light - or the absence of it - causes biochemical changes in our body that affect our overall sense of wellbeing. Light is measured in lux, a unit that indicates the intensity of light. In winter, light intensity levels are generally much lower than in summer - on a dull winter's day, light levels vary between 2,000 and 10,000 lux, whereas in summer they may reach 100,000 lux. In winter, we also spend most of our time indoors at home or at the office, where artificial lighting yields even lower light levels of only 0-500 lux.

What the experts say

Many medical experts and scientists agree that a lack of bright light, that is to say light of a specific intensity, can cause us to feel less energetic. Although they are still researching the exact nature of this relation, there is extensive evidence that regular exposure to additional bright light makes us feel more positive and energetic.

There are a number of theories about how bright light causes biochemical changes in our body and how this affects our wellbeing:
Several studies relate the winter blues to an inability to adjust our biological clock in winter. Instinctively, we live our lives by our internal (circadian) clock, which has a rhythm of slightly less than 25 hours.

Everyday life, however, makes us follow a strict 24-hour routine. In winter, people who are sensitive to the decrease in light are unable to catch up on the missing hour.

It has also been argued that the patterns of light and dark affect serotonin, a neurotransmitter that regulates our mood, appetite and energy levels, and the production of the hormone melatonin. A lack of daylight results in excessive melatonin production, which makes us feel depressed.

How to put more light in your life

You can't change the seasons, but you can do something about your energy level - make sure you get a sufficient amount of bright light! Philips has developed a special light device, Bright Light Energy, which allows you to safely absorb the amount of light you need to restore your physical and mental wellbeing.

Clinical tests have shown that Bright Light Energy really works. Regular light sessions with Bright Light Energy proved to be effective in approximately 90% of cases. Light therapy is generally accepted as one of the most effective and safest ways of dispersing light-related symptoms, including the winter blues.