Light plays a crucial role in regulating our body clock. That is why it is important to get at least half an hour of natural light a day, in every season. In winter, light therapy can lend a helping hand. Here is how.
How light shapes our circadian rhythm
Deep in the brain, our body clock runs on a cycle of roughly 24 hours, setting the pattern of sleeping and waking. When the sun rises, the photoreceptors in our retina tell the brain that it is time to get going, and at the same time halt the production of melatonin, the hormone that eases us towards sleep. On waking, a second process also begins: around sixteen hours later, it allows the brain to switch to rest mode and, helped by the onset of darkness, to restart melatonin production. ‘Light allows our circadian clock to synchronise with two key moments of the day, morning and evening. Both are equally important,’ stresses Bénédicte Wildhaber, occupational psychologist (FSP).
She continues: ‘Exposure to natural light is an excellent way to support your sleep. A great deal of research confirms that people who spend more time outdoors sleep better at night.’ Yet in winter it is not easy to get that exposure, especially in the morning. It does not take much for our internal clock to go awry when it is deprived of its daily ration of lux, the unit of illuminance, i.e. the amount of light falling on a given surface area. As the days shorten, the body struggles to synchronise its waking and resting phases, which can lead to chronic fatigue, mood swings and less restorative sleep. In medical terms, this is known as seasonal affective disorder (SAD), commonly called seasonal depression or the winter blues. It was first described in 1984 by the American researcher Norman Rosenthal and his team at the National Institute of Mental Health.
Light therapy: restoring your energy
Sunlight delivers between 3,000 and 50,000 lux, so, as you might imagine, an ordinary bulb will not do. Our specialist confirms: ‘At home, we are rarely exposed to more than 500 lux.’ That is why it is worth getting specialist equipment and taking professional advice. Several factors come into play when setting your body clock, and one of them is timing: choose carefully when you use the light source. Someone who struggles to fall asleep and gets out of bed on the wrong side can get their sleep and their smile back within a fortnight, with around twenty minutes a day in front of a lamp delivering 2,500 to 10,000 lux, positioned 30 cm from the face. Effects on energy levels can be felt after just four or five days of treatment. Conversely, people who tend to wake too early will benefit from the same duration of exposure, but towards the end of the day. In winter, or after a course of treatment, light therapy can also be used preventively. Start in September to avoid ending the year exhausted.
Blue light and sleep
Intensity is only part of the story: the quality of light matters too. Evening light tends towards yellow; morning light contains more blue. Worth knowing: some bulbs let you choose the colour tone and adjust the brightness to create a softly lit atmosphere that helps you drift off.
3 ways to keep your vitality up in winter
Small, practical habits can help your body through the cold season:
- Step into natural light as soon as you wake
Morning light is the main signal telling your brain to stop producing melatonin. Take a 15- to 20-minute walk outdoors each morning or consider using a light therapy lamp over breakfast.
Dawn simulators (sunrise alarm clocks) are also a gentle way to wake up. The light builds gradually and, at the end of the cycle, a sound invites you to open your eyes. When choosing a device, ask yourself: can you adjust how long the light takes to build? Does it start from complete darkness? And what sounds are available?
- Keep to a regular sleep schedule
When light levels are low, fixed bedtimes and waking times help keep your internal clock stable. Avoid long weekend lie-ins, which throw your body clock out of step with your weekday routine, an effect known as ‘social jet lag’.
- Optimise your sleep environment
The quality of your bedroom environment and of your bed and mattress also plays a vital part. Dimmer lighting, less screen time before bed, a comfortable bedroom temperature and a bed suited to your build all prepare the body for rest and reduce brief awakenings in the night.
