Light and sleep

More light during the day - better sleep at night

Introduction
Light is a very important factor in regulating our sleep-wake cycles. In nature, light is gradually replacing darkness in the morning, getting brightest around midday and decreasing in intensity towards the dusk. Regular exposure to light overday and darkness overnight keeps our biological clock in sync with the 24 hours of the rotation of the Earth.
Light can actively shift our internal clock: bright light in the morning can advance the biological clock, and bright light in the evening can delay it.
Besides shifting our clock, bright light makes us more alert and less tired at any time of day.

Falling asleep
The ability to fall asleep is determined by the time since we’ve woken up (actually by the so called sleep pressure) and by the phase of our biological clock. Normally we sleep during the night, but many people also feel sleepy in the early afternoon and some even take a short nap.

Melatonin
In the evening of our biological clock, our body starts producing melatonin, the hormone of darkness, and we start feeling sleepy. Bright light increases alertness and in the evening and during the night bright light suppresses the production of melatonin. Therefore, prolonged exposure to strong light in the evening can delay the moment of falling asleep.

More light during the day - better sleep at night
Scientific studies show positive effects of overday bright light exposure on the quality of night sleep, both subjectively and objectively. Bright light during the day can lead to stronger production of melatonin during the night, which can influence sleep quality.
Especially in times when one does not receive natural light (winter season), people can benefit from additional exposure to bright light during the day. A specific group in need of bright light are the elderly. Due to reduced mobility many of them are less exposed to outdoor light. In addition reduced amounts of light reach their retinas due to reduction of pupil size and reduced transparency of the eye lenses with age. Application of extra light is supporting their vision, as well as improving regulation of their sleep wake rhythm.

Sleep problems
Some of the sleep problems may be caused by desynchronisation of the biological clock.
For example, if the internal clock is extremely late (as in delayed sleep phase syndrome), the person will have difficulties falling asleep at any acceptable time in the evening, laying awake till shortly before the time when the alarm goes off. Unrested, this person starts the working day. As the condition persists, one faces chronic tiredness, seaks help in sleeping pills and enters the vicious circle. Once diagnosed properly, this condition can be successfully treated by morning bright light therapy.
The opposite situation is advanced sleep phase syndrome, caused by a very fast biological clock. A person suffering from advanced sleep phase syndrome gets very sleepy early in the evening, and wakes up in the middle of the night. This is impairing participation in social activities. Bright light therapy in the evening can help tuning the biological clock to the external time, and resolving the sleep problem.

Look for help
Sleep problems may be caused by many other factors, and it is advisable to search professional help before starting self treatment. Although light treatment brings limited side effects, light therapy of serious problems should only be done under supervision of a professional therapist, and after correct diagnosis.