Light and the circadian rhythm: The key to a good night’s sleep?

The cycle of sleep and wakefulness is one of the key human behaviours. We spend about a third of our lives asleep and cannot survive without it. When asleep, our brain memorises and processes information. Our body clears toxins and repairs itself, allowing us to function properly when awake. Even short-term sleep deprivation significantly affects our wellbeing. Most of us begin to fall apart after just one night without sleep and after three nights of missed sleep, we are functioning way below par. One study suggested that after 17-19 hours of staying awake , performance on cognitive tasks may be similar to having had too much to drink. These effects worsen over time. The longest documented period without sleep of just more than 11 days prompted serious cognitive and behavioural changes, problems with concentration and short term memory, paranoia and hallucinations. But while scientists have long understood the importance of getting enough sleep, the key part played by light exposure can sometimes be overlooked. Setting the body clock The reason light is so important is that it sets our circadian rhythm, or body clock, via specialised light sensors within the eye. Our eye detects the light and dark cycle within our environment and adjusts the body’s circadian rhythm so that the internal and external day coincide. This is so powerful that that people who have very severe eye damage can find their body clock is thrown off , leading to sleep problems. Without any access to light, the human body clock appears to drift, adding about half an hour on to its 24 hour cycle for each day of darkness. Jetlag is the most obvious example of the effect light can have. Exposure to light in the new time zone helps reset our body clock to local time, telling […]

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