Daylight has a powerful effect on our 24 hour body-clock, especially sunrise, our natural alarm clock. Enabling the early birds amongst us to ‘catch the worm’, sunrise also ensured that we were awake and not ‘the worm’ when predators were up and about. An extreme example of the effects of daylight on when and for how long we sleep, are the Inuit, in northern Canada who, until recently, only depended on oil-lamps at night. They would sleep and doze for around fourteen hours a day during the perpetual darkness of the winter, whereas under the continuous daylight of the summer this fell to about six hours daily. Despite having eight fewer hours sleep, there was no increase in daytime sleepiness - it seems that the extra sleep in the winter was superfluous. Our modern living routines together with the electric light, result in little by way of seasonal changes to our sleep, despite the roughly eight hour seasonal difference in daylight in the UK. Nevertheless, we still have the ability gradually to extend our night-time sleep, not as much as the Inuit, but by about one to two hours, or even slowly reduce it to about six hours, given the time and inclination to do so, and without noticeable changes to daytime alertness. On the other hand, a sudden loss of an hour’s sleep as when clocks go forward, for example, can lead to more sleepiness, for a day or two until sleep has re-adjusted. Much of the effect of daylight on sleep is via the brain’s pineal gland secreting melatonin, also known as the ‘hormone of the night’. It is not really a sleep-inducer as it is also found at night in nocturnal animals. Instead, it tells us when to sleep and when to wake up, rather than how to sleep. Melatonin is knocked out by daylight and indoor bright light, especially by light with a slightly blue tinge. Bright light at night is also useful as a ‘quick fix’ for sleepiness, especially for shiftworkers. However, this alerting effect is not only due to the suppression of melatonin, but to other, more rapid, temporary action on other brain mechanisms. For dealing with ‘jet lag’ the judicious use of light is just as effective as melatonin tablets, especially as the tablets are useless in daylight. Another useful trick with light, but for babies, is for their daytime naps to be in the light, not in a darkened room. This naturally shortens their daytime sleep, leading to longer and better sleep at night.