Chasing the Sun: How the Science of Sunlight Shapes Our Bodies and Minds

by Linda Geddes

adults aged eighteen to sixty-four need to get seven to nine hours of sleep per night

(seven to eight hours for those over sixty-five),

2016 study found that people living in areas with elevated levels of light pollution tend to go to bed and wake up later than those living in darker areas.

One function of REM sleep appears to be fine-tuning our emotions. If we don’t get enough of it, we become less adept at reading other people’s facial expressions and body language, so our ability to empathise and communicate suffers.

Between 10 and 30 per cent of people in Western countries experience chronic insomnia, whereas just 1.5 per cent of Hadza and 2.5 per cent of San participants interviewed said that they regularly had problems falling or staying asleep.

During the summer, Amish people are exposed to an average daytime illuminance of 4,000 lux, whereas the average Brit is exposed to 587 lux. During winter, the Amish experience lower levels of daytime light – around 1,500 lux but for us indoor-dwelling Brits, the average daytime illuminance is just 210 lux:

One recent study found that exposure to an hour of low intensity blue light boosted people’s reaction times (a measure of alertness) by more than if they had consumed the equivalent of two cups of coffee. When caffeine and light were given together, people’s reactions were even faster.