Sleep is important for our health. It is important to sleep in the dark. Sleeping with the light on could be bad for us. Turning off the light helps to keep away diabetes and heart disease. Around 40 per cent of people sleep with some sort of artificial light, like a television or alarm clock. The worst thing is sleeping with a main light. Sleeping in the dark is more difficult for people in cities. This is because there is a lot of outdoor light at night.

Dr Phyllis Zee is an expert in sleep medicine. She said it is healthier to turn off lights when we sleep. She did a study on the blood sugar levels of 20 people. The people who slept with a light on had higher sugar levels than those who slept in the dark. Dr Zee said light makes the brain active, which raises blood sugar. There are three things we can do: turn off the lights, never sleep with white or blue light; and wear an eye mask.