Question: Is it better to sleep in complete darkness or with a bit of light?

Rachel Sharman answered on 5 Nov 2018:

Hi,

What a brilliant and tricky question! It depends on the time of year, your age/chronotype, and where you are in the world!!!

So we have this pathway of nerve cells that goes directly from the eye to the area of the brain where the body clock is located (suprachiasmatic nucleus). This pathway (the retinohypothalamic pathway) is absolutely nothing to do with sight but allows the body to recognise light and dark.
It tells our body clock to wake up if it is light out or enter rest when it is dark.

We used to say an absolutely dark bedroom is best for sleep, and it is for adults, as then the body clock knows it is time for sleep. However, more studies are now showing that we can receive light information through our eyelids when they are closed and this can tell the body clock what time it is, even if we arent awake!

One of the things you can do if you are sleepy in the morning is get light as soon as you wake up. Daylight is great! This can reset your clock. (Light in the evening, like from phones, is bad because it tells your clock to stay awake as its a similar wavelength to dawn light!).

When dawn isnt occurring too early (like in the summer) and its dark outside, as long as there are no streetlights outside, I always tell the teenagers on our study to sleep with their curtains open as the dawn light will help wake them up, even if they dont have their eyes open! In summer, dawn is really early, so unless you want to wake up at dawn, a dark bedroom with thick curtains is best and make sure to get light as soon as you wake up (I eat breakfast outside!).