Against Complete Blackout Curtains For Sleep

Epistemic status: moderately confident that something like this is directionally true, but good data or arguments could change my mind. Note the lack of citations — this is based on memory.

Most rationalists I meet believe the following:

  1. Sleep is very important

  2. To get the best sleep, install blackout curtains strong enough to prevent any sunlight from coming in in the morning

I disagree with them. I believe point 2 is false for most people, and that natural light in the morning is helpful.

In my model of the world:

  • Your circadian rhythm figures out what time of day it is based on the amount of blue light hitting your pupils, and picks a time it thinks you should wake up

  • It’s important to wake up at a consistent time each day, so your circadian rhythm is your friend

By blocking out all light in the morning, you might get a short term increase in the number of hours you sleep, but I predict you will hurt your sleeping consistency (and potentially soon you will start staying up later, negating your benefits entirely).

If you are the sort of person whose body wants to wake up 3 hours after sunrise, let your body have a little bit of natural light to let it know that sunrise is coming. If you’re the sort of person who’s body wants to wake up with sunrise, I predict you’ll do best by waking up with sunrise.

My advice is to take the energy you were going to spend on blackout curtains, and instead spend it on smart lighting that automatically gets redder in the evening.

Exception: if your circadian rhythm is incompatible with the schedules of other people, you may want to black out your windows and use artificial lighting to simulate a later sunrise. For example, you may work in the UK, have coworkers in California, but be a morning lark.