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How Does Light Affect Sleep?

Updated: Mar 2, 2023

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A while back, I was talking briefly on social media about how light can affect sleep. You all showed a lot of interest in it and, when polled, said you definitely wanted to learn more about it.'s been a hot minute (hello #3under3), but I'm finally getting you more information about it!

The Brain and Light Sensitivity

The brain is a powerhouse. It keeps track of what's going on in our bodies and what's needed for our bodies. When something is needed, the body relays that to the brain and the brain responds by sending signals to wherever in the body needs to act. Did you know your brain is involved in you walking across the room, feeling hungry, and sleeping? Yes...your brain helps you sleep!

Your body gets onto a natural rhythm that is based on the flow of day and night where you are. Sunlight has a huge part to do with that. This is why people on the other side of the world can have daytime while you are sleeping, and vice versa. It's also why you feel jet lag if you cross multiple timezones. Even if your body isn't on a set schedule every day, it will feel the difference of a few hours or more. Your body clock is naturally based on the flow of day and night where you are.

So, the brain receives the signal that it's time to sleep from multiple factors. First, fatigue from being awake all day (or a certain wake window for babies and young children) will tell your body that you are tired. Second, the sun going down and the world around you getting dimmer will also tell your brain that it's time for sleep. However, in today's world, we have no shortage of light- even when the sun has gone to bed. This can be confusing to the brain. When your brain sees light, it thinks, "time to be awake!" When your brain sees darkness, it registers that it's time for sleep.

Melatonin is a natural hormone that our body produces to help us sleep. (Yes, there are supplements as well- read my thoughts on that here.) When the body is in darkness, it increases the production of melatonin. On the other hand, cortisol is a natural hormone that helps us wake up. When light is present, the body increases production of cortisol.

This is why light and darkness play such a huge role in our sleep. You want your sleep environment to be as dark as possible. Your body can then recognize that it's time for sleep and will produce natural melatonin to aid you in sleeping.

Light experiment: Close your eyes and leave the light on. Then turn the light off, keeping your eyes closed. Can you see the difference? I can tell when my husband is on his phone in our dark room, even when my eyes are closed. The brain can register light through the eyelid.

Best Color Light for Sleeping

You've probably heard the term "blue light," and you've likely heard me talk about red light as well. Even the color of light can affect how the body prepares for sleep. If you do need light in your sleep environment before bed, for whatever reason, red light is the least inhibiting of melatonin production. Blue light- the light emitted from televisions, tablets, computers, and cell phones, is the most inhibiting of melatonin prodution.

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Did you know that you also get blue light exposure from the sun? When you get this natural exposure during the day, it helps your production of cortisol and melatonin stay regular. However, when you get blue light exposure during the day and in the evening (from screens), the hormone production will be off. I have had clients tell me their child watches TV to wind down before bed, or uses a story app during their bedtime routine. These activities are counterproductive to settling the child down. Screens will encourage the body to stay awake.

Color Study

There was a study done that exposed a sample of men to four different light varieties: bright white light, dim light, red light, and blue light. They tested their cortisol levels after exposure. They were questioning: does blue light increase cortisol and does red light lower cortisol? What they found was increased levels of cortisol after exposure to the bright white light and the blue light. Decreased levels of cortisol were found in those only exposed to dim light and red light. You can read the National Library of Medicine study abstract here.

Another study was done on a Chinese women's basketball team. Half of the team was given red-light therapy for 14 days and the other half was given a placebo light therapy. After 14 days, they noted increased melatonin levels, improved sleep, and better endurance performance in the players who received the red-light therapy. You can ready that study abstract here.

We use a Hatch Rest light in Gideon and Phoebe's room. We have it set to turn red at bedtime and then green at 7:00am. So, Gideon knows that if he wakes up and the light is still red, he has to stay in his bed. Once it turns green, he's allowed to get up for the day. This is the only light in their room at night and I have it set very dim during the night (literally only 1%). Research like the ones done above show us that if you are going to have any light on in a bedroom at night, red light is the best option.

The Darker the Better

So, what does all of this mean? Well, if you want to be able to fall asleep quickly and sleep as deeply as possible, then the sleep environment needs to be as dark as possible. Also, blue light right before bedtime is telling your body to produce cortisol, which will keep you awake. If you are falling asleep in front of the TV or scrolling through your phone right before bed, this is not going to support good sleep for your body. This is true for anyone, babies on up through adulthood.

At times, I am guilty of the mindless bedtime phone scroll just as much as anyone else. However, when I am at my healthiest, my bedtime routine is to put my phone down and read in bed before I go to sleep. I read from a real book, not an electronic one, only using the light of the lamp on my nightstand. When I do this, I notice a HUGE difference in my ability to fall asleep quicker and sleep deeper through the night!


Is there anything about yours or your child's sleep environment or bedtime routine that you can change to encourage better sleep? I highly recommend trying it for a few days and see if you notice a difference!

I'd love to hear from you! What is something you found interesting about light and sleep? Comment to let me know.

~Ashley Bell, pediatric sleep consultant

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