Marks Daily Apple
Serving up health and fitness insights (daily, of course) with a side of irreverence.
4 Mar

How Light Affects Our Sleep

Blue Light ComputerMost people are at least cursorily familiar with the concept of the circadian rhythm. For those who aren’t, the circadian rhythm refers to our internal, approximately 24-hour cycle of biochemical, physiological, and behavioral processes. Every living thing, from fungus to bacteria to plant to animal, has a circadian rhythm. External cues called zeitgebers (what a great word, huh?) help synchronize or alter our rhythms; they include temperature, nutrition, meal timing, social interactions pharmacological interventions (medicines, drugs), and, most prominently, the light/dark cycle of the earth.

Yes, light, or the lack thereof, plays an enormous role in the regulation of our cycles, especially our sleep cycle. For millions of years, light was an objective, exogenous measure by which organisms established behavioral patterns, hormonal fluctuations, and sleep cycles. Depending on the seasons, the position of the global axes, and the weather, you could pretty much count on light, bright days and deep, dark nights. Nocturnal hunters and scavengers took the lack of light to mean “eatin’ time,” while other animals (including humans) sought shelter and slumber when night fell. Daylight meant activity and safety (since we could, you know, see everything). Fire, then, wasn’t just about cooking and providing warmth; it also allowed humans a small sliver of daylight’s safety and security at night.

Before I go on, I need to make something clear. My regular readers will have already grasped this concept, but I think it’s a good idea to reiterate it. Though it’s tempting to place us humans on another plane of existence, apart from the mindless flora and fauna that share this world, we are animals. Sure, we’re smarter and more complex than the others, but we’re still subject to these exogenous zeitgebers worming their influential fingers into our subconscious and fiddling with our circadian rhythms. Our tendency to get sleepy when night falls isn’t a cultural relic; we didn’t consciously decide to start sleeping at night because it was too dangerous to be out in the dark. The culture of standard bedtimes arose organically, if you can even call it culture. Does the chirping of birds in the morning reflect cultural tendencies? Is “the early bird gets the worm” a standard axiom in avian academia? No – the early bird’s evolutionary niche decrees that it wake up bright and early in order to get food. It’s basic natural selection, and humans are the same way. We don’t decide to get up early. We get up early because of a complex pattern of environmental cues telling us to get up. Throughout our evolutionary development, handling business during the daytime was simply how we survived. We can’t escape nature.

But boy do we try.

The zeitgeber (can’t get enough of that word) with the biggest impact on our sleep cycle is light. Period. And it’s not just natural light that affects our sleep cycle, but also unnatural, manmade lights. That’s kinda how we operate, actually, as instinctual beings who often misinterpret “unnatural” because, well, our physiology isn’t exactly intelligent. It’s not sentient. It’s purely reactive. Blue light from a 10:00 AM sky, blue light from your computer screen at midnight – it makes no difference to our circadian rhythms. It’s all the same to our bodies, because for millions of years blue light meant daylight, not a late night blog comment section or reruns of The Daily Show. And it’s the blue light specifically that appears to monitor our sleep patterns the most.

Like insulin and inflammation, blue light is integral to our health – in the correct amounts. When we’re exposed to levels of anything in excess (or too little) of what we would have experienced for the bulk of our evolutionary history, problems arise. Blue light regulates our secretion of melatonin, the sleep hormone. Exposed to blue light, we limit the production of melatonin, and we stay alert and awake; in the absence of blue light, melatonin production ramps up, and we get sleepy. This system worked quite well for a long time. Reddish light from fire (our formerly primary source of nighttime illumination) has little to no effect on melatonin production, so sleep wasn’t disrupted when we relied on fire. These days, though, we’re subject to a steady barrage of blue light. During the day, blue light (natural or unnatural) isn’t much of a problem because we’re supposed to be awake, but at night, when we’re “supposed” to be getting ready to sleep, we tend to sit in front of blue light-emanating appliances, and our sleep suffers for it.

(An interesting note on how we respond to blue light. For years, scientists assumed circadian rhythm was set by sight (of light) alone. Person sees sky/LCD screen and the same visual system that allows colored vision determines the hormonal, behavioral, or other physical reactions to the light. It makes sense, but that’s not how it works. It turns out that there exists a second, more dominant system responsible for setting circadian rhythm based on light input. If a person’s sleep cycle depended purely on traditional color vision, we’d expect the blind to universally suffer from disrupted sleep. They do not, however, and this is explained by optical cells that express a photopigment called melanopsin. Unlike the standard rod and cone opsins, melanopsin doesn’t help us see. Instead, it reacts most strongly to blue light, and scientists think it’s the primary regulator of the biological clock and production of melatonin. In otherwise blind patients with intact melanopsin systems, blue light has a strong effect on their sleep cycles.)

Blue light has its place, of course. A British study found that blue light-enhanced white lights in the workplace improved alertness, performance, and even nighttime sleep quality in employees. That’s during the day, though, when blue light exposure is normal and expected. Nighttime exposure to blue light disrupts our sleep hormones. Television, computer screens, even digital clocks with blue numbers – they’re all common sources of late night blue light that can affect our production of melatonin.

Is blue light the only issue? It certainly appears to be the primary driver of circadian rhythm, but it’s not the only one. In a recent study, researchers found that while monochromatic blue light suppressed melatonin production via melanopsin stimulation, polychromatic white light (which includes blue light) stimulated melanopsin equally while suppressing melatonin to an even greater degree. Clearly, it’s not just blue light’s effect on melanopsin affecting our sleep cycles.

Still, blue light is the low-hanging fruit, and there are some simple steps you can take to mitigate its late-night effect on your sleep.

  • Keep electronics usage to a minimum or completely eliminate blue light (alarms, TVs, laptops) after dark.
  • Go to sleep earlier.
  • Use candlelight (read how a fellow MDA reader gave this a try for 30-days).
  • Keep your room as dark as possible and your sleeping quarters pitch black.
  • Install F.lux (totally free) on your computer to cut down on blue light emissions.
  • If you want to try a somewhat extreme experiment you could even wear orange safety glasses at night.

(Thanks to this thread on PaleoHacks for the last two tips.) Also, don’t forget to expose yourself to blue light during the day so that your cycle normalizes – it goes both ways, you know.

Does anyone have experience cutting out blue light exposure to great effect? Let the world know in the comments.

You want comments? We got comments:

Imagine you’re George Clooney. Take a moment to admire your grooming and wit. Okay, now imagine someone walks up to you and asks, “What’s your name?” You say, “I’m George Clooney.” Or maybe you say, “I’m the Clooninator!” You don’t say “I’m George of George Clooney Sells Movies Blog” and you certainly don’t say, “I’m Clooney Weight Loss Plan”. So while spam is technically meat, it ain’t anywhere near Primal. Please nickname yourself something your friends would call you.

  1. Thank you for posting this! Your explanation of the types of lights is so much more helpful than the typical ‘don’t sleep with the tv on…don’t keep your cell phone next to the bed’ you see in tips for a good night’s sleep articles.
    I downloaded f.lux last night and began yawning within minutes (okay, it was seconds!) and I went to bed early. Also for the first time in years, I tried and succeeded at falling asleep without the tv on. Thanks again!

    jk wrote on March 5th, 2010
  2. I also found that Vitamin B12 status matters a lot to melatonin production. (People without enough Vitamin B12 don’t make enough melatonin.) Older people often have trouble absorbing Vitamin B12.

    When I tried the methyl form of B12 (under the tongue) I started sleeping like a log! And much longer at night. The bedroom has to be really dark, of course.

    I prefer the Jarrow brand of methylcobalamin, but others no doubt are all right as well.

    Vitamin B12 also improves small muscle coordination. I read that Olympic marksmen take methyl B12 because it eliminates a tiny tremor and improves their scores.

    Here’s to good sleep!

    piano-doctor-lady wrote on March 5th, 2010
  3. Flux is SICKKKKKK Thanks mark

    frank wrote on March 5th, 2010
  4. After looking carefully at the melatonin study statistics, It seems that the sample size was extremely small: n30 to be even more convincing.

    Luke wrote on March 5th, 2010
  5. I did the candlelight thing last night – it worked SO well.

    Ryan Denner wrote on March 5th, 2010
  6. I JUST INSTALLED FLUX AND IT IS AMAZING! I seriously just spent ten minutes sitting here turning it on, turning it off, turning it on………..

    Gary-A wrote on March 5th, 2010
  7. For some strange reason, I can’t get Flux to download. I think maybe it’s our apartment complex’s firewall that I can’t get around. Can someone e-mail me the .exe file so I can install it?

    supercanid (atsign) gmail (period) com

    Thanks in advance!

    Kate wrote on March 6th, 2010
  8. I have not purchased one of these (but plan on doing so), but for those considering replacing their alarm clocks you may like this:

    It’s a “daylight” clock that simulates a sunrise, so it attempts to wake you up by assisting with serotonin production rather than with a loud noise. I really like the idea of it since I room in a basement right now, so I have no way as of current to wake to sunshine on my face. Saving for it!

    Benjamin Skipper wrote on March 6th, 2010
    • That looks expensive! Cheap people (like myself) could perhaps attach a cool-temperature (i.e. florescent, LED) light to a wall socket timer for almost the same effect.

      Cullen D. wrote on March 8th, 2010
  9. The Candlelight trick seems to work well. For more info on daily health including diet and tips see our blog.

    Matt wrote on March 6th, 2010
  10. I installed Flux but now nothing happens when I click on it (I want to change the settings) — anybody else having this problem? There are no answers on the Flux page, tho many people have also asked the same question there.

    Anne Scott wrote on March 7th, 2010
    • go to your bottom right hand icon tray and click on the icon there and see if that works.

      Jess wrote on March 7th, 2010
    • Are you using Windows or Mac?

      Hollie wrote on March 7th, 2010
  11. I’m a little confused. What is this saying specifically about incandescent bulbs? Are they considered red? Or blue? All I see mention of specifically is LED screens, TVs, etc.


    elizabeth wrote on March 7th, 2010
  12. Does this mean daytime naps are discouraged?

    Daphney wrote on March 8th, 2010
  13. Hi Mark!
    Great post as usual. This doesn’t have to do with light, but does have to do with sleep.

    I wanted to add that anyone who supplements with vitamin D should take it in the morning only

    Diana wrote on March 9th, 2010
  14. Continued from above…

    oops, I hate when I hit submit by accident!!

    Anyway, I had read, I thing on Dr B.G.’s blog (Animalpharm), only to take vit D in the morning as it simulates daytime to our bodies. (makes sense).

    Since I started supplementing in the morning only, my quality of sleep has been much better. I used to wake up after about 4 hours (around 2am,) and not be able to get back to sleep. Now it only happens occasionally, so I am trying to make the room as dark as possible, and will try to keep lights dim after sun down as well.

    One more tip- keep some water handy OUTSIDE the fridge if you wake up thirsty. I can’t tell you how many times opening the fridge door in the middle of the night woke me right up.

    Diana wrote on March 9th, 2010
  15. I’m going to try out candlelight. :)

    Noel wrote on March 10th, 2010
  16. I’ve been using F.lux and it works great! Really helps. The last few nights I’ve gotten to sleep so much better than usual, and I stay asleep instead of waking up (which I used to do a lot of).

    Hollie wrote on March 10th, 2010
  17. Can you get the orange safety goggles at a local store? Or only online?

    E.M.R wrote on March 10th, 2010
  18. Any way we can do what f.lux does to the tv?

    Matt wrote on March 10th, 2010
    • Build a HomeTheatherPC and install f.lux on that.

      Jonathan wrote on March 11th, 2010
  19. I’ve been trying the candle light approach too since reading the posting and it definitely has a calming effect. Here in northern Scotland we have very varying sunsets, due to our northerly lattitude. At the moment it is fully dark by 1830 and the first evening I just didn’t turn any lights on at all, just lit candles – I was on my own so suited myself. It felt good and the f.lux made a massive difference to my eyes.

    Since the we’ve been using minimal light for the last couple of hours before bed just using a bit more earlier in the evening to get the chores done.

    I have to say I came to the conclusion that Grok probably didn’t play Scrabble, at least not during the evening, as candlelight wasn’t really enough to see the tiles and the board properly (we have a darkish coloured set and wooden tiles!). However, my husband, not wishing to disrupt my plans silently disappeared and returned wearing his miner’s headlamp set to infrared setting, I don’t think I’ve laughed so much in years, Primal Law 7 me thinks.

    Anyhow feeling sleepy at around 10 with less lighting in the preceding hours. Now just need to work out what’s waking me around 2:30 am every night and then hourly thereafter, think it might be the emissions from my digital clock radio which although now covered isn’t switched off, doh …

    If this works we’ll need to start actually shutting our curtains to block out the daylight a couple of hours before bed time as we approach mid summer to keep some kind of pattern for sleeping.

    Kelda wrote on March 11th, 2010
  20. Re: sleep, melatonin,blue light, etc……
    check out for their authorative info and light bulbs, computer screens,et al that block blue light at nite

    Bill K wrote on March 11th, 2010
  21. “It’s all the same to our bodies, because for millions of years blue light meant daylight, not a late night blog comment section or reruns of The Daily Show.”

    Suggestion: Make a script that sets your blog to monochrome red if the reader’s browser indicates their local time is ‘night’.

    Your Future wrote on April 11th, 2010
  22. Re: using candle, kerosene et al as an alternative to the electric light bulb….

    there is a risk…..

    the output from these sources adds to the toxic load the body is subject to in our modern society…. what all they are is another subject, but when the total toxics exceeds the body’s ability to eliminate them, we come down with one of the adult-onset degenerative
    diseases, cancer among them


    Bill K wrote on April 12th, 2010
  23. the output from these sources adds to the toxic load the body is subject to in our modern society

    bilgi işlem wrote on April 30th, 2010
  24. Hi there,

    I looked over your blog and it looks really good. Do you ever do link exchanges on your blog roll? If you do, I’d like to exchange links with you.

    Let me know if you’re interested.

    forex wrote on April 30th, 2010
  25. I just can’t get to sleep early. No matter how hard I try.

    Noel - Tricycles For Adults wrote on May 9th, 2010
  26. Hi there!

    As long as i can think i have trouble getting to sleep.

    I want to exchange my normal bulbs to bulbs that are good for sleeping.
    Now i am wondering what the right bulbs are:
    – normal ‘nightlights’ in the store (has it blue light in it?)
    – LED – lights – i guess they are also blue. Red LED lights?
    – lightbulbs that are red (normal bulbs with red covers)
    – only lights from

    I find it confusing. And i am starving for info. Are there books? Is there any forum or something that talks about this? The blue-light thing is pretty unknown, is it?

    Thanks for the help!

    Mike wrote on June 19th, 2010
  27. I usually fall asleep in a few minutes in a dark environment but in a light room and with some sort of noise it takes maybe an hour for me to fall asleep.

    Molly wrote on July 25th, 2010
  28. Wow. I am now fully aware of just how much I’ve been screwing over my circadian rhythms.

    Thanks so much for your post! I was reading about circadian rhythms at two in the morning on my laptop, then wondered why I was having all those sleep problems. =D

    Brady Yoon wrote on September 16th, 2010

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