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. Talk about counterproductive! who knows if this picture is accurate, but the “glow points” in this supposed sleep mask appear to glow blue. Yikes.

    joey wrote on November 19th, 2011
  2. I enjoyed this article and all the comments and posts. I’ve been basically primal for 4 years but I am SCREWED because I work nights. Always have (tech support, we’re talking the bulk of 20 years) so I cannot implement most of these wonderful suggestions. I’ve studied circadian cycles, shift work, etc., and am doing the best that I can. I have a very dark room, take melatonin before going to bed, take my supplements when I get up, and sleep very well during the day. I think I am one of those nocturnal people who were sent to protect the others during the day because being up at night is so natural for me. Whenever I have to come into work during the day for training, etc., it’s miserable and so hard to stay awake, but I am fully awake all night without caffeine or drugs. But am I *really* an anomoly? While my health (other than asthma/allergies) is close to perfect (you should see my blood counts!) I’ve gained 12 pounds or so this year that will not come off though I have not changed my eating habits, etc. When I’ve written to other primal “gurus” I am dismissed with “quit working nights” like it’s that simple. For one thing, I love the benefits of working nights, not the least of which is the shift differential that goes along with it; after losing a comfortable job I held for 20 years I’m stuck starting over again so I’m making the most of where I’m relegated presently. So am I doomed to never have the best health I could because I am a night owl? Or am I already there (since being a day person is so foreign)? I have even thought about taking a day shift to see if that would help me drop these pounds (I stayed in my 5# range for 3 years) but I can’t afford the pay cut so that’s not an option at this time. I am actively looking for another job and am open to working days though I know my mindset is not ready for it. But my motto is “If you continue to do what you’ve always done, you’ll continue to get what you’ve always gotten” (and yes, I sell that on a t-shirt!) so if I can afford to change shifts, perhaps I will. Thanks for reading.

    Trisha wrote on November 29th, 2011
  3. This is bull crap. I have been sleeping with a light on since I was born, and I don’t ever have a problem. If you condition your body at a young age it will get used to how you sleep, with light or not. Obviously if you sleep with light off the entire time your alive, it would be difficult to get used to light on. For me, I find it extremely difficult to sleep with light off. I constantly wake up. It’s the same effects for people towards light on, just this time, it’s off.

    purplefinch wrote on January 17th, 2012
  4. After having sleep problems for over a year, I read about the circadian rhythm, blue-sensitive ganglion cells and reading about every blue blocking device around, I ended up with the glasses.
    As I have a family, I didn’t want to use blue lights as it would affect everyone and candles are too dangerous with kids around. I tried commercial sunglasses, but blue objects still look blue so they weren’t very effective.
    In the end I made my own which worked well for me. After about 30 mins I could feel myself relaxing. By bed time I was ready for a good kip.
    I’ve made 50 pairs of these as cheap as I could and am selling them on eBay at a VERY low price here:

    If they go well I’ll make more. If they don’t I’ll drink beer and watch the telly like normal people :-)
    Best of luck


    Steve wrote on March 6th, 2012
  5. Guess shift workers don’t fit into your precise plan. While I agree there’s a needed importance in quality of sleep, the comments appear to make this overly complicated system just to get a natural sleep.

    L wrote on March 7th, 2012
  6. 301 Moved Permanently I was suggested this blog by my cousin. I’m not sure whether this post is written by him as no one else know such detailed about my problem. You are incredible! Thanks! your article about 301 Moved PermanentlyBest Regards Lisa

    cimengse wrote on March 16th, 2012
  7. I like the helpful info you supply to your articles. I will bookmark your blog and test again right here frequently. I’m rather sure I will learn a lot of new stuff right right here! Best of luck for the next!

    GGG wrote on April 9th, 2012
  8. I’ve had chronic insomnia for the last few years. It has been so severe that I spent hundreds of dollars seeing family doctors and even a psychiatrist. All the professionals threw prescription after prescription at me- sleeping pills, anti-anxiety meds, etc. You name it, I’ve tried it. I don’t even sleep with the sleeping pills. It has been so depressing and discouraging. I’ve followed all the right procedures recommended for good sleep hygiene. Don’t use any caffiene, exercise a lot during the day,…. I have been looking and re-examining why this came to such an ugly head about 3 years ago. I was about to be laid off from a job I loved for 17 years so I accepted that it WAS anxiety. But after reading your article and the comments, I have gone back and discovered that about that time, we bought a large flat screen tv. I do try to read before bed as opposed to watching tv since I was aware that could be an issue. But I have been reading in the same room while my husband has the tv on. I’m now experimenting that perhaps it is the blue lights from the tv? I read the comments and ordered a cheap pair of blublocker glasses and will use that as well. Can anyone tell me if there would be a difference in the amount of blue light from a large flat screen tv versus our old small tube tv?? Thanks for your article and all these comments and suggestions. I pray that this is the answer to my insomnia and that I can get off these horrible pills and their side effects. Thanks again.

    Shirley wrote on April 16th, 2012
  9. Can anyone recommend a blue blocking sunglass or eyeglasses. I’ve researched on-line and there are several companies and choices. Still, I would like to buy eyeglasses/sunglasses that someone has found to be very effective- I don’t care about style either! I want what works!! Thanks!

    Shirley wrote on April 16th, 2012
  10. I have a Himalayan salt lamp that softly lights up the open plan kitchen dining and lounge till I can get candle holders to put on the wall, safely out of harms way. It is great when we get up in the middle of the night for a glass of water.

    There are all sorts of beautiful ones that look like works of art that use tea light candles which are pretty safe in the glass holders.

    Or better yet backed with a mirror to reflect the light back into the room therefore needing less candles.

    Jo-Anne wrote on June 6th, 2012
  11. I found anti-blue light glasses at an optician the other day and bought one. Does anybody know how effective they are to you?

    Khon Lanna wrote on June 20th, 2012
  12. Hi Mark,

    I’m doing research on how blue light affects sleep for my blog ( and found this website. Wow, I’m really impressed with your writing. Thanks for all of the good info. Maybe we can collaborate some day. Maria

    Maria wrote on August 22nd, 2012
  13. I am a TV repair Tech, my client told me about a study a university did on the subject of watching anything with a flourecent light including lcd tvs (but that was due to the flicker rate of them which is very fast and I dont see how that could be an issue) But, It lead me to your article, great write up! Do you think adjusting the tv’s warmth of picture would help those who just love to watch tv in bed ?( movie mode usually reduces blue output, makes all the white colors more tan )

    Dean Wysocki wrote on August 27th, 2012

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