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. A few more tips I’ve found helpful:

    Peach light bulbs not only help get the blue out, but are wonderful for entertaining guests. Everyone looks better. You can also paint energy-saving flourescent bulbs with non-toxic paint from the craft store. They last for years and they’re luke warm. Try splattering the paint if it ends up too dark when coated. I’ve made “make-up” lighting for my bathroom this way (a.k.a. day (blue & pink,) evening(peach,) office (blue, green, and pink.))

    Try using plug-in timers on lamps and/or plant lights to create “F.lux” for your home.

    When I get off the computer or TV and read before bed, even with an ebook reader or cell phone, I fall asleep on time and get much better sleep. Admittedly, though, I have my ebook text set to yellow on a brown background. Intersting that!

    Lastly, I either use a loud box fan or the White Noise selection at to drown out noisy neighbors, or just for particularly sleepless nights. The pink noise is great for covering voices. The White noise is nice and reminds me of an airplane ride. The Brown is very nice at first, but strangely this and the pink keep me awake. I’d like to find a grey noise app somewhere.

    gggirlgeek wrote on June 10th, 2011
  2. Oh! you can mix the 3 types of noise at too. Just open 3 browser tabs or windows and they’ll play at the same time. I “think” this would work on the new smart phones with Adobe Flash player too. I’ll try it.

    gggirlgeek wrote on June 10th, 2011
  3. Last post. Sorry for hogging the spotlight.

    The reason I suggest all of these techy solutions is because I live in a studio apartment where I am always in the same room with my computer. The computer must stay on 24 hours because it’s my DVR, and has shows scheduled to record at all the time. So far, I can’t even sleep without the sound of the computer fans going. But you all have gotten me thinking about trying to work something else out.

    gggirlgeek wrote on June 10th, 2011
  4. I just found an orange “night mode” screen app for Android! Someone here asked about this and I’m so pleased to have found it.

    It’s called Chainfire3D. It’s actually a graphics driver which has the “Night mode” setting inside when you open it…. The bad news: You must be rooted, and you must have a very new device — 1Ghz processors only. The good news: It has several screen color options — Salmon, Red, Amber, Green and Blue. And it has a homescreen shortcut just for toggling night mode with one touch. Not only that, but it’s original purpose is to speed up your phone while playing high-end 3D games. I also plan to use the Blue screen mode during the day to see if I feel more awake.

    What an excuse to treat yourself to a new gadget! :->

    This was my last blue source of light that needed to be eliminated before bedtime. Thanks to all of the advice here I should be able to get on a regular sleep schedule now. Would not have known the value of this app without you all. Thanks again!

    gggirlgeek wrote on June 14th, 2011
  5. What about green light? My alarm clock has green digits.

    Sue wrote on June 27th, 2011
  6. It’s currently 2:14AM and I’m having trouble sleeping…again. After stumbling across this article I believe some of my sleeping problems are due to my alarm clock which displays the time in bright blue numbers. In the past I had come to believe that I fell asleep faster when facing away from my clock but in the back of my head I didn’t see any reason why this would be, however I guess that suspicion was totally correct!

    Taylor wrote on July 31st, 2011
  7. THANK YOU for the f-lux idea. I’m going to insist my 16yo daughter install on her laptop. She loves her laptop (bought it herself with her own money!) but she uses it ALL THE TIME, and it’s in her room. She has memories of being 3-4 and wondering why everyone else in the house was sleeping but her. These days, she might fall asleep by 3am. Of course, I’ve mentioned Primal/grain-thing to her, but she LOVES her grains too much. But, hopefully, adding this free little doo-dad to her laptop might have a positive effect on her sleeping.

    kimelah wrote on October 3rd, 2011
  8. 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
  9. 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
  10. 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
  11. 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
  12. 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
  13. 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
  14. 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
  15. 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
  16. 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
  17. 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
  18. 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
  19. 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
  20. 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
  21. After being diagnosed with PTSD two years ago,(also an alcoholic, mickey) I have found that a red light helps me sleep and stay calm. Im not sure why but it it reminds me of being in the belly of a submarine…a very safe place. There are still nightmares accompanied by cold sweats but when I wake and see the red light, I become calm almost immediately. Mickey, if you are still reading this, I want to bring a place called the “refuge” to your attention. They did wonders on my trauma issues!

    Scott wrote on September 27th, 2012
  22. Awesome blog you have here but I was wondering if you knew of any message boards that cover the
    same topics discussed in this article? I’d really like to be a part of online community where I can get suggestions from other experienced individuals that share the same interest. If you have any suggestions, please let me know. Thanks!

    Anagha Comar wrote on October 4th, 2012
  23. This is how I (age 79), after years of
    worsening night time sleep,am now continuously sleeping deeper and longer, and furthermore, have virtually eliminated urinary wake-ups. Originally started to deal with excruciating pain due to onset of hip arthritis, am now totally pain free following six months of “earthing”.
    For full information, go to:

    william wrote on October 4th, 2012
  24. We manufacture the lamps and glasses for the UK and European markets. Reports from customers say 68% of them using lamps or glasses can gain effective control of sleep dis-orders. The high specification products allow maximum reduction of Blue Light in the spectrum. best regards to all sufferers. Ronfell wrote on October 25th, 2012
  25. I have a cheap LED flashlight that has a red only feature, I would prefer that to a candle. Safer too. Any comments on that strategy??


    Joe wrote on November 14th, 2012
  26. has anyone ever heard about that blue light is bad for our eyes? They’ve launched special glasses blocking blue light to minimise the exposure to it during the day. So what is it now: Blue light on or off?

    Judith wrote on January 30th, 2013
  27. Thanks for sharing your thoughts. I really appreciate your efforts and I am waiting for your further write ups thanks
    once again.

    oakley store wrote on March 25th, 2013
  28. Have you heard about segmented sleep patterns? What’s your opinion on this?

    Marcos wrote on April 11th, 2013
  29. Just letting you know, there are also spectacle lenses that have “Blue Control” coatings incorporated, which filter out these blue emissions. Great option for computer users to have this option, which looks just like a normal lens.

    Carina wrote on December 4th, 2013
  30. Great post!

    Question for everyone: I work a shift from 3:00 AM – 11:00 AM. I get roughly 5 hours of sleep at night and then take a 3 hour nap in the afternoon to maintain the number of hours. I’ve recently picked up a pair of blue blocking glasses to use at night to try to optimize my melatonin production at night for those solid 5 hours. Should I continue to wear them for the early morning hours (3:00 AM until sunrise) where it is still dark or use regular light to wake myself up and halt melatonin production?


    Ken wrote on April 24th, 2014
  31. I have a problem that if I do not read before sleep I can not fall asleep and therefore need to use a led light for reading in my bed. If I do not.. I can be in the dark for hours and I won’t get any sleep at all and mess up my cycle that way.

    The Ixian wrote on July 7th, 2014
  32. Yes! This is actually a big issue btwn my wife and I. She says she needs to have noise on in order to go to sleep and usually its a netflix show on our computer. Before we met I never used any tv or radio or anything to help me fall asleep and I feel like I never get a good night’s sleep. I tried to show her articles about this very subject but she’s very stubborn and tried to claim that since it wasn’t the television but the computer, that it was ok. I don’t know what to do bc I do believe her that she needs the background noise to go to sleep but I also believe this is bc she’s trained herself to fall asleep to this noise and that if she could wean herself off this habit, she’d sleep better. She literally wants to have close to 10 hours of sleep a night and I honestly think its bc she doesn’t have good sleep bc the computer is on playing a show. I hate having these shows on in the background when I sleep. Any ideas of what to do? Eventually the computer does go into sleep mode, so its not like we have the blue light on all night. But I still feel like this is messing up our sleep.

    James wrote on August 29th, 2014
  33. How can I save “ALL” this stuff? mind blowing to say the least??Thanks,,Cliff Gant(inventor)

    cliff wrote on August 30th, 2014
  34. I have tried f.lux on my hand held devices, but on my multi screen PC’s I have found a new program pc sun screen to work really well. You can even change the time when you want to sleep as well as many other things.

    chris hunt wrote on October 28th, 2014
  35. * For computers, there is software that adjusts the screen colors automatically to the time of day or room you are in. This one is free for Windows:
    * For Android phones, you can use blue light filter for eye care:
    * There is preventative eyewear that can be purchased in a yellow tint or clear tint usually from websites such as or
    * And finally, I found this article that gives some recommendations on how to protect your vision:

    Panes wrote on November 5th, 2014
  36. I designed and implemented accent lighting forb use as general lighting, and limit the brighter room lighting for those occasional necessities. Since the only cool-white light inb use is the porch light, I don’t have much in the way of blue light impact. Yet, I still have issues retaining a dawn to dusk waking cycle. Point is, not everyone has the day-awake abilities. Some of us are cursed to sleep at night. Also, I have issues seeing red, but that is for another conversation.

    Willy-bill wrote on November 27th, 2014
  37. Can you… *sigh* can you willpower through blue light’s inhibitive effect on melatonin production and just “go to sleep anyway” because that’s “what [you] want to do”? Someone I know said they don’t know why they can’t get on a normal schedule, I said start with cutting electronics for an hour before bed cause that works for me, and pointed to blue light. They said–you know what, I give up. I give up on this person twice as hard as they have given up on science.

    This person can figure it out on their own.

    Taylor wrote on January 12th, 2015
  38. REM – I’m surprised no one has mentioned it in reference to this (excellent) article. From what I understand, each time you enter the REM stage throughout your sleep, it lasts longer and longer, and it’s the final stage, closest to waking up, that REM is the longest and deepest. (I won’t take the time here to explain the importance of REM on our overall health and well-being, and the consequences of not getting enough of it, but it is worth looking into for everyone, whether you have sleep issues or not.) When you are exposed to light in between the REM stages, the pineal gland resets and your REM cycle starts over, so you never reach the most important phase of REM. (Red light has no effect on the REM cycle, blue has the most effect.) Many people complain that they’re always tired, even though they got a full night’s sleep. This is because you will never be totally rested without a sufficient amount of REM sleep. Several years ago I started blacking out my bedroom window and turning all nightlights off before going to bed. If I need to use the bathroom in the middle of the night, I do so with my eyes closed, so that the light from the glass block window in my bathroom doesn’t disturb my pineal. That sounds so weird lol, but it is working so well. I do go to sleep watching some mundane show on my laptop, but I turn the screen brightness all the way down, and it goes into sleep mode automatically, so if I wake up during the night it is not giving off any light. Just before my alarm goes off in the morning, a bright fluorescent light that is plugged into a timer turns on, which simulates morning and gently nudges me out of deep sleep. One of the best things I’ve done is buying a talking alarm clock. It drives me crazy not knowing what time it is if I wake up during the night, so now I can press a button and the clock tells me the time, without exposing me to any light. It’s a little one on a keychain, it has an alarm, it was very inexpensive, and it has worked wonders. Amazon sells several styles. After reading this article, I will now pay more attention to the evening hours before going to bed. I will also make sure I get plenty of “blue” light during the day, and hopefully both my REM cycle and my circadian rhythm will be operating at optimal levels, making me even more happy, healthy and energetic. :-)

    Gramma Kaye wrote on March 30th, 2015
  39. Just installed F.lux. Love it!

    Gramma Kaye wrote on March 30th, 2015
  40. [NO JOKE] When I can buy a gas lamp from? :)

    Anca wrote on July 31st, 2015

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