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. Candlelight is a good idea. And my wife will like the new romantic atmosphere….

    Organic Gabe wrote on March 4th, 2010
    • Just be safe… candles and unattended cooking are the top two causes of house fires.

      animal (ex-firefighter) wrote on March 4th, 2010
      • Yes, good advice. My concern is not an unattended candle so much as it is our cat walking by it and catches its tail on fire, jumps off the counter and dashes into the curtains.

        But I do love the candle idea, and my wife has a huge collection of them. Now that I’m ready to experiment with candle light at night, we’ll have an amalgamation of senses that include vanilla, cinnamon, wild berry, velvet, lavender, and midnight jasmine.

        Can an aroma ambush stimulate the sympathetic nervous system?

        Johnny at The Lean Saloon wrote on March 4th, 2010
        • re: cat’s tail knocking it off and/or curtains – that’s why I’ve started buying/acquiring on-the-wall candle holders that hold the candle INSIDE it, in a glass jar.

          Also, I only use beeswax candles. I love the smell, and it’s NOT petroleum.

          kimelah wrote on October 3rd, 2011
      • poor electrical work is the top cause of house fires

        john wrote on January 5th, 2011
    • I love the candlelight idea. And even if it is artificial light…. if you use only a few candles then the amount of light that is produced is significantly lower then the amount of light that is produced with several lightbulbs and a glaring TV, computer, or whatever.

      When the sun goes down, our body naturally begins to go into sleep mode. It may take a couple of hours, but when its pitch black its sleep time!

      Todd wrote on March 4th, 2010
      • Candle light does not allow a person to do anything. Wash the dishes? Read? Take a shower? Please.

        I used to use kerosene lamps back in the 60s, but probably they emit poison gases. And if you turn them up high enough to read, they smoke up the chimney. And the room. And the smoke keeps the light from coming through. But it is a warm (not blue) light.

        Even so, unless we are to retire when it gets dark, we will be using electric lights. In northern areas, it gets dark in winter at 5 pm.

        I wonder about the melatonin-sleep-blue light matter for people who live in the far north where it can be light for 24 hours. Anyone?

        docbets wrote on March 10th, 2010
        • “unless we are to retire when it gets dark, electric lights”
          Electric yes. But we can more wisely choose which ones. Don’t buy the 6500K bulbs for night time use.
          I’ve got a lamp with two independent sockets/switches. A regular bulb in one and a 60watt equivalent florescent yellow “bug” light in the other so I can choose which to light depending on the time. The bug light is more than enough to read or do anything by. My 2 year old daughter cried wanting to go to bed the first night we tried it and has stopped fighting to stay up later. Last night we had a birthday party and used the normal lights and she didn’t sleep well and woke up at midnight and was up for a good while.

          Jonathan wrote on March 11th, 2010
        • Wash the dishes? Check. If you’re meticulous, you could do it with your eyes closed.

          Read? CHECK. People used to read under candlelight all the time. It’s totally sufficient.

          Take a shower? Check. I always shower with the lights out, actually. I can’t imagine why you’d think it would be a problem.

          fgd wrote on November 4th, 2012
        • I frequently bathe with 2 dinner candles lit, and can easily read by those whilst taking a long bubbly soak. This began by being annoyed by the automatic vent system in my bathroom that turned on with the light, it was too annoying to read with that on.

          I imagine if one is careful one could easily wash dishes by candlelight; I always put sharp knives off to the left in the sink, so that even under suds I know where they are, move the hands slowly that’s all!

          I mean, how do completely blind people wash their dishes? Carefully! (please don’t say they let the guide dog lick the plate & then put it back lol!)

          Tanya wrote on August 16th, 2016
    • I totally agree with this. People have no idea what they are doing to their bodies and will die accordingly.

      WG Newman wrote on July 20th, 2011
    • I sleep with a black lite on my 1960 posters in my bedroom . I sleep like a log.

      JL wrote on November 26th, 2012
    • There is preventative blue light screen protector that can be purchased usually from websites such as

      Jackie wrote on January 25th, 2015
  2. “zeitgeber” time giver… if my german is correct. They come up with some marvelous compound words.

    Peggy wrote on March 4th, 2010
    • Yes, literally it’s “time giver” but it means “timer” :) Makes sense!

      Annette wrote on March 4th, 2010
  3. Very interesting! I will be interested to hear all of the comments on this.

    When I read “Lights Out” several years ago, I wondered about fire at night, moonlight, bright stars etc., and why they wouldn’t have disrupted melatonin in Grok’s time. Maybe the blue light theory explains this??

    Also, “Lights Out” mentioned that just a small amount of light from a fiberoptic scope shined on the back of a knee was enough to cause problems, so apparently it isn’t just receptors in the eyes that matter.

    Lastly, I am wondering how latitude affects melatonin comparing someone on the equator to an Alaska native? Do people just adapt to their environment or is a genetic component more important here?

    Rodney wrote on March 4th, 2010
  4. With the insanity of Facebook status updates (for all the self-important people) and twitter being logged in every few nanoseconds, staying away from an electronic device seems impossible for the tech-crazy Gen-X. Just go to any mall in America and looks at the teens, muffin tops busy on their cell phones. No to mention teenage boys castrating themselves with radiation from cell phones and frying their testicles with video games and not making any testosterone. Pretty soon, they would all be sitting and wathcing Oprah eating tofu burgers (or maybe they are).

    Kishore wrote on March 4th, 2010
    • re: electronic devices, cell phones, etc.: You nailed it! Even though there is ample evidence that prolonged up-close cell phone use can create tumors, half the population seems to have a cell phone stuck to the side of the head (with crazy glue?). “Darwin Award” candidates abound, so hopefully the situation will prove to be self-regulating. (Says he, typing this message on his laptop… 😉 )

      Dr. Surf wrote on July 22nd, 2011
      • There is no ample proof that cell phones cause tumours or any type of cancer.

        If this was the case wouldn’t we see the rate of tumours increase.

        It’s common knowledge that heat will reduce sperm production, however if you wear briefs you are just as likely to reduce your sperm count….

        Row wrote on July 22nd, 2012
  5. I have bipolar disorder and it used to really wreak havoc with my sleep cycle, until I started wearing copper safety glasses after 6pm and a sleep mask at night.

    The glasses were a huge pain to get used to (and the sleep mask took time too), but it made a big difference. During the winter, I also use a lightbox for about 20 to 30 minutes every morning. This has pretty much completely normalized my sleeping routine and my energy levels. Incidentally, other bipolar symptoms are also much easier to manage and I seem to be in “remission” (symptom free) much of the time.

    It’s worth a shot for people having sleep issues.

    Username wrote on March 4th, 2010
    • Hello — I see that you are one of millions that have bought into a label of “bipolar” disorder
      Only YOU know you — being labeled with a “disease” that can not be actually proved through ANY scientific method begs the question? Is this a disease or not I recommend you look at this – only if you are interested in answers

      Lynda wrote on March 4th, 2010
      • I think this is a rather sharp response. I will go and read your link, but I would say this. My grandmother was treated for, what was known then as ‘manic depression’ through her early adulthood onwards, this included EST, not something I would wish on anyone. She died age 56 from complications of uncontrolled diabetes. I was insulin resistant during two pregnancies so although not considered diabetic non gestationally clearly have a predisposition to metabolic sensitivity.

        The fact that I have hugely benefited from insulin control through Primal eating and have, for many years worked with swings that are outwith what is considered ‘normal’ that are now normalising I don’t think it unreasonable to consider there may be a link. I have only recently been open about this. Unless you have lived through (or alongside someone) in a manic epsiode I don’t think it is fair to say it’s buying into a label.

        Kelda wrote on March 5th, 2010
        • I’ve just followed your link – I do not take any form of drug, I have never followed the CW on this, in fact following the history of my Grandmother’s treatment from CW (which was effectively to foreshorten her life) my family ensured I was never seen by the ‘establishment’. I have worked with an altenative thrapist at a cognitive level, not with any form of drug and have ‘learned’ my way through it. Keeping insulin low on Primal has been THE most effective ‘treatment’.

          Kelda wrote on March 5th, 2010
        • I am a rehab counselor for folks with dual diagnosis–meaning they have substance abuse issues and a “mental illness.” First, I want to say that I respect you and your family’s decision to forego any pharmacological interventions. I think it would be tempting to follow the CW and its promises of miracle cures.

          While I do believe that mental illness does occur, I wish I had the freedom to experiment with nutritional and lifestyle treatments. It sounds like you have experienced some good success by changing your habits!

          I personally have complaints about the convergence of the psychiatric and psychological fields. Psychiatry attempts to frame mental illness as a medical disorder, and as such approaches conditions from a very cut-and-dry, dualistic framework. I think that approach is what Lynda refers to (though I am inclined to agree that the comment is unneccesarily cutting). But, in my observation, you have a very valid point that there is definitely something going on with mania/depression/etc.

          I wish you the best in your continued recovery, and I sincerely hope that some day we can get real, valid science which questions the efficacy of medications, nutritional intake, lifestyle choices, etc.

          Mickey wrote on March 6th, 2010
        • Mickey (I hope this posts appears below yours)

          Thank you very much for your comment. It takes a great deal of bravery for many like Username above to speak more openly about this and it’s great to read a sympathetic post.

          I too passionately hope that further, proper, investigation of the effect of nutrition on a whole myriad of modern ‘conditions’ begins to pick up speed, from what I see around me the long term healthy survival of our species may well depend upon it.

          Since beginning this journey after a chance encounter with a guy on a ferry back from Spain (I kid you not) last November who impressed upon me the necessity of reading Gary Taubes Diet Delusion I’ve become increasingly convinced that a whole host of problems can be avoided – I think now about how many schools, clean water wells etc the money released from treating these illnesses would be released if the powers that be started to take note of what communities like this are discovering for themselves and trying hard to get CW to acknowledge.

          On with the crusade!

          Kelda wrote on March 6th, 2010
        • Don’t you love it when people who don’t have the problem ridicule you for having it? Don’t let Lynda’s smug criticism get to you. The internet is, unfortunately, a haven for the self-anointed. In fact, such people may (or may not) be partially correct, but they pollute their message because they can’t resist telling you how cool they are and, in contrast, how dumb you are. Which would seem to indicate a personality disorder. (Unless, of course, you don’t “buy into” the concept of personality disorders.)

          Diogenes wrote on July 22nd, 2011
      • Gee, Lynda, I wonder which segment of BigPharma Avicenna was working for when he described manic depressive psychosis in the 11th century. Who was Soranus of Ephesus in the 2nd century working for? The conspiracy goes back centuries!

        Ordinarily I avoid responding to comments where all capitals are used. However, the stigma of bipolar disorder is bad enough without additional counterproductive suggestions that a syndrome that occurs in all countries and devastates many lives is imaginary.

        Justine wrote on January 18th, 2012
    • I too have bipolar disorder, I have lived at 57 north (northern Scotland) for the last 10 years. During our longest days it never really gets dark – you could read a newspaper in the garden at 2 am – and during the winter we only have about 6 hours of true daylight. This played havoc with me for the first few months (I arrived in August). Once I started using an eyeblind it helped a bit.

      However, what has really helped with the bipolar symptoms is turning Primal, in November last year, since Christmas I’ve seen a huge improvement, a totally unexpected bonus and I’m beginning to suspect there is a bio-chemical link between bipolar disorder and insulin sensitivity.

      Maybe Mark 😉 will come along with a bit more info on this one!

      Kelda wrote on March 5th, 2010
      • When my blood sugar is on the way down from a high (not anymore since I’ve cut the carbs), I would get so irritable and mad at every little thing including myself. Blood sugar has a HUGH effect on mood.

        Jonathan wrote on March 5th, 2010
      • I too lived at 57N for nine years and I always had trouble sleeping during the height of summer. In the middle of June it never got darker than twilight the whole night (been at midnight) and even during the winter where it gets dark very early, the full moon sometimes made the skies barely darker than in summer!

        R wrote on April 24th, 2015
  6. Holy crap, this could explain why I have so much trouble falling asleep in my college dorm: I have a nice dark loft, but my alarm clock is this bright blue monstrosity. I find I need an alarm clock because using my cell phone just does not cut it. Should I just settle for one of those red LED’s or does anyone know of any better options?

    Nic wrote on March 4th, 2010
    • I bought a battery powered clock that only lights up when you tilt it. It’s nice not having red, glaring numbers in my face all night. And if I need to know what time it is at night, I can easily find out. It also has an alarm clock, but I have a two year old that wakes me instead.

      Wendy wrote on March 4th, 2010
      • What kind of battery powered clock do you have? I need to get a new one for my husband and have searched but can’t find one that tilts to light up. Only ones that are on continuously which I do not want.


        Susan wrote on October 30th, 2011
    • You could also go old-school and get an analog alarm clock that rings a bell when it’s time to wake up.

      Matt wrote on March 4th, 2010
    • I remember reading a while ago about an alarm clock that you wear on your wrist like a watch. You set it to a time range that you want to get up and it detects when you’re in the lightest phase of sleep during that time and wakes you then. Supposedly it’s less stressful than being woken from a deeper sleep, which makes sense I guess. Can’t remember the name of it, sorry, but could try googling it. Not cheap though, as I recall.

      LV wrote on March 5th, 2010
      • It’s called the “sleeptracker” and I have an older one. It works very well and I wake from a nice light sleep. Gone are the days where I am wioken up right in the middle of a deep sleep and spend the rest of the morning grumpy and tired.

        Real wrote on March 5th, 2010
      • Or if you have an iPhone you can download an app for 99 cents that does the same thing and includes a chart of your sleep every night. The iPhone contains the same movement detecting hardware as that watch, you are essentially just downloading the software. Top app in several
        countries. Sleep Cycle

        Ryan wrote on March 5th, 2010
    • I just cover the face of my alarm clock with a heavy towel or washcloth. Works great!

      Tami wrote on March 5th, 2010
    • My alarm clock has red numbers, but I put it on a low shelf next to the bed, almost on the floor. If I want to see the time, I have to prop up on an elbow and look down at it.

      And I never set the alarm. I use a lamp with a 60 watt incandescent bulb on the far side of the room, with a lamp timer to turn it on and off.

      piano-doctor-lady wrote on March 5th, 2010
    • I have an alarm clock/ cd player & an iPod dock by my bed, both with bright blue displays. I bought some cheap red photographer’s gel samples & overlaid them on the light-emitting areas. Amazing difference! Now I can have my sounds & sound sleep too!

      paleo-curious wrote on October 4th, 2012
  7. This really explains why I have a harder time sleeping (generally) when my cell phone is face up on my nightstand, it constantly emits a low light. How weird.

    Mike wrote on March 4th, 2010
  8. Hmmm…I might have to ditch the alarm clock I got for Christmas with huge, bright blue numbers on it.

    Shane wrote on March 4th, 2010
  9. i believe in this so strongly! so much so that after it gets dark, i put the laptop away and dim the lights in my living room until it’s my “bed time” my bedroom has no light in it and it’s a perfect sanctuary! i also feel like i’m one of the few who do not have a tv in there. the bedroom is NOT a tv room, it’s your place of rest!

    misathemeb wrote on March 4th, 2010
    • misa we don’t have a TV in our bedroom either, and likely never will! We’ve talked about it a few times, and have already decided that one TV in the house is enough.

      hannahc wrote on March 5th, 2010
    • thats cuz ur poor and cant afford more than one , get a better job pussy

      poo wrote on September 29th, 2011
      • anybody got a cookie for the troll LOL

        berian wrote on December 6th, 2011
  10. Years ago, I read about the glowing numbers on alarm clocks disturbing sleep, so I have since turned the clock away from me at night time, and it really does make a huge difference. BTW, having even dim light on during sleep has also been proven to be detrimental to long-term eyesight.

    Michelle wrote on March 4th, 2010
    • Really? Do you have a cite for that? I do not believe that dim light during sleep has ever been proven to be detrimental to long-term eyesight.

      Jack wrote on March 4th, 2010
    • Problem with all these electronics, though, especially turned around to the back, is the EMFs they emit. Those will disturb sleep a lot.

      I use a windup alarm clock, Big Ben. And if we were really getting enough sleep to begin with, we would not need an alarm clock to wake up at all.

      I have read that the way to resume getting proper amounts of sleep is to sleep til you wake up – usually people have to use vacation for this – and keep doing that until the sleep debt is paid off. Eventually, a person will wake up earlier, more in line with daylight, as the post above indicates.

      docbets wrote on March 10th, 2010
      • yes, if we’re awaken up by any external forces (alarm clock, phone ring), then we really don’t get enough sleep.

        sleep is a weird thing that we can only pay debt; we can’t store it when we’re not sleepy & withdrawl it later, like food & drink.

        but sleep until naturally wake up does work for people who have DSPS tho.


        PHK wrote on March 10th, 2010
  11. So what if I change all my lights in my house for those yellow/orange “bug” lights of a lower wattage?

    Jonathan wrote on March 4th, 2010
    • I don’t think you’ll have to do that. I picked up some 13 watt “whirlie” bulbs which said they were “soft white.” Really, they’re yellower than an incandescent bulb. Equivalent to a 60 watt. I put one in the reading lamp over my bed last night, and was very struck with the difference. I thought it would be too dim, but I read a book without trouble by it.

      piano-doctor-lady wrote on March 5th, 2010
      • I forgot to mention something else.

        In the kitchen, I have deep yellow walls between the cabinets and the counters. I just bought “rope lights”, which are quite yellow, and I’m mounting them under the cabinets, one rope on each side of the sink. In the evening, they give enough light to putter around, and to have a background to the TV, but the room is bathed in a dim yellow glow, very soothing.

        I may try getting one of those orange TV filters as well. The rope lights draw 8 watts apiece. They were intended to be Christmas lights, so they plug right into house current.

        piano-doctor-lady wrote on March 5th, 2010
  12. It’s funny, but since starting PB 14 days ago I’ve been going by a “lights out” policy after dark, and it’s helped my sleep immesurably. I was just doing this intuitively. When I get home at night, I only turn on the lights I need for a specific task, like washing the dishes, or cooking something, or a small reading lamp to read. I websurf in the dark (probably not the best thing ever) and now have no trouble falling asleep. Before I would have to take melatonin or lie awake for hours. The change has been very dramatic!

    DarthFriendly wrote on March 4th, 2010
  13. When I saw this headline I immediately scrolled down the page to see if you had mentioned F.lux. I can’t endorse F.lux strongly enough. It has had a huge impact on my quality of life since I installed it.

    Matt wrote on March 4th, 2010
    • I installed f.lux yesterday after reading the article!

      Yesterday evening, for the first time in living memory, I spent a couple of hours on the computer, and by 9:30 p.m. I was bored with the computer and wanted to curl up with a good book in bed. By 10:00 I was ready to turn out the light. I had read years ago in “Lights Out” that sleep before midnight is worth much more than sleep after it, but never was able to get to sleep until almost midnight.

      This f.lux program is WIZARD! Mark gets a real vote of thanks for mentioning it!

      I’ve also decided not to watch TV after dark except on Saturday night. And I changed the reading light above my bed for a “soft white” compact fluorescent, yellower than an incandescent bulb.

      piano-doctor-lady wrote on March 5th, 2010
  14. It’s great to see some recognition for the importance of circadian rhythms. I did my MS in a circadian physiology lab, and am now doing my PhD work next door to the guy who discovered melanopsin. Light is very important (but you have to take the light intensity WAY down to make a significant difference), but you would be shocked at how much feeding patterns can play into sleep cycles as well. Even subtle fluctuations in temperature can make a big difference. Of course, it is mostly impractical for the average human to take those things into daily consideration.

    Justin wrote on March 4th, 2010
    • Justin,

      Can you provide more information about issues that affect sleep? It sounds like you are working right next to a world class researcher and aren’t doing shabby yourself! We should take advantage of this. Everyone here is jumping into changing lightbulbs… and no one replied to your post.

      Can you provide more detailed responses to Mark’s article? Are there other ways to get better sleep? etc.


      Logi wrote on March 8th, 2010
  15. One sleep related word that I really like is Suprachiasmatic Nuclei, or SCN for short. That’s the region that is taking all the light waves in and telling your brain to either take a break or wake up.

    rtegan wrote on March 4th, 2010
  16. As far as orange glasses go, here is an alternative site:

    Luke wrote on March 4th, 2010
  17. Fascinating stuff Mark. I always love the variety you bring to MDA!

    For a long time I have been strict on keeping light levels low at night – I’m really sensitive to it and thought I just had paper eyelids or something. When I’m sleeping in a new room, I always have to cover LEDs if I cannot turn them off. I think some of it is psychological, because then I can relax but you have given us the sciene behind it!

    I even have 2 pairs of curtains in my bedroom to try and block the streetlight. I have slept in blackedout rooms before though and the lack of natural light in the morning just makes you feel groggy! So some light is good to wake your body naturally and gradually :)

    Luke M-Davies wrote on March 4th, 2010
  18. What about the lunar cycle? Some people think that it’s good to expose yourself to varying degrees of moonlight, as ancient people were. It’s supposed to regulate your menstrual cycle if you have one. I can’t really block out all the outside light when I’m in my city bedroom, but in the country I can. Still, in the country, moonlight streams in on some nights.

    shannon wrote on March 4th, 2010
  19. I know when I dont get enough sleep (especially if i accidently leave my laptop in the bedroom and the charging light is going on the whole night) I get super grumpy! Now ill try to cover all lights in my bedroom, lets see if it helps.

    Athena wrote on March 4th, 2010
  20. thanks for the link f.lux!! i just installed it cant wait to see it work around 9pmish, although i plan on being in bed close to then. i was reading a few excerpts from the book lights out, which i ordered online yesterday along with a copy of mark’s book (finally), and the vegetarian myth. 40 bucks delivered for 3 books what a bargain! ill never shop at b&n again, went in and they didnt have any of the 3. in fact vegetarian myth didnt even show up in their computer search!
    anyways i was very happy to find this as the blog of the day here!

    shastagirl wrote on March 4th, 2010
  21. Sleep is incredibly important to our overall health. I agree with the idea that artificial light may be as bad as artificial foods.

    One of my goals in life is to find a community that mandates all lights out at night besides candle/fire light. There is a place in New Zealand that is like this. The stargazing must be absolutely amazing.

    CraigBC wrote on March 4th, 2010
  22. Great entry! I would add that it’s not just the blue light but also the electromagnetic radiation that can disrupt sleep –never mind all the other things it’s doing to our bodies.

    MicheleQ wrote on March 4th, 2010
  23. My husband and I have been wearing ‘Blue Blockers’ for two weeks now – starting around 8 pm. Now they’re not the coolest looking things in the world, but the effect on our bodies and minds is incredible. We start to ‘shut down’ within a half hour of wearing them. F.lux – as great as it is – matters even less because I suddenly can’t muster the energy to look at the computer any longer. Where we were once night dwellers, never getting in bed before 12, we are now solidly asleep by 10 every night. Great, timely post Mark!

    Ms. S wrote on March 4th, 2010
    • In fact it was my (the husband) comment on Paleohacks that had the link to the orange safety glasses.

      I have to say I wouldn’t be caught dead outside the house with the glasses on and avoid standing near our windows where our neighbors could see us while donning them. They have more stylish, and more expensive, blue blocking glasses at

      The effect the glasses produce is very dramatic. It was definitely worth the $10 just to experience it.

      Mr S. wrote on March 4th, 2010
  24. This line is very interesting: “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.” When hanging out around a fire (at my buddy’s ranch for example – a huge bonfire), it’s relaxing, mesmerizing, and therapeutic. Maybe the reddish color of the fire has more to do with it than we ever imagined. Very cool and interesting info.

    Sterling wrote on March 4th, 2010
  25. I downloaded F.lux and it should activate in about 20 minutes here. I also found that an old pair of cycling glasses have an orange lens I can use in place of the regular one, so I am re-activating those glasses just to see what happens.

    I wonder if F.lux helps at all if you are still exposed to tv, and regular lighting in the evening, but don’t have any special glasses on? It just seems too easy to get 95% of this right and have the 5% I miss negate all of my efforts.

    Rodney wrote on March 4th, 2010
    • Before we got our safety glasses I tried a pair of regular sunglasses I own that have a orange/amber hue. They didn’t really have any effect.

      I bought those glasses Mark linked to because I came across them here while reading up on the effects of blue light:

      Also, you can see they are the same as the pair in the pic at even though that site doesn’t sell them.

      When put these on things that are very blue appear almost black because they block a large percentage of the blue light.

      My understanding is that few minutes of artificial light can negate the effect. I haven’t experimented with wearing the glasses for a while and then taking them off, though.

      Mr. S. wrote on March 4th, 2010
    • I think you guys are over-complicating it. Just turn blue-light emitting stuff OFF when you want to go to bed!

      fixed gear wrote on March 10th, 2010
  26. I read Lights Out several years ago and have always been concerned about all those appliances with lights emanating out of them. I am now living alone after several years and it is so difficult for me to sleep in a pitch black room, I start hearing all kinds of wierd noises, but I know when I do turn the lights off and the computer off, turn my alarm clock around and my cell phone off I feel better. When I don’t get enough sleep I am like another much older and decrepit person. I am definitely trying some of the items mentioned.

    thecarla wrote on March 4th, 2010
    • Try a fan in the room. It will cover the creaky house noises.

      Jonathan wrote on March 5th, 2010
  27. Last month (partly to keep the cold out) I took a very heavy very dark colored blanket (not very decorative) to cover the windows in my bedroom.

    Since doing so, I sleep better because the room is pitch black. I also noticed that I sleep longer on the weekends averaging 8-9 hours instead of 5-7.

    Also, every night, my phone shuts down at 10pm which is my bedtime so I won’t get the annoying text from someone who really has nothing to text about.

    Pamela wrote on March 4th, 2010
    • If you cover all the windows so it’s pitch black, how do you ever wake up?? Don’t you need that sunlight coming in? If my room was truly pitch black I think I’d sleep till noon.

      fixed gear wrote on March 10th, 2010
  28. Is there anything like f.lux for room lights?

    Candles are not a practical long run solution for me, and I’m concerned about the fire risk as well as indoor air pollution. Going with no artificial light would be ideal, but it’s difficult to wrap everything up by sundown, especially when there are others in the house.

    Therefore, if there were a way to automatically switch all overhead lights to ‘red mode’ after sundown, it would be an easy way to correct melatonin deficiency.

    Jon wrote on March 4th, 2010
    • If you get the “soft white” compact fluorescent bulbs, really, they are quite yellow. I’m changing over to them exclusively in rooms where I spend evening hours. Also trying the orange glasses. “Chromalux” bulbs also have a lot of red in them, and radiate heat, so they’re nice to use in a cool room in the winter.

      piano-doctor-lady wrote on March 5th, 2010
  29. I’m totally buying a fire pit. Thanks for the inspiration.

    Matt wrote on March 4th, 2010
  30. I’ve been an advocate of preserving sleep in order to enhance health, manage weight etc for years but hadn’t heard of the whole blue vs other light thing. Thanks Mark, very interesting.
    I have to say, I suffered insomnia severely for 3 years and one thing that did help (among other methods) was to force myself to cull the TV and computer a couple hours before bed. I think if people realised how much lack of sleep affects every element of their metabolism, health and wellbeing and not just their energy then they’d be far more motivated to do something about it.
    In my mind a sleep debt is one of the primary reasons for obesity and poor health.

    Kat Eden wrote on March 4th, 2010
  31. Great post — glad to see this topic getting more attention. Sleep deprivation and excess sugar seem to have near identical negative effects on the body and endocrine system.

    Thanks for the mention! I’ve just posted a detailed description of our “Month Without Artificial Light” experiment on my blog. There were both positive and negatives. The New York Times article I link to and quote from is a must-read for anyone interested in this topic.

    JD Moyer wrote on March 4th, 2010
  32. What is the difference between these blue light blocking yellow lensed glasses and yellow lensed night driving glasses? it seems to be easier to find the driving glasses, if they are essentially the same it seems much more frugal to go for the night drivers… any thoughts?

    Jess wrote on March 4th, 2010
    • They appear to be much more yellow than the orange cooper safety glasses. The orange cooper glasses block something like 90% of the blue light.

      I didn’t get much of an effect from some sunglasses that were fairly orange so I don’t think driving glasses will cut it.

      The safety glasses are only about $10. If your looking for something more comfortable or stylish you could give the cooper’s a shot first to see how it works for you.

      Mr S. wrote on March 5th, 2010
      • One thing strikes me, if they are night drivers surely it wouldn’t be safe if they were blocking light that might keep you awake, as being awake might be quite important when driving!

        Kelda wrote on March 5th, 2010
  33. I read a hypothesis of evolutionary a that small percentage of our ancestors were natural owls so they could guard others against predators during the nights.

    then i must be a descendent of them. haha (light therapy does not seem to work too well for me as my circadian clock is not very sensitive to light.)

    PHK wrote on March 5th, 2010
    • I’ve read that hypothesis too, Brain Rules? I hope it’s not true or I may be screwed. I’ve always had trouble falling asleep.

      The one thing that has helped me fall asleep is heavy exercise during the day. Though I usually end up ‘napping’ for 2-3 hours right after a long surf session and that makes me stay up later lol

      Thanks for the suggestions Mark!

      Dan wrote on March 5th, 2010
      • hi, Dan,

        are you insomniac or you’re just not tired?

        i am not insomniac. i can fall asleep in 5-10 min if i’m tired (which is between 1 & 2 AM)
        i am just not tired at all. so it feels very wasteful to me to toss in bed during my prime time when i feel most productive & alert. (i think it’s called “delayed sleep phase”. maybe you have it too.

        I just downloaded f.lux. i hope it works. like i said, light in the morning does not wake me up. i could sleep in a bright room in summer until noon. exercise also does not work for me.
        i have also learned that napping is a bad idea.

        at least my DSPS is not too extreme like others, so my constant “jet lag” is ONLY 2 hours for standard time (or 3 for DST).

        good luck.

        PHK wrote on March 5th, 2010
  34. My 6 year old is scared of the dark and insists on having quite a bright nightlight… should I be putting a red bulb in it? Will that help?

    PaleoMum wrote on March 5th, 2010
  35. Thank you so much for this article Mark. Definitely an Aha! moment for my fiance who has massive trouble falling asleep and coincidentally is on a laptop until late at night.

    Brett_nyc wrote on March 5th, 2010
  36. Has anyone tried to change out all of their light bulbs to non-blue light emitting ones? That was the first thing that came to my mind after reading this article..thanks Mark!

    Joshua B. wrote on March 5th, 2010
    • I just bought two yellow “bug” lights at Lowes. I check there and Wal-Mart but neither had one less than 60watt so the 60 is what I got. No amber night-lights either. I’m trying those bug lights out tonight to see if I should replace more of them. (I tried candles last night but the parents were over and we needed the lights and then later as I’m heading to bed the wife turned the lights on to get ready for bed which made me angry.)

      Jonathan wrote on March 5th, 2010
  37. I put F.lux on my computer, and now actually get sleepy during my late-night Stumble/blogging sessions. Wonders for my sleep schedule.

    Great post!

    NickW wrote on March 5th, 2010

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