Sleep, Sleep, Sleep! How artificial lighting and cortisol impact zzz’s

Hey there, been getting a lot of questions about the recent BBC piece on sleep. If you have not read that yet please do and then skeedadle back here.

So, the thrust of the piece is that “normal” human sleep (both from a research perspective and anthropological observations) is NOT a solid, 8 hour block. Research and anthropological observation indicates people should experience alternating periods of waking and sleeping. The article makes the point that many people experience “sleep anxiety” when they awake at night and then fret that they will not get back to sleep.

Ok. This article seems to have really spun people up and it’s produced not much more than a shrug for me. Why? Because instead of thinking about all this as an isolated concept I’m thinking about it from the larger evolutionary biology context (plus factoring in what I know about sleep research). Let’s revisit the opening section of that BBC piece:

In the early 1990s, psychiatrist Thomas Wehr conducted an experiment in which a group of people were plunged into darkness for 14 hours every day for a month.

It took some time for their sleep to regulate but by the fourth week the subjects had settled into a very distinct sleeping pattern. They slept first for four hours, then woke for one or two hours before falling into a second four-hour sleep.

 That “14 hours every day for a month” is my emphasis. Let’s think this through: If you live at the equator you generally experience about equal length of day and night (neglecting electricity for the moment). If you live at higher latitudes (either north or south) you will see greater variability in day/night lengths especially at very high latitudes in which folks may have 24 hour light (or dark) depending upon the time of year. Folks in these extreme areas tend to report a bit of…”squirrleyness” when the light/dark cycle is perturbed. Obviously folks adapt to and survive these extremes but it’s not comfortable relative to the periods when they have a more reasonable light dark period.  What the researchers did in the highlighted piece above is restore the OPPORTUNITY for something approximating our normal wake/sleep cycle. Folks were allowed 14 hours of darkness. Not far off what we’d see at equatorial levels most of the year…and they experienced “normal” broken sleep patterns. The key points here should be obvious but I think folks are missing them:
1-These people had 14 hours to potentially sleep.
2-How often does this happen in the modern world?
Our modern sleep patterns of a 8-ish hour blocks is an attempt to deal with a chronic stressor. We do not have as much time as is genetically wired into us for sleep, so our bodies do the best they can. When you look at the sleep of people who have stayed awake for many days you see this pattern played out but to an even more extreme degree. People who have experienced very long term sleep deprivation tend to bypass REM sleep and dive right into the deep level 3-4 sleep which tends to be the most restorative. We all tend to do much the same thing, just to a lesser degree.
That’s one piece of the puzzle, just the “sleepy time” segment, but we have another piece to this which relates to total photo period and peaks and troughs in luminosity. The ancestral environment  contained both more and less light exposure. We experienced more light from an intensity standpoint in that we got outside and had the sun on our skin (and in our eyes, establishing our circadian rhythmicity and setting the tone for the production of sleep hormones such as melatonin) and less in that once the sun went down we had starlight, moonlight or firelight. Indoor lighting by contrast is this kind of grey purgatory in that it is many orders of magnitude of intensity LESS than sunlight, yet many orders of magnitude of intensity GREATER than starlight. Indoor lighting is like chronic cardio relative to lifting weights and sprinting: not enough of an acute (hormetic) stimulus, too much of a chronic stress.
Check out this chart of relative luminosity:
It’s important to note that this is a logarithmic scale. The difference between direct sunlight>office light>starlight is not just “big” but “really big.” Why this is significant relates to a host of biochemical cascades tied to photoperiod, not the least of which is cortisol level. In this graphic we see a simplified cortisol level throughout a normal day:
Cortisol is relatively low at night (allowing us to sleep) higher in the day to stabilize energy levels and modulate immune function. Cortisol is highly responsive to photoperiod and “long days” as we experience them as artificial lighting tends to elevate cortisol. This can absolutely buggar sleep and crack open a host of problems with regards to body-fat levels, insulin resistance and systemic inflammation. This paper is but one of many linking sleep debt and a disruption to the neuroregulation of appetite.
Bottom Line?
The take away from this is that our normally hard-wired sleep patterns require a significant amount of rack-time to properly experience. I don’t know ANYONE (myself included) that is going to bed when the sun goes down. So, we experience a compressed sleeping window and sleep that does not look like our ancestral/phenotypic norm. The BBC piece is a bit disturbing in that they essentially make the point that if you wake during the night it’s “nothing” to worry about because that’s a normal aspect of normal sleep. Do you see where this is flawed? We don’t GET normal sleep, so we need to do the best we can to get the sleep we need under the parameters of our lives. The researchers and journalists should be educating people to get more sleep, more dark time. They are not. They are taking cues from our normal sleep environment and overlaying this pattern on our current pattern which is  a stress response to a compressed sleeping window and problems with photoperiod, both with regards to intensity of luminosity, and the problems associated with artificial lighting.

Categories: Anthropology, Paleo Diet Basics, Sleep, Weight Loss


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  1. Phil Bear says

    Awesome post, as always. We’ve got the darkness pretty dialed in at our homestead. Light absorbing curtains, door shut, etc. I have a question about alarms – we both have to wake up before sunrise, and I was looking into getting a natural sunrise style alarm clock.

    Thoughts on these? The BioBrite looked pretty solid, but if you have any experience, your feedback would be appreciated.


      • chris says

        Wanted to chime in. I recently got one of these because it was suggested at the biosig cert and the thing is amazing. It has a natural set and rise with light. So I can set a sleep time, like 30mins, and i can play natural sounds like water. the light slowly goes out, at the speed of sunset. 15 mins before I wake, the light slowly turns on and rises. WAY more peaceful then an alarm just immediately ripping me from my dreams. Reducing stress levels before sleep is also a huge part of this to get good sleep.

        • Deanna says

          When I was in college, I asked for a sunrise lamp, and my parents delivered with a very inexpensive model that starts to rise 30 minutes before the alarm goes off and sets for 20 minutes at night once you set the alarm. I have used it for probably 7 or more years now and feel absolutely lost without it — when I get a good night’s sleep, I start waking up naturally with the light. It’s absolutely wonderful.

          I also sleep with constant white noise in the background. Complete silence stresses me out somehow.

  2. Dan says

    Ah, but the bigger question is why do we not have time to sleep? What are we so busy doing, and what is SO important that we sacrifice quality sleep (and thereby health) to accomplish?

    I’m not saying it’s an easy pattern to break out of, but then neither is the habit of eating junk food (for many of us), but is the payout worth the effort?

    • says

      You’d be the VERY rare exception getting into bed at 8:15. Not that I’m discouraging that at all, but when people are trying to make sense of this stuff it’s important to be accurate in our time allotments.

  3. ben says

    nice explanation of the BBC’s piece. My anecdote is that I wake at least once per night, usually 2-3 times. At least one of those is accompanied by a quick pee. I always rise well-rested, etc. No probs. I have experienced the nervousness that I won’t be able to get back to sleep but I just think “sleep sleep sleep” seriously, and I fall asleep eventually.

  4. JC says

    So what’s the answer? Feel kind of squeezed here. Yep I agree it would be great to go to sleep at 8:15 and get up with the sun even if I woke in the middle of the night some time. Of course I’m not at all tired at 8:15 so that wouldn’t be easy and family, etc. won’t allow it. Reality for me is bed by 10-10:30 sleep until 2:30-3, awake for an hour fall asleep at around 3:30-4 and then get up at 6 or so. Not sure how to change that. Any advice for us with this kind of pattern? Some nights I sleep all the way through. Actually it seems I go through periods of the 2 patterns. I’ll sleep all the way through the night for a week or so and then go to the wake in the night pattern for a couple weeks then back. Not sure how to become more consistant.

    The room is pretty dark and I wear eye covers anyways. I have white noise playing all night to eliminate various noises that would wake me up. Not sure what else to do.

  5. Patti says

    We recently moved into an apartment with large floor-to-ceiling windows in the bedroom. Rather than fork out $500+ for blackout shades, my boyfriend found a comfortable sleep mask for me. Is that as good as a pitch-black room if light isn’t getting through the mask?

    Phil, The Progressive Alarm Clock iPod app wakes you gently with the sound of a Tibetan singing bowl.

  6. marie curious says

    Robb, terrific ‘catch’ of the problem with compressed sleep allotment and thank you also on a personal level, you just explained why, when not socializing, I gravitate towards going to bed at 9pm (eyes very droopy), wake up at 3am with the desire to do scholarly work/reaearch (!) or to just read then sleep again around 5am until 8am. I finally stopped fighting this just last year and adjusted my work schedule to accommodate, but felt guilty of being ‘indulgent’ all this time. Now I feel better!

  7. George Goodall says

    I spent a year living in rural Nicaragua. Going without power for days was a common experience. Quando no hay luz, everyone would just go to bed after dusk and we all fell into a similar sleeping pattern: sleep, wake, sleep, get up with the sun. There were times when it felt like everybody got up for a party in the middle of the night! When there was power everyone would just stay up watching TV and feel crappy the next day. For some reason, a dubbed version of X-Files was very popular: “Cuidado Mulder!”

    Unfortunately, I wasn’t in the Corn Islands. I did, however, spend some time on Little Corn where I experienced just how much damage 130,000+ lux could do to my gringo back!

  8. says

    I recently did an experiment where I did 4 days/5 nights without artificial light (and most other modern conveniences.) I put away my clocks so I didn’t know the time except what I gathered from the placement of the sun. It was completely dark outside from 6pm to 7am except for streetlight and I limited that as much as possible.

    I found that the first night I slept almost the entire night – I’m guessing about ten hours. After that, I found what the BBC reported. That I slept solidly for a few hours then wake/sleep until it got light. Besides, there is nothing much to do when it gets dark except read or write for a bit then sleep.

    With our ability to get artificial light we have effectively extended our day, shortened our sleep time *and* filled those extra waking hours with a form of activity. It is no wonder we are chronically stressed through lack of rest.

    And having said that, I am here at 10pm on my computer, lights on all around me. I need to pay attention to my own conclusions.

  9. says

    This article is really interesting. I just started a website about monthly challenges, I have already decided to work on my sleep pattern in March or April, but this info changes everything.

    I was aiming for being in bed before 11pm. Maybe I should go to bed 9o’clock, wake up around 1-2am and get my 4 hours from 3-4am? Or should I just stick to my regular 8 hours from 11pm challenge?


  10. Kenny k says

    Good stuff Rob! I work a night shift starting at 10pm and ending 6am. Im really trying to eat well and be a workout warrior. Is there anything I can do to feel normal on a regular basis? any tips? Everyone I work with seems content with feeling like crap and there is zero education about dealing with nights from our department. I know its off topic but would love to hear if you can help!

    • dave says

      Here is what I did but in the end it still felt like a fog was lifted when I left the grave shift and my memory of it was a bit of a blur…
      1. strict sleep schedule. I scheduled sleep once I get home till afternoon and kept that schedule even on weekends. schedule any time you want but consistency is key.
      2. there is no day and night there is only awake time and sleep time. meals happen while waking time. So you disturb your sleep as little as possible.
      3. Sleep in a comfortable very dark place I pulled sleeping stuff into my walk in closet for additional light and sound insulation as it was centrally located in my home. weird but it helped.
      4. Make sure to get some sun once you wake.
      5. Pack enough lunch too. having a decent estimate on how much food will get you how long can be helpful so you aren’t constantly gorging yourself before bed time.

      Plan an exit strategy unless you are really comfortable with that schedule or the only way you can make money. Like I said, it is like you are in a fog the whole time, sometimes you don’t notice it while you are in it. If you vacation, try a different time zone so you can take advantage of your already shifted sleep/wake schedule.
      good luck.

  11. says

    I thaught I had some sort of sleep problem. Wake up after 3 or 4 hours, take a leek, then lay in bed for an hour or 2 before falling back into a fitfull sleep. Now I think I may need to experement with this get up and do stuff thing. At 65 years old I thaught I was getting too old to sleep well. Life can be complicated. Lot of variables. Stress, light levels, diet, monkey mind. Now I will lay awake thinking about this stuff.


  12. says

    Totally agree with Dan’s comment already posted: what is it that keeps us from getting to sleep at a reasonable time? Yes, for those with shift work, or small children/babies who don’t sleep, or other logistical factors that prevent a circadian approach to sleep, this might not be feasible and require lots of workarounds, but I’d venture to guess that there are at least as many people who could do without the TV or online time after supper that don’t know yet to make sleep a priority over those things. (I count myself among those who are working to achieve less screen time and more shut-eye time :-))

    I also found the relative luminosity chart helpful. The more we know about the light sources and exposure we do get, the more we can “tweak” it to something closer to what we’ve evolved to get naturally.

    Thanks for this article. Knowledge is definitely power!

  13. OogieM says

    um, some of us do tend to run by sun cycles. We generally go to bed when we are tired, usually soon after full dark, and get up with the sun because the bedroom window faces east. Of course, working at home makes this possible and since we farm, the animals already work on sun cycles so it’s a good fit for our work.

  14. Trevor says

    Good article Rob as always. And it comes at my first week working the graveyard shift. I’m thinking I need to get off nights as soon as possible. It’s going to be about a month but I’m already looking forward to getting off nights.

  15. says

    The point of the BBC article for me was that I don’t need to stress as much (thus making it hard to go back to sleep) when I do wake up in the middle of the night. I would often wake up and lay there worrying about it and that would make it all the worse. Although I have found that since I drink so much less living the Paleo lifestyle that this happens much less often.

    I have also found that some days I am so tired from living life that sometimes I do fall asleep on the couch at 8pm. Then when I get up to go to bed I have a hard time getting back to sleep. I have found that if I don’t stress about it and read or something for a while that I can get back to sleep and not be stressed.

    For me I think the answer is to get to bed at a reasonable time and if I sleep all night great but if I wake up in the middle of the night not to stress about it.

    • Philip says

      I agree with this. I had always been a poor sleeper. Then a couple years ago I learned about sleep cycles, and along the way observed that sometimes my wife or kids would say that they were up all night–even though I knew they weren’t. It gradually dawned on me that part of the cyclical nature of sleep includes phases of consciousness along with phases of unconsciousness (i know that is a poor choice of words). Eventually I got to the point where, in trying to get my 8 hours, if I “woke up” I would just tell myself “this still counts” (ie toward the 8, because it just represents another stage of sleep). From that day, I have had virtually no trouble sleeping.

  16. Umm Musa says

    Dear Robb,
    Thank you very much for taking the time to review this article. When I read it a day or two ago on BBC, I thought ‘if only Robb would see this and comment’. And, as so very often, you DID!

    I agree with your comments and most of the responses above. We have blackened out our bedroom, keep lights in the house on minimums with dimmers and try to go to bed between 20:00-21:00 most nights. When I am rested and mindful to avoid strong lights (and TV, though a bit of Paleo reading on a dimmed iPad works fine), I tend to wake up for a little while in the middle. However, after a long hard day and when going to bed later, my sleep pattern is more like a solid block with about two semi-conscious states in-between. I prefer early nights and mornings anytime.

    • Axel says


      Thanks Robb for the great article, and thank you Umm Musa for sharing your experiences. I’m highly motivated to try this sleep pattern. After I’ve taken care to black out my sleeping room at night and recently bought a sunrise light/alarm clock (works great!) I am improving, but I still feel that there is room for more improvement.

      The big catch for me is, like surely for all of you as well, that I feel I can’t afford to “lose” so many hours of the day to bedtime or (dark hours). So when contemplating about a real life experiment my first question was ‘how could I make use of the time between the two sleep phases?’

      I guess reading is a very nice use of this time. What are your experiences with the digital reading? I read that light emitting devices (like your iPad) trigger the same hormon response in our body as room light. An ebook reader like Amazon’s Kindle that does not emit light by itself might be diffcult to read under starlight (or some heavily dimmed artificial lighting).

      I could probably switch to audio books…. :-/

      Suggestions anyone?

      Thanks again,

  17. Pedro says

    Good post amigo!

    The BBC piece reminds me to be cautious: emulating our HG ancestors lifestyle is not just adopting one or more isolated (taken out of context) variables, it is adopting a “package”.

    Diet and exercise, without taking care of chronic stress, sleep and sun exposure will not lead to optimal health. And there’s also pollution, the hygiene hypothesis, breastfeeding, etc, etc.

    I have discovered the importance of stress, sun and sleep the hard way. These days my goal is to get at least 30 minutes of sun exposure/daylight and sleep 8-9 hours EVERY NIGHT in a complete dark room.

  18. says

    From what I took from the BBC article when it was posted a few days ago was that the four-hour broken sleep was a product of a pre-industrial revolution lifestyle. Even if it would be fantastic to have the quiet although physically back-breaking life of a peasant from 4 or 5 hundred years ago, that is not our reality. All the article was suggesting was that there may be a scientific and/or cultural explanation for why many people wake up in the middle of the night and that it’s no reason to stress yourself out more if you can’t immediately fall back asleep.

    In my personal experience I start to get sleepy when it’s dark and I wake up when my room is light. There are the odd exceptions like getting ready for work in the winter, but I find when left to my own devices, this is what happens. Sometimes I find that people stress too much about not stressing too much.

  19. says

    This is great Robb! I also find the best way for me to have a normal sleep, lights off is one. Besides, after a good night’s sleep I would be productive, mentally sharp, emotionally balanced, and full of energy all day long. Who wouldn’t want that?

  20. says

    Thanks for putting all this together Robb – I’ve read your book and the part on sleep has changed my life. Now, if I could get my kids to go sleep a little earlier I’d be all set!

  21. says

    Great article Robb, I didn’t see the BBC piece until you brought it to my attention. I hope that everyone that reads this piece has the chance to read your response to it.

    On a side note, why didn’t you participate in Paleo Summit? (

  22. Ruth says

    Great Post. I was reading just recently that an Australian study found that we (Australians anyhow) are getting enough sleep, which surprised me a bit, but perhaps we’re pretty contented given that we’re not suffering mcuh post-GFC. Sadly, I can’t remember where I read this info. Like the 65 year old correspondent above, I also sleep in batches of 3-4 hours. I had 3 hypotheses about why this might be so: getting older; perhaps having some residual problems with high normal BP; and switching to a paleo diet, which makes me want to pee at night more often. But the good news now is that it’s one less thing for me to worry about.

  23. says

    Hi Robb!

    Great post – I’d be interested in a study showing how technology and computer use has affected our sleep. No doubt it has. I use an app called F.lux which imitates sunlight as the day passes on, as to not emit cold, blue light.

    This post has inspired me to get off the computer at a certain hour way before bedtime. Now, if I could just *stick* to it!

  24. says


    All due respect. I loved your book.

    The main point of the article was not that one shouldn’t worry if we awake during the night, but that it is natural. If people understand the nature of their wakefulness at night they will be less inclined to be anxious about it.

    You are considering that we don’t get “normal” sleep, because we don’t have “normal” lighting, but alot of people do. Consider people who don’t use a televison or computer when the sun is down. I am one of those people. I turn on a lamp that I feel mimics the intensity and color or firelight and I will read or talk with my family. I go to sleep about four to five hours after the sun goes down and I often wake up at about 3 or 4 in the morning to find that I’m awake and alert. I can go back to sleep but I don’t find the sleep restful until about 5 AM.

    So, as anecdotal as it is, if I don’t find that my sleep is restful from 3 – 5 am I getting much benfit from it?

    What kind of detriment do you think the eight hour sleep is having to our health?

    You seem not to be too concerned with this, but you might want to re-think “shrugging your shoulders” because according to your book you never knew how “normal” a “normal” Paleo diet could make you feel until you tried it. You could be missing out on a new “normal” and you would never know.

    You can make the argument that it’s impractical, and I could make the argument that Paleo is impractial.

    I know it would be hard to draw any conclusions on the benefits of “normal” sleep vs. the eight hour sleep, because there are probably no studies done on that subject, but shouldn’t you be leading the charge on this?

    I knew a type-I diabetic (all his life) that drank heavily and lived to be in to his eighties who slept the “normal” way. I often wondered how he lived so long, and this makes me wonder now.

    Matthew Caton

  25. says

    Great Post,

    Really loved it,

    We need some time to find our perfect sleeping conditions but we cannot already avoid completely from dealing with the situation.

    As you said, we cannot go to sleep with the sunset, we are part of the modern society, but a solution has to be found :)


  26. terrence says

    I have a really neat device called a “Zeo”.

    You put on a very comfortable head band that has three sensors. In the morning you, the recording unit will show a time-line graph of your sleep. You plug an SD card into your computer, go to the web site, and upload your night’s data.

    You can see detailed graphs of your nightly and weekly sleep.

    Zeo records Light Sleep, REM Sleep and Deep Sleep, as well as how often you woke up, and for how long. I get pretty good sleep, but I usually wake up during REM sleep – which means it takes a long time to get out of bed, I am groggy and tired for much of the day. We should wake up during Light Sleep – which I am working on. I am trying to figure out how to have the Zeo alarm wake me in Light Sleep (apparently you can).

    You can buy a Zeo OTC in Canada; but, I think you need a prescription in the USA. If you have sleep issues – GET ONE, ASAP! You will learn a LOT about your own sleep, and how to fix it.

    One note – when I wake up at night, I am usually NOT wide awake (if I do not move around much (I do NOT get out of bed, or I will wake up)). However, the Zeo cannot always distinguish between my REM Sleep and my barely waking up. This is not a problem, but I do have to “interpret” the graph.

  27. says

    This is great. I have been having trouble falling asleep for the past couple of weeks and this sheds some important light on the “whys”. I found another commentor’s post to be of interest- technology and the effect on our quality of sleep. I don’t know if there is much data out there to support a whole post, but it would be an interesting read if there was…

  28. Brian says

    I have been looking for kid night lights that would trick the kids into sleeping with no lights. Something like a touch light with a 30-ish minute timer. Something they could turn on to keep from getting scared, if they woke up, but would automatically shut off and leave them in the dark after they fall asleep.

    There are some with 5 minute timers, but I am not sure that will get the job done. Any body had this problem or have a solution?

  29. David says

    Question: How about this scenario?, with the following conditions

    1. Dark Sleep Mask (covers eyes)
    2. Dark blanket that covers most of the body (most of the skin, or from neck to toe.)
    3. Dark sleeping clothes (optional, since the blanket is supposed to prevent light getting to my skin)
    4. Not so dark room (hard to do unless I find a box to sleep in.)

    The problem is I have a wife and a baby that sleeps in the same room, and the wife does not like to be in total darkness just in case the baby wakes up in the middle of the night.

    Although she has agreed I can get a box to sleep in for total darkness as long as it does not look like a coffin. I’ve seen a design that doubles as a table during the day.

  30. tycoon7 says

    Very interesting topic. But there is no proof that the ‘right’ sleep pattern is better for you. There lots of studies that night owls(wrong sleep pattern) have advantages. Here is the quote:

    “Night owls have been shown to be cleverer than larks, with quicker minds and better memories. They also earn more.”

    Your thoughts?

  31. Becky says

    Hi Rob,
    I’m a new Robb Wolf cult member (I also belong to the Fat Head cult)! I’m convinced that my cortisol release is reversed. I’m exhausted in the morning and for most of the day. When I get home I’m pretty tired until right before I have to go to sleep. Then I’m WIDE AWAKE. As I’m trying to sleep my heart starts racing. I’ve been taking Benadryl for years now to induce sleep, which I’m sure is awful. Have you addressed this topic? How can I reverse this issue? I’ve also tried pre-bedtime exercise, sleepy time tea, etc. Help!
    Thanks for providing so much info!

  32. says

    I found you through the Fat Head site; I started sleeping poorly when peri-menopause started and at one point didn’t really sleep for 6 years. A little better now but most nights are bad; I want to get “into” the phase sleep as I usually, when I DO fall asleep, wake up 2-3 and can’t get back to sleep at all, having to get up at 6am for work.

  33. says

    Wow. Robb, the research you put into your articles is truly amazing. I’ve suffered from insomnia my whole life, and for the past year have really made an effort to darken my bedroom and give myself more time to sleep. I’d heard that people tend to have this kind of bifurcated sleep before, but never put the pieces together.

    I’m one of the few people who actually has the luxury of giving myself more than 8 hours to sleep, if I really want to. Do you think I would need 14 hours of darkness a day to adjust to a schedule like this, or would ten hours of darkness do the trick?

    • says

      I honestly do not know, I’d ping that question to Doc parsley. I suspect the time necessary will also vary on latitude and time of year. Seattle in winter is likely easier to see the bifurcation than seattle in the summer, due to the photoperiod, but I’m guessing on that!

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