How to Conduct a Personal Experiment: Yellow Light Exposure (plus an Announcement)

You guys ready for another personal experiment? I hope so. Even if don’t think you’re ready to take something on, I’m confident you’ll be able to handle this one, because it’s relatively simple, intuitive, and easy. It’s also something I’ve been discussing for a couple years now, so you’re most likely familiar and comfortable with the concept. But most importantly, today’s experiment is a gentle one that requires very little commitment. No jumping in freezing cold water, no drastic changes to your sleeping schedule. All I’m asking you to do is experiment with nighttime yellow light exposure.


Remember how I wrote about nighttime exposure to blue light affecting melatonin secretion and, subsequently, sleep quality and duration way back when? Yeah, that. In case you didn’t read it, I’ll give a quick explanation:

The color (or wavelength) of the light we perceive entrains, or “sets,” our biological clocks, also known as circadian rhythms. And in the natural environment, with its reliably consistent lighting schedule, it works pretty well. During the day, we see all the visible wavelengths provided by the sun, including violet, blue, green, yellow, orange, and red light, and this “tells” our bodies that it’s daytime, that’s it’s time to be active, to hunt, to gather, to build, to work, to exercise, to study, and so on. Secretion of melatonin, the “sleepy hormone,” is blunted. At night, when the only visible light is historically the longer wavelengths, the yellows, oranges, and reds which we create through campfires, or candles, or gas lamps, melatonin secretion is unaffected. We get sleepy like we should, when we should. All is well. And if we had evolved to be nocturnal, like rats, all that low-wavelength blue light exposure available during the day would let us know it’s time to sleep.

But we don’t use candles and oil lamps at night anymore, do we? We use white LED lights (blue light) and stare into laptop (blue light) and high-def TV (blue light) screens. We use our iPhones (blue light) or Androids (blue light) in bed, even waking up in the middle of the night just to check our email (blue light) because “why not, we’re up anyway!” To really get a sense of this, next time you take a nighttime stroll around your neighborhood, pay attention to the living rooms of the houses you walk past. If they’re got their plasma or LCD going, the lights off, and it’s dark out, the entire room will be bathed in an overpowering blue light. It’ll look like a scene from an alien abduction movie or something. Of course, whether the room lights are on or off, that blue light from the screen is still there, beaming directly into the eyes of those present and affecting the secretion of their melatonin.

And we wonder why we have so much trouble getting good sleep.

It’s not just sleep that’s affected (although that’s enough reason to take heed). Disturbing our circadian rhythms with improper light exposure may have a range of other health effects, including, but not limited to:

When I say “yellow light exposure,” what I’m really talking about is “blue light avoidance.” Today, I’m going to show you how to put together an experiment to test the effects of exposing yourself to yellow/orange/red light and avoiding blue light. Although that sounds like we’re testing two things, we’re really not, since yellow light has little to no effect on our melatonin production. For all intents and purposes, it and other, higher wavelength lights are neutral, while blue light is antagonistic to our circadian rhythms.

Okay, so how do I do it?

First, choose a goal that yellow light exposure and blue light avoidance might help make possible. Since we can’t really test our susceptibility to cancer in a short trial, nor does metabolic syndrome develop in mere weeks, let’s test the effect of yellow light exposure (and blue light avoidance) on some aspect of our sleep.

  • “I want to feel more refreshed in the morning.”
  • “I want to go to bed by 10 PM every night.”
  • “I want to have more melatonin in my morning urine” would be an effective way to test, but it also requires being able to test your urine for melatonin. Most people don’t have that on hand. Let’s go with the second one – getting sleepy and in bed by 10 every night – since that’s easy to quantify (did you go to bed at 10?). If you already go to bed at 10 PM, choose a time that’s earlier than your normal bedtime. The key is to find out if you get sleepy earlier without the blue light.

Come up with a hypothesis, such as:

  • “Since blue light exposure suppresses normal melatonin secretion, and melatonin makes us sleepy, exposing myself to yellow light and avoiding blue light after dark will help me get sleepy and go to bed by 10 PM.”

Next, identify some of the variables that could affect the results of your experiment:

  • Activity at night – Does what you do while avoiding blue light affect your sleepiness? Is reading more stimulating than hanging out with your spouse?
  • Electronics usage – Assuming you’ve taken steps to eliminate blue light exposure (wearing blue light-blocking goggles, installing f.lux on your computers), do electronics still stimulate you and keep you awake?
  • Yellow light source – Does a yellow light bulb act differently on you than candlelight?

Then, let’s take some measurements. What should you be measuring?

  • Bedtime – When did you get into bed?
  • Sleepytime – When did you start getting noticeably sleepy? Time of first yawn?
  • Sleeptime – When did you fall asleep? This is hard to measure without equipment, but you can probably approximate it. Personally, once I get too tired to read another page and find myself nodding off in the middle of a sentence, that’s my sleeptime, because I fall asleep as soon as I put the book down and turn off the (yellow) light.
  • Morning wakefulness – On a scale of 1-10, how awake and refreshed do you feel in the morning?

After a few weeks you should have enough data to start making some observations about what does and doesn’t work for you, and from there you can decide on what to test next, if anything. That’s it for this experiment. Have fun!

Thus concludes this short but sweet series on self-experimentation. What’d you think? I for one am a firm believer in the power of the self-experiment. In fact, I think it’s the ultimate arbiter of an individual’s ideal path to health. Sure, you could read all the blog posts and studies and papers and research in the world, but if you personally experienced results that completely contradicted the advice of the experts, what would you do? Would you continue down the path that supposedly worked for this cohort or that quadrant of some population somewhere? Or would you stick with what worked for you?

Exactly; we are complex beings with physiological processes that even the experts who study them for their entire lives don’t fully understand. Everyone is different, and there are no real one-size-fits-all plans – not any honest ones, at least – and so self-experimentation (even if it’s just an informal thing) is absolutely crucial and highly effective.

In case you missed the newsletter announcement this week: next Wednesday, my new book, The Primal Blueprint 90-Day Journal, is being released! As usual, there will be a very special early-bird offer. I’ll be throwing in some limited-time freebies, and doing a big day-of announcement, so check back here on June 27 and be ready to take advantage of the offer.

Now let’s hear from you. If you have any questions or comments about this self-experimentation series, leave them in the comment section and if there are enough questions, I’ll do a Dear Mark on self-experimentation next week. Thanks for reading!

About the Author

Mark Sisson is the founder of Mark’s Daily Apple, godfather to the Primal food and lifestyle movement, and the New York Times bestselling author of The Keto Reset Diet. His latest book is Keto for Life, where he discusses how he combines the keto diet with a Primal lifestyle for optimal health and longevity. Mark is the author of numerous other books as well, including The Primal Blueprint, which was credited with turbocharging the growth of the primal/paleo movement back in 2009. After spending three decades researching and educating folks on why food is the key component to achieving and maintaining optimal wellness, Mark launched Primal Kitchen, a real-food company that creates Primal/paleo, keto, and Whole30-friendly kitchen staples.

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110 thoughts on “How to Conduct a Personal Experiment: Yellow Light Exposure (plus an Announcement)”

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  1. I love the glasses from I’ve been sleeping a lot better since using them.

    1. The science behind lowbluelights (and what Mark is writing about here) is completely legit. Blue light exposure at night, and the corresponding melatonin deficiency that it produces is responsible for a whole host of health risks, the most noticeable being insomnia. However, as can be seen in studies of shift workers, melatonin deficiency is also linked to sinificantly increased risks of diabetes, obesity, and cancer (a meta-analysis of 13 independent studies found that melatonin-deprived shift workers had 48% higher risk of breast cancer).

      The options for low-blue lighting were so few (and expensive) that I started my own company, producing more reasonably-priced blue blocking glasses and amber book lights:

      The amber book light in particular has done wonders for many, many people’s sleep disorders.

      I’ve also compiled all the latest research on light and melatonin at the above site (much of it stuck behind academic paywalls, sadly), if you’re interested in checking it out!

  2. I’m excited to try this around my house. When my husband was a child, his mom kept the tv on all night, so now he needs it on to go to sleep. When I turn it off at night, he’ll often get up and go sleep on the couch just to have the blue glowing light. It drives me insane because he is always complaining about how poorly he slept and how much coffee he needs to get going every day. I’ll try switching to yellow bulbs in our lamps first and getting him a few books to read. Then maybe I can move towards candlelight, which I absolutely love to use when reading! I’d really like to try this with our kids, 5 and 6, and will try to find small yellow nightlight bulbs since they are terrified of absolute darkness. Does anyone have good nightlight suggestions for wee ones?

    1. I certainly want to try this (and pardon my ignorance) but where do I get a “yellow” light bulb? I didn’t realize the bulbs in my lamps came in different colors other that what you buy at the store….I have tried to read by candle light but it just isn’t light enough for me to actually read without straining…Would love to know more about “yellow” light bulbs…Thanks

      1. Look for “warm white” bulbs, not “daylight” (the coolest) or “cool white.” That should get you the warmest color temperature readily available. Keeping the wattage low (20-40W in a bedroom is plenty for reading if the light is nearby) helps too I think.

      2. I think yellow light bulbs are just regular light bulbs (called soft white??). The LED or halogen (long-lasting) are blue.

        1. Philips LEDs that work in standard incandescent fixtures give off a warm toned light. The lights are yellow when not turned on. They also only use 12.5 watts (for 60w equivalent) and last more than 20 years. They don’t produces much heat, turn on almost instantly and have no mercury as well.

        2. actually a reply to Bob below, but didn’t get a reply link. Phillips and other LED lights may show a yellow bit underneath when off, this doesn’t mean they give off yellow light. Rather this is a bit of phosphorus that converts the blue light of the LED into white. These are NOT a source of yellow light, and do contain the blue wavelengths. Do not use these at night unless you filter them.

      3. Incandescents will throw off yellow light. Think about it, its just a burning filament – fire! Likely one of the reasons that we were so easily able to transition from candlelight to electric lighting.

        1. They’re now making LEDs in different colors like warm white, which is great since they use so much less energy than incandescents. And incandescents have warm white and cool white, so whichever one you choose, go for the warmest color.

        2. In Australia yellow bulbs (incandescent) have been outlawed. We are permitted to use led’s, halogen (my choice in small 40 (bedtime) or big 100 watt (evening) bulbs) or fluro’s (BAD BAD IDEA!) which give everyone headaches. ‘Law’ should be coming to the States soon.
          Paul Wheaton at permies does a fascinating and simple experiment on how truly evil this is. He rants coherently about how dangerous, ugly, unnatural etc. these are, particularly if they break.
          Save the planet with fluro’s, ha ha ha. Not.

      4. Home depot sells the new curly light bulbs in many colors. I bought an orange one for my bedside lamp. I know it works because anything blue looks black in that light.

        1. These are exactly what I use in the bedroom lamps. They make me feel sleepy very quickly – in less than half an hour of using them.

      5. Most LEDs and compact fluorescent bulbs have a color temperature rating these days. You should be able to find it on the packaging. The spectrum ranges from 2700 to 6500, measured in Kelvins. The lower the Kelvin, the redder the light, and vice-versa, so, for example, a candle is approximately 1800 Kelvin, and summer sunlight is 47-57K.

    2. I bought simple basic nightlights along with 5W red lightbulbs in the Christmas clearance section for my kids. I also got them different CD/Radio alarm clocks with red lights in them. They had green. It doesn’t really matter for my daughter but my son sleeps much better because he wakes up at night and looks at the clock.

  3. I’m still too busy looking for camel meat to try this …. ; )

  4. I’ve been wearing blue light blocking glasses at night for a couple of months. They make a big difference. Combined with a cold bath for 30min before bed and I fall asleep nearly immediately (used to take at least 15-20 minutes).

  5. Check out Amazon for Uvex S1933X Skyper Safety Eyewear (lowbluelights has similar glasses, but priced at 8x as much!)… these safety glasses allow you to use your “blue light” devices at night, and not mess up your circadian rhythm. I put these “stylish” glasses on after sunset, and I’m drowsy by 10pm and out like a light!

    1. You really only need orange tinted glasses, right? Thanks so much for posting a cheap option that worked for you! I’m just not willing to shell out 50 bucks for orange glasses.

    2. Thanks for the recommendation… Gonna check these out for sure!

  6. The questions that come up for me here have to do with seasonal light in the Northern climes. We are above 48° longitude and at this time of year we have about five hours of darkness. We find ourselves not able to even get inside until 9pm, and getting the kids tucked in before 10pm is a trick, so us parentals getting to bed before 11 just doesn’t happen.

    The kids stir and whine at first light, around 4am, then go back to sleep for a few hours, but on rainy days even we grown ups switch off our alarms we have a sleep-in.

    In the winter, when things switch and we only have five hours of daylight, we can have the whole family in bed by 9:30 and sleep until we’re done sleeping.

    Should we be concerned with the lack if sleep we get in the summer? It seems completely natural to us (if a bit disconcerting to other parents) to follow this seasonal “sleep when it’s dark” habit. The sun and blue sky are rare commodities here, so giving them the pass for some sleepy time is a tall order to fill.

    1. We use dark curtains and blinds. I bring the kids inside by 7:30-8 if possible (mine are still elementary school age), and minimize light exposure. Bedtime is 9 at the latest. They usually fall asleep pretty quickly!

    2. I wouldnt worry. We are 59* longitude, that is – no darkness at all. The sun is just below the horizon for 4 hrs but it’s never dark.
      I sleep a lot less during the summer, it feels like a waste of time not staying up enjoying the light…
      Because in just 6 months I will live in almost constant darkness, and can and will sleep more.
      So it’s like a seasonal biphasic sleeping cycle, feels quite natural to me.
      Mark, funny you started this experiment just at the longest days of the year… At midsummer time in Sweden, when we swedes tend to stay up all night having The Party of the year 🙂

      1. I’m only at 53 longitude, but this still means sunrise at 4:30, sunset after 10 pm. Despite blackout shades and such, I find my kids just won’t go to bed at their “usual” time during the summer, no matter how religiously we follow a normal routine. I’ve heard that we need less sleep in the summer when it’s light for much longer, and although I don’t FEEL like I need any less sleep myself, it seems like my kids are a perfect example. They are no worse for the wear despite getting an hour less sleep. So I guess if my sleep were more in tune with my natural rhythm (as opposed to being dictated by work, chores and TV), I might notice this difference, too.

  7. For computer users F.lux is a free program that automatically adjusts the light your monitor emits based on the time of day. So as night approaches the light from your monitor will gradually change to a nice orange glow. All you have to do is turn off your house lights and get sleepy.

    1. I’ve been using F.lux for well over a year now ever since Mark recommended it and it definitely works! I no doubt feel sleepy around my usual bedtime even when I am on my computer now.

      However, I much prefer NOT being on my computer near my normal bedtime.

      1. I use F.lux, have it installed on both my laptop and computer but I don’t keep my monitor on all night so it doesn’t matter. But if I do have to be up late and use my computer it really helps my eyes and does not make it hurt after I turn everything off.

      2. Me too,
        I don’t want to jailbreak my iPad, so I am simply not going to use it in the evenings. I have nearly adult sons, who do a lot of “devicing”, though not as much as some (!), so I am going to start to include non tv nights, using cards and board games. We so very rarely do this but really enjoy it when we do!
        I luv candles, and since electricity has gone up in cost by 70% over the last few years (I kid u not), they are much more compelling.

  8. Thankfully, my alarm clock has a red light display. My husband wanted a blue light display but I complained that I felt like I was sleeping with the sun on. I love candles and firelight. They are so relaxing. If someone feels like candle light is too dim to read by try getting a hurricane lamp that uses oil. You can vary the intensity of the light and it is yellow light. Plus, you don’t have to worry as much about an open flame. You could go really old school and use wall sconces that are for candles and have a mirror to throw the light. I love alternative lighting sources.

    If you still have some crisco from before going primal you can use it for its original purpose, as a candle. Good cheap lighting source. You could even make your own candles with the crisco.

  9. I ran this experiment a while back. I had onset insomnia for years – often took me 1-2 hours to fall asleep.

    I had flux on my computer, and I tried not using it after sunset. I tried a few other things such as no coffee, cold showers, exercise before bed.

    Nothing worked.

    Then, I tried one final experiment. I didn’t have flux on my iphone. But they released a Cydia version, so I jailbroke my phone and installed it.

    Instant disappearance of onset insomnia. It was shocking. I can use my computer as late as I want, with the blue light gone, I seem to be able to fall asleep quickly.

    I wasn’t using my phone much at night, but it’s also my alarm clock, so I had to look at it each night.

    If you have a phone, install flux on it. It’s worth a jailbreak.

    Note: I have no TV, and all my lightbulbs are incandescent.

    1. How legit is jailbreak? I’ve never heard of the term until now. I did some research but I am skeptical. I refuse to let anything happen to my iPhone as I just got it 1 month ago.

      I would love f.lux as I currently read on my iPhone – blogs and I use the kindle app.

      I’m just worried of course. I have a white iPhone 4. What is the safest way to go about doing this?

      If I do it…

  10. I actually started doing this about 2 months ago to treat adrenal fatigue. I’ve only skipped a couple nights but here’s what I do: zero electronic use aft the sun goes down. I try to get a shower while there is still natural light outside. If not, I shower by candle light. I prep for bed and take my candles to my bedside. I’ve used black out curtains and will not use electricity. Right now my bed time ends up being between 8 and 9. I read by candle light for about an hour and end up getting sleepy around 10 or 11. Results: I used to wake up at 9 or 10 am and could have slept longer. I now feel awake around 5 ish, but I don’t get up til the sun does which is around 7 ish. I am a night owl for sure, but now I’m becoming more solar powered.

  11. Go to bed by 10 p.m.? I usually turn the reading light out by 8:30 p.m. I get up at 5 a.m. I usually fall asleep quickly, but after 2-1/2 to 3 hours, I wake up an have to use the bathroom. I usually fall asleep fairly quickly after that, but sometimes not. I wake up–bathroom call or not–at least three or four times during the night. I only use my computer during the day and almost never watch TV at night, and I don’t own a smart phone. (I’m an old guy, 65, and can get by without being electronically connected to everybody I know, or the rest of the world, at all times.) Some nights I will wake up at midnight or one and be wide awake and won’t go back to sleep for two hours. And this could be genetic. Both my sister and brother–sister 3 years younger, brother 3 years older–are the same way. My sister’s husband, however, watches TV until his bedtime, ususally around 10 p.m., or is on his computer or smart phone or i-pad (yes, he’s one of those) and, according to my sister, when his head hits the pillow he’s asleep and rarely wakes up during the night. I know that I’ve always been a light sleeper, even as a teen-ager, lo so many years ago.

  12. There’s no f.lux on Android. What do you all think of CF.lumen (which my HTC Incredible suggests when I ask for f.lux)

    1. I’m wondering about an app for the iPhone. I am just not sure on jailbreaking as someone mentioned above.

      Does anyone know of an iPhone app that is similar to F.lux on your computer?

    2. I saw that one, but similar to F.lus on i-phone, I think it requires rooting your android. But there’s a program called “Lux” on Android, which will allow you to have various modes of automatic backlight adjustment to match the brightness of your environment (including dynamically). As well as a night viewing mode which cuts the blue light. It doesn’t kick in on auto with sundown, unlike F.lux on a computer, though…I think it’s very good, but it drains my battery..The writer gives an unconditional money-back guarantee though if you want it.

      1. Yes Lux on Android does the job, you can save battery by having it manual adjust rather than auto.

        My partner and I have been following this kind of regime for about a year, combined with getting outside for bright daylight for at least 20 mins each morning. It makes a big difference to sleep quality. All our lights in the house are old incandescent bulbs of low wattage which really helps, and we have strings of red and orange christmas fairly lights (incandescent of course) to light areas such as the kitchen which we go into only occasionally through the evening. All lights off before starting to prepare for going to bed.

        However this is not the time of year to try this in Scotland, there is enough blue light from the sky to read by at midnight! And our house has big windows and north-facing skylights!

        1. How do we cope with the light? Go to bed late, wake up early, I guess, and look forward to the winter (dark before 4pm, sunrise not till nearly 9am).

  13. “I for one am a firm believer in the power of the self-experiment.”

    Me, too. I firmly believe that the relevance of N=1 trials can be, and often is, better than most of what passes for science in nutritional “research”. That’s because the motivation for an N=1 trial is to discover what actually works (and doesn’t), and most nutritional “research” is for the sole purpose of figuring out how to sell an expensive prescription. At least indirectly. The direct purpose is to get more “research” funding.

    That’s how I chose the name for my blog…

  14. We have never had a TV or computer in our bedroom, nor will we ever have. We never let any of our kids ( all 4 now grown) have a TV or computer in their bedrooms.
    Our alarm clock radios are red lighted, not blue. And our bedroom and house fluorescent light bulbs are the full sun spectrum. Hmmm, I get plenty of rest, fall asleep easily, and never drink (nor need) coffee (caffeine) in the morning or during the day. Go to bed when tired whether 9 pm, 10 pm, or sometimes 11 pm.
    I guess not much to change. Oh and a candle on at night, in our bedroom, well TMI …..

  15. You didn’t specify the timing involved in avoiding blue light–always? sunset? 2 hours? 4 hours? I go to bed after the news at 11:30, read for a while until I’m sleepy and get up about 8 AM. The room where I spend the evening is also where I spend time during the day. We have blue light in hopes that it will be stimulating during the day. When do I need to switch off the blue light and switch on the yellow. I’m retired and the midnight to 8 routine seems to work well for me, but sometimes I do have trouble getting to sleep.

  16. I’d be interested to find out if there’s a difference between the effects of the emission spectra of incandescent vs CFL bulbs regarding this issue.

    1. Yes it is not just the colour of the light, but the whole spectrum. A bulb (e.g. LED or CF) that has a “warm” red or yellow colour, will nevertheless have narrow “spikes” in the blue wavelengths, and these will still trigger the blue receptors in our eyes (and apparently skin too) even if we don’t percieve it in the colour. There was a great article in New Scientist showing this: (subscription needed).
      Here’s a post from Scientific American:
      But I’m not sure about their “human vision” line on their graphs – as I understand it the eye has seperate receptord for specific colours.Only incandescent bulbs have the “black body” spectrum that contains only red-yellow colours – all of the other types have “emmission lines” i.e. spikes at certain colours. “black body” spectrum is also produced by fire and candle flames.

      1. Thank you.

        Thinking back to high school science when we used prisms to separate certain wavelengths from various light sources even though some may seem one color have the other wavelengths bundled with it. It more had to do the elements used to create the light.

        That also brings to question how well f.lux should really be working. As the source light hasn’t changed. Also if fliters such as those inexpensive “gel” filters for theater lights cut to shape or the filters sold by lowbluelights or even safety glasses.

        I suppose in our n=1 if it works for you and long term you show no signs of being low melatonin or what not. Then it works.

        Anyone to try to hack theater gels for screen filters or post eye exam style glasses? because i’m all for cheap 🙂

  17. I don’t know; theres an orange streetlamp RIGHT outside my window and I’ve found I sleep a hell of a lot better once I got some heavy curtains to block it out.

    Although it does make it harder to get UP cause i dont have natural light filtering through the thin curtains I used to have >.< Ive tried to compromise by hauling back the curtains in the early morning so i can taper awake a little bit more before my alarm goes off .

  18. I always wondered how Grok could sleep beside a campfire if we really needed total darkness.I knew it!!!

  19. What if, as far as lighting goes, you use regular old incandescent light bulbs and not LED bulbs?

  20. I use a full spectrum light box in the morning. By blunting melatonin earlier your body will begin to produce it earlier that evening. Also, melatonin gears down the brain and body primarily by slowing metabolism to reduce body temperature. Therefore, simply lowering the temperature in your house or taking a lightly cold shower helps.

  21. It is daylight right now as I write this and I am looking at my computer screen with white lights throughout the office trying to keep my eyes open and forcing myself to not fall asleep reading this article and all the comments. What does that mean?

    1. Blue lights don’t necessarily energise you, they can just bump along your circadian rhythm in either direction. ^^
      I can’t tell you the number of times I’ve been sitting around exhausted with a blue light box blasting at me. Although I actually have problems responding to blue light and my circadian rhythm isn’t entrained to anything, so who knows. :s

  22. I’ve been using the approximately $8.00 orange glasses for my nighttime reading for several months now (I read on an iPad, so it really helps with the blue light.) I get sleepy much faster using the glasses — even when I’m reading an exciting novel. They work great (got them on Amazon but they are referenced on MDA where I got the idea last year.)

  23. I have been experimenting (without record) with this. I read by candlelight a few nights a week, at least. I do believe I am noticing a difference in how early I feel sleepy and in how much more relaxed I feel when I wind down in this fashion. Not sure if I feel more rested or not…I think there are a few too many factors playing into that one!

  24. And I just installed f.lux the other night, but I am making an effort to not even look at the computer after ~10pm unless I must. I suppose I’ll comment on that if I observe any changes worth noting!

  25. I would like to give some of these experiments a try and see what effects they have on my sleep. I have been using a bedside of the Zeo Sleep machine which reads and records brainwaves. I have learned a lot about my sleep (how much light vs deep vs REM sleep) and how it is affected by how much caffeine or alcohol I drink (and when I drink it), the foods I eat, the time I go to bed, temperature of the room, etc.

    Definitely will try some of the things here to see – Self experimentation is fun!

  26. I’m always ready for an experiment. Heck, it’s what invigorates me most in life these days.

    So consider your challenge accepted Mark. I’m starting tonight and we’ll see how it goes after a week.

  27. I have to point out a very serious flaw in this experiment, fire, campfire or otherwise is a very recent invention and would not have affected early mans circadian rhythms as you suggest. All wild primates sleep outdoors and would be affected by blue light in a positive manner. If you have ever lived outdoors and away from the city you would realize the tremendous amount of blue light that is naturally available in the form of moonlight. In fact most nights are quite brightly lit and barring clouds or a small amount of time that the moon is in shadow, flashlights are not needed at all.

    1. the book “Catching Fire – how cooking made us human” by Richard Wrangham suggests a much earlier adoption of fire, around 2 million years ago, which would give plenty of time for adaptation.

      Good point about the moon tho’, I’ve wondered that one myself

    2. Actually, while moon’s reflected light is fairly blue very rarely is the moon’s light bright enouh to make a difference. I’ve lived outside for weeks at a time, and since the moon’s path to fullness is fairly parabolic, only for the three days surrounding fullness is it bright enough to make a difference, and only for a few months out of the year does the full month actually hit while the moon is up at night and also high enough up to make a difference.

      This is why programs such as Lunaception (women sleeping in total darkness except for the three days of the month surrounding the full moon) help to regulate our longer circadian cycles.

  28. Thank you, thank you, thank you! to the person who recommended f.lux. I just downloaded it and the difference on my computer screen is amazing! I use my computer a lot in the evening and I didn’t realize just how much that blue light was blinding me every night! Wow! It’s only been a few minutes and I already feel the difference on my eyes.

  29. Ditto on the f.lux. I heard of it here, although my brother swears he told me about it at least a year ago (I don’t remember), and it makes a difference for sure.
    As for the experiment, I used to go to bed very late, like at 2 am, but now am in bed mostly by 11:30 or midnight. What a difference that made. I am tempted to go to bed at 10 pm but it seems just too early for me. Might still give it a go though.

  30. For me, the best thing about flux is the way it reminds that night has arrived. My screen goes yellow….. Perhaps it is time to wind down the electronics.

  31. Himalayan salt lamps give a warm rosy glow, supposedly collect positive ions, and are low wattage, 15 to 25 watts. They even look very Paleo, especially the ones that are just piles of rocks with a bulb inside.

    I have been gradually replacing our regular lights with the salt lamps. I love the way they look and definitely give a candlelit feel to home life at night. You can read by them if you have one close to you and they cast just enough light to get around the house safely at night.

  32. “Is reading more stimulating than hanging out with your spouse?”

    That cracked me up! Wow, what could he be reading?

  33. What if you paint your walls yellow? I painted my house a shade of golden yellow (weak urine sample color?), and sort of get the same effect as a yellow bulb.

  34. Great idea…. but a little tricky at this time of year in Sweden… Midsummer’s Eve today, which is all about light 🙂

  35. Sorry to nit-pick Mark but ‘They’re got’ isn’t right. 🙂

  36. I love self experimentation and agree with mark that it is great for finding your way to health. I even like when everyone shares the outcomes of their experiments. But many people do an experiment and immediately tell everyone x is the way to do things because of it. They tend to forget that who knows you might be an outlier or there might be a confounding variable that you didn’t recognize. I would like to see more people have an awareness of the limits of their n=1.

  37. Don’t forget the lampshades, peoples – my lampshades are a light-to-medium brown, and at night they cast a lovely subdued golden light – very relaxing.

    Also, since I keep my home very dark at night after bed, on the rare occasion I need to get up in the middle of the night, I use a little electric tea light candle (also called flameless candles) that produces an orange light. It’s just enough light to see by since my eyes are already adjusted to the pitch black. In my experience, they are much less bright even than candles.

  38. I am a big believer in personal experimentation, and the first of June I started a 30 day experiment to not use any light but candles unless it was an unwise situation, like midnight poopy diapers on my 6 month old. I use a flashlight so I can properly clean bums. Anyway, I was concerned that with the little sleep I DO get (6 month old still up every 2 hours) I can’t waste time between getting in bed and falling asleep. My mind would be busy even though I was exhausted. I started changing how I did everything because I’m avoiding artificial light as much as possible. No more vacuuming at 9:30pm because there is not enough light to see. Now most of my chores happen early in the day. Anyway, I do fall asleep faster now.

  39. This is do-able. I can put all nighttime bulbs and a filter in our bedrooms and have the blue lights (always my preference for a lightbulb…most likely an inherent outside time craving) in the rest of the house.
    And is it blue light spectrum on the skin — or received in the eyes — or both? I always found going outside in the morning and letting the sun shine on my bare back for instance, even with eyes closed, was energizing.

  40. Would using regular sunglasses have an effect on blue light intake?

  41. Did this years ago. Look at for spectra of all sorts.
    He’s tested fLUX (screen still emits significant blue even set for very warm). He’s tested “warm white” bulbs (they emit blue). He’s tested the GE “Post Light Bug Light” — that’s a good one, almost completely blocks the blue emission with a yellow dome. And you can look for “Turtle Safe Lights” +amber +LED and find monochromatic amber sources, no blue at all.

    Distinguish color temperature; a warm LED or CFL still has a big spike of emission in the area below 500nm.


  42. You can buy removable & reusable iPhone, iPad, and tv filters on

  43. “Will Blue Light Affect Your Sleep? | Mark’s Daily Apple” was in fact a relatively good article, . I hope you keep authoring and I’ll try to continue to keep following!
    Thank you -Marianne

  44. Aren’t there receptors in the skin as well? I remember there was some experiment involving something like that. I’ve heard a lecture about lab animals mentioning similar and heard Rob Wolf mention skin receptors as well.

    Moon light of the brightest fullest closest moon on a clear starry night may seem bright but measures around 1 lux(about a candle) it just that it is very diffused making it seem brighter. Also according to photo sites it measures 4000k (color temp) making it visually warmer than sunlight. so intensity and wavelength make a difference.

    If I remember correctly (maybe not) he Lab animal lecturerer mentioned light of about either 5watt or 5 lux would disturb lab animals circadian rhythms and lead to raised stress in animals. drats to my sieve like memory. It must be all the low quality sleep.

  45. HELP! I live in the uk and I need to find a descent priced pair of orange sunglasses. I am not paying 80+ dollars and having it shipped over here for something costing 2 pounds to make in china.


      I bought the ~50% yellow and the 16% amber; the yellow does block blue wavelengths but allows much more total light through, so are quite unobtrusive. The amber ones are much darker, though you also get used to them pretty quickly. The non-fitover style fits the curves of your face pretty well to block out light from the sides, while the fitover style is less fitted but still pretty good.

  46. If you’ve got a Mac, you can use Candlelight. It removes the blue component of your Mac’s display. For more information, go to:


    is a page of spectra from various sources. Craig at LEDMuseum has checked most of what’s been suggested.

    The “post light bug light” has only a very slight emission in the range of 400-500+ nanometers that interferes with sleep.

    The amber LEDs (“turtle safe” or hallowe’en LED lights) have no blue at all.

    But the “warm” lights emit a lot of blue; so does your computer screen even using “Flux” — because those are driven by a blue emitter with a phosphor over it.

    We started this same experiment at home about five years ago. It works very well –as long as you don’t fool yourself. Don’t use logic. Get a spectrograph or look up the spectrum being emitted.

    It helps to understand how fluorescents of all types including “white LEDs” emit blue to drive the light and a layer of phosphor to shift some of that blue to longer wavelengths that seem ‘warmer’ — and that the blue still comes through which is what you don’t want for this experiment)

    You can buy filter material to block blue from any theatrical supplier. Again look at the spectra being blocked.

    You can look this stuff up.

    Some places to start

  48. I’m very aware of the effects of light during night and the sleep deprivation it causes, so the hour before going to bed I avoid tv, Pc, and turn on a very soft and warm yellow light.

    I think it’s advisable to use these features in a pc:
    – the high contrast yellow skin
    -the gooogle chrome add-on “change colors” I have already selected yellow for main text, orange por links and red for already visited links
    -and F. Lux, a free software that warms up your computer display at night, to match your indoor lighting by adjusting a computer display’s color temperature.

  49. Wonderful post however I was wanting to know if you could write a
    litte more on this topic? I’d be very grateful if you could elaborate a little bit further.
    Appreciate it!

  50. Hi,

    In addintion to F.lux software there is any other protection needed, for example any glasses or an screen for the monitor…


  51. I sleep early at 8 or lately 10 pm in winter. I want to sleep late. So if i use halogen bulbs does it affect my sleep ? Do i sleep late night with halogen bulbs while im studying or reading?

  52. > Derick wrote on May 9th, 2014

    I get a possible malware warning on that link behind the name “Derek” (the comment is vaguely botlike)

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