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Let me introduce myself. My name is Mark Sisson. I’m 63 years young. I live and work in Malibu, California. In a past life I was a professional marathoner and triathlete. Now my life goal is to help 100 million people get healthy. I started this blog in 2006 to empower people to take full responsibility for their own health and enjoyment of life by investigating, discussing, and critically rethinking everything we’ve assumed to be true about health and wellness...

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November 20 2013

Blue Light: Better Than Coffee?

By Mark Sisson
88 Comments

Blue LightFor years now, across multiple posts here on Mark’s Daily Apple, nighttime blue light has gotten a pretty bad rap. Although I’ve mentioned that blue light during the day is important (and natural sunlight is helpful), I haven’t focused on it, mostly homing in on the circadian-disrupting, sleep-inhibiting, melatonin-blunting effects. As a result, many of you may be entirely unaware of the potential positive, beneficial applications of blue light. Recent and not-so-recent research has confirmed that blue light can actually improve our cognitive abilities, including memory, alertness, reaction time, and executive function – at least in the short term.  Oh, and it doesn’t always ruin our sleep. It might even improve it if you expose yourself at the right time.

Wait a minute – blue light is good for us? Sisson, you just got done spending the last few years telling me to excise blue light from my vicinity at night if I wanted a good night’s sleep, and now you’re saying we might actually need more blue light. What gives?

Easy. Context is everything. Blue light at night can have a negative, inhibitory effect on our sleep onset and sleep quality because it signifies daytime to our suprachiasmatic nucleus, that region of the hypothalamus that sits near the optic nerves and regulates our circadian rhythm according to the light we perceive. But during the day – you know, when blue light naturally bounces around the atmosphere into our eyes – it’s beneficial because presence of blue light matches up with our bodies expectations. Blue light isn’t “bad,” in other words. It’s bad in the wrong context. In the right context, which is daytime, blue light promotes restful, satisfying nighttime sleep.

And for the exact same reasons blue light is bad for melatonin secretion and sleep physiology when we’re exposed at night, it also provides a boost to cognition. The bulk of the blue light research may focus on its inhibitory effects on melatonin and sleep, but a growing body of study is realizing that those same inhibitory effects seen at night can be used to improve alertness, executive function, memory, and other aspects of cognition. What’s negative at night when you’re trying to sleep is helpful or even essential when you’re trying to get work done. Blue light may very well be better than (or at least equal to) caffeine.

Let’s look at a few recent studies to see how we might use blue light to our advantage.

  • In this 2011 study, LED backlit computer screens enhanced cognitive function to a greater extent than non-LED backlit screens. Sustained attention, working memory, and subjects’ ability to learn words were all enhanced in the LED group. Both screen types emitted light of the same wavelength, but the LED screens’ light was over twice as intense.
  • A recent study (PDF) compared the effects of caffeine and blue light on psychomotor function (the interface between cognition and physical movement) and found them both to be positive but distinct from one another. Subjects exposed to blue light performed best on tests of executive function that included a distraction; the same distraction proved too distracting for caffeine users, who fared more poorly. Both groups performed well at a Go/No-Go test, which assesses sustained attention.
  • Even visually-blind people with “non-image-forming photoreception” (the ability to sense light) derive cognitive benefits from blue light exposure, according to a recent, very cool study. fMRI tests confirmed that brief exposure to blue light “triggered the recruitment of supplemental prefrontal and thalamic brain regions involved in alertness and cognition regulation.”
  • Still, the best way to get your blue light is probably through natural daylight. A 2011 study (PDF) out of Switzerland compared the cognitive effects of daytime natural light and daytime polychromatic (which includes blue) artificial light. Subjects were exposed to six hours of either light source from noon onwards and subjected to a test measuring executive control. The natural light group was more accurate and made fewer errors. Melatonin secretion were similar in both groups even though the natural light group was more alert.
  • Cognition-enhancing blue light during the day also has the likely effect of improving sleep at night. In 2008, researchers improved alertness and productivity in office workers by switching out their standard fluorescent white overhead lights for blue-enriched white lights. Blue-exposed workers performed better, which was expected, but they also slept better at night (which undoubtedly helped performance).

Not bad, eh? Makes a guy want to step outside and get some fresh air. Or, barring that, stare straight into an LED bulb.

Things to keep in mind when applying these results to your workday:

  • Use an LED. Most of the studies used basic LED lights. Others may work, but we know LEDs work. The caffeine/blue light study used a 3-watt, 470 nm, 40 lux RGB LED bulb, similar to this $2 one from eBay. This is another option.
  • Or download a blue light therapy app for your smartphone. iOS has Blue Light Therapy and Android has Blue Sleep Therapy. Turn the brightness up.
  • It doesn’t take much exposure to get an effect. Although the caffeine study used hour-long light exposure times to match the known duration of effect of caffeine in the body, other research has shown changes to brain function with just 50 seconds of blue light exposure.
  • Get blue light freely during the day. We’re supposed to get lots of blue light during the day (natural daylight is filthy with it), and the research is pretty unequivocal: blue light exposure enhances cognition and alertness during the day. Ideally, we’d get it from working outside, but artificial blue lighting works too (that’s what they use in the studies). Don’t worry about any negative effects, because there shouldn’t be any (unless you’re a shift worker trying to get some sleep).
  • Residual effects on sleep may linger, so time your exposure accordingly. In the natural light study, subjects were exposed through 6 PM and alertness persisted after dark.
  • Use it judiciously at night. Up against a deadline or driving late at night? Turn off the f.lux and hit yourself with the full dose of blue light. Browsing forums and checking email? Don the blue-blocking goggles and avoid it. Since it’s still going to disrupt your circadian physiology, only use the blue light at night if you really have to.
  • You may not notice anything new if you work on a computer with an LED display since you’re already getting a fairly steady dose of blue light from the screen. One way to test this is to use your computer (without f.lux or goggles) at night. If your sleep is disrupted or you get sleepy later than usual, it’s likely boosting alertness when you use it during the day.
  • Don’t ditch the coffee, necessarily. Coffee and blue light can have synergistic effects on cognition and mood. Plus, coffee is delicious.

So, in the end, blue light isn’t a villain. It’s just misunderstood (and misapplied).

How are you going to use blue light to your advantage? Or are you already doing so?

Thanks for reading, folks. See you next time.

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88 thoughts on “Blue Light: Better Than Coffee?”

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  1. think i’ll just head outside for my cup of ‘blue light caffeine’ 🙂
    thanks for the research mark, always appreciated.

  2. My desktop picture is a big blue sky above a rural landscape, and I have flux installed. Sorted.

    (I wonder if that’s why I was drawn to having a blue desktop?)

      1. I know it’s a bit late but you have to jailbreak it as F.lux isn’t available on iOS devices.

  3. It would be interesting to study the side-effects of wearing 3D glasses (the red and blue ones).

  4. A quick search says using red light bulbs before bed can help your sleep.. perhaps that has some merit!

    1. That’s very true for me, Ben. I’ve been looking into the whole sleep/circadian rhythm thing for years to help with insomnia and I now use red light bulbs at night exclusively upstairs. I keep one next to me for reading or watching a little tv (the tv is kept as dark as possible, and I wear glasses to block out even more blue light. I also keep a small red night light in the bathroom till I get to bed, then it’s almost total darkness if I have to go again in the middle of the night…Been sleeping great since making these and other sleep hygiene changes.

    2. I have a red night light for my son, perhaps I will have a blue one for morning.

  5. Question on F.lux. I notice the change in my screen at night as it dims according to the sun. I assume that this the beginning if blocking blue light. I assume it’s letting blue light in prior to that?

    If not il turn it off during the day. Thanks

    1. Yes, f.lux only dims blue light in the evening. If you ever spot your computer through the window the difference between red/blue is very apparent.

      1. Okay cool, thanks. Interesting I’m gonna go look at it through the window tonight lol.

    2. You can turn it off temporarily during the day, but I don’t think you’ll notice much (if any) difference. At night on the other hand is a whole different story.

    3. Go to the preferences and change the settings to control the degree of Blue during the day and orange at night. You can make it whatever you want.

  6. I do every morning in this order: Coffee -> food -> shower -> Blue light (phillips goblue). I’m wide awake by the time I get to the end of it.

    1. Make that a cold shower and it’s sounding a bit like my routine! (although I’m on a yerba mate kick as of late)

    2. Hi mate,

      Wouldn’t be better to eat a little before having coffee?

      1. I actually do, but only a little. Usually I’ll have a bit of carbs and protein (not much), then drink a cup of yerba mate, followed by an intense, heavy workout. Of course, at this point I need a pretty substantial amount of calories, followed by cold shower as a prerequisite for an energizing day.
        Cheers!

  7. Love it, simply love it! There had been a lot of confusion on this subject lately, so I’m glad that you’ve brought the light (blue one) upon us!

    Sweet!

  8. You ever pull an all-nighter driving (really not recommended, but I think most of us have done it once or thrice!), and then notice that second wind as the dawn is in full swing? That makes a lot of sense to me now!

      1. Worst name for an app ever! Lol. If anyone can post a link to the app, I would love this on my iphone. I can’t find it in the app store (good luck with a search for the name ‘twilight’!

        It seems like there’s an android version readily available, but I can’t find it for ios.

  9. I hate to post this but…..how much CONTROL must we really have over every tiny detail anyway?! I’m all for educating ourselves…but this is slithering towards complete and utter navel gazing…using a microscope, no less. (I say this with a chuckle) I think this level of control over the smallest details is what gives the overall Paleo community a bad rap. Again, kind of hate to point that out, but I’m grimacing reading this. I picture someone with their special lighting routine (which is all part of their 98 point plan for how to use technology to revert back to caveman!) and they FREAK out if the blue lights are left on too long! too Loooooong!!! argh! I’m sorry, don’t want to be negative, but this just strikes me as a little funny.

    1. Interesting read but I too can’t help feeling you’re more likely to lose sleep (at night) or alertness (in the day) through stressing over these minute details. So the UK isn’t beaming with natural sun for many days of the year but I’ve got through life so far.

      Perhaps more interestingly, I read that caffeine can have a half-life of upto 6 hours in our body, so I will continue to follow simple rules like not consuming caffeine after 3pm most days!

      1. Luke, apparently it’s not necessary to have sunlight (I live in Canada, so I know where you’re coming from). Just looking out the window or being outside for a bit–even on a very cloudy day–allows a great deal of this ‘blue-light’ into our brains to keep the circadian cycle running well 🙂

        1. The sun isn’t necessary, however the sun is brighter than any light source you’re likely to have access to. Hence why sunlight is preferable to artificial.

          That being said, the area of the spectrum you get benefits from is relatively narrow and the sun includes all sorts of radiation that isn’t involved in that.

          What’s interesting is that it’s not just the light, but the body temperature that has an impact here. I’ve been experimenting a bit, and if I exercise at like 9 in the morning, I definitely sleep better in the evening.

    2. If you find it uninteresting, then don’t bother yourself with it, period. I for one am interested in mark’s scientific minded articles, which is why subscribe to his daily apple. I don’t even eat the primal diet, I just like smart people, Emily

    3. LMAO. Using technology to get back to caveman. I love it. In the most positive way possible, I say this….I agree with what you are saying.

    4. It is funny to some people, however, those of us who are suffering from a lack of light at the right times or too much at the wrong time are grateful. Many nights of no sleep are really boring as well as unhealthy. Some of us have bodies that are waaaaaaaay too sensitive to changes in light (sad face inserted here).

    5. The info is always useful. I keep a very soft blue light in my younger son’s room at night because he’s afraid of the complete darkness but getting this info I will definitely change that. Plus, most people on MD just love the research, and I for once am pretty aware that research results are not for ever! It doesn’t mean we are perpetually fine tuning every aspect of our lives to match the recent research results but as I said, information is power.

    6. Suzanne – I hear you. If you’re mucking around here or in a million other places, you’re searching and exploring for information to tinker and improve your life.

      I jumped into this paleo stuff four or five years ago and you can go nuts trying to follow and figure it all out. Good news – you don’t have to. I’m not suggesting that you are saying that. And some people might freak out as you say.

      This paleo or general health stuff is a huge kitchen full of ingredients – Mark’s place is a cool cupboard of stuff. We’re all just mucking about, testing our cooking every day. What works for one person may not for the next – and you can’t use every ingredient – at least not every day.

      A person’s thoughts and attitudes have a lot more impact on health and well-being than anything you expose your body to – so chill – enjoy the ride. And have a lot of fun in the kitchen. We’re all gonna cook our ingredients a little differently – that’s what makes this all so fun. You are here for fun I hope. Fun beats any color of light or any kind of food or exercise – its the essential ingredient.

    7. I see it as taking back control over my lifestyle choices. My employer decides what kind of lighting to have in our office; the retailers I go to decide what kind of lighting to put in their stores; I was born into this modern era without my choosing, etc; and so on any given day, I have pretty much surrendered control over this aspect of my lifestyle (and over many other aspects as well). I’ve opted into society, so I’m willing to make some trade offs; still, it doesn’t feel good to me that suboptimal choices are being made for me. The quality of light that I receive affects my well being, and I didn’t really get much say about it. It’s empowering for me to know that I have a better choice, should I want it. So maybe I’ll get a blue light at my desk, and maybe I won’t. But I don’t see how spreading quality information about health, which is what Mark is doing, is a bad thing.

    1. Not necessarily. Think of a missile “honing in” on its target. I believe both are acceptable, but I’ve seen “hone in” more than “home in”.

      1. Your example is incorrect. A missile “homes in” on its target. Just because a mistake is a common one does not make it acceptable.

        1. That’s exactly how that works. The original meaning of nice was decidedly un-nice and molest meant something very different in the past.

          Language lives, and while honing in isn’t correct at this stage, it could well become correct in the future.

        2. hedwards is exactly right. Much as it galls me… Language change is inexorable and inevitable, and English is already littered with words that were once common errors.

        3. Err, to be clear, the fact that misuse becomes acceptable use galls me.

      2. Missiles home in. The phrase is derived from the behavior of homing pigeons.

        Honing is the process of sharpening a blade. Used metaphorically, it means to sharpen, refine, perfect through training, as in “007’s fine honed reflexes” or “Wilde’s well honed wit.”

  10. As I wake up in the morning, I walk threw the house flipping on every light by the time I let the dog out and start a fire the house is bright as day. I am almost up to worp speed by the time I get my first cup of tea.
    By about 5;30-6:00 the lights are being turned off or are orange. All lights are out by 9:00 pm.

  11. Mark, what would my life be life without you? THANK YOU!

    This time of year, I have “9 o’clock narcolepsy.” I sit down on the couch in the evening and I cannot stay awake. Doesn’t happen in the summer at all. Then, I’m fully awake by 5:00am, which is way earlier than I want to get up, especially on weekends. Sitting in an afternoon sunbeam helps, if I’m consistent. From Thanksgiving until March, Washington DC is cold, gray and rainy, so it only works until then. Can’t wait to check into blue light options.

  12. I work in an internal room with no natural light. Last year my hours switched from 6-2 to 8-4. No longer getting afternoon playing with kids outside, and I was constantly feeling drained. My manager got me a high end blue light for my desk a few months back. Immediate effects on energy, attitude and emotions. Works wonderfully.

  13. Interesting article. I am not nearly as drowsy during the day since increasing my light/sun exposure during the day & decreasing it at night. Seems to be slowly changing my body composition in a positive way too. Hoping that the sun doesnt hide too much this winter!

  14. I use a Litebook Elite in the morning. It’s been tested for potential damage of the retinas, and has been shown to be safe.

    This is a good site. Here he talks about the safety and differences between various wavelengths of light and their potential therapeutic value:

    http://winterbluescoach.com/white-blue-green-light

    For general lighting at night, I use an amber LED bulb that I got from lowbluelights.com, and I also got a couple of their flashlights. Amber lights in general are my preference for lighting at night.

    Richard Hansler wrote a book called “Great Sleep! Reduced Cancer!” that gets into some interesting stuff with the science behind blue light. It was only 12 years ago that blue light was shown to be specifically involved with suppressing the pineal gland’s secretion of melatonin. I only use non-amber lights at night when I’m trying to extend my wakefulness, as in the winters here in New England. Outside of that, I either wear blue-blocking glasses at night (inspired by Chris Kesser’s article about artificial light and how it’s wrecking our sleep), or use all amber lighting. I always use f.lux and they recently updated it to include far-red spectrum 1200K lighting and a Darkroom mode for even more elimination of blue light.

    For the dark New England winters I use a clear 250W heat lamp bulb in a 10.5″ brooder clamp light from around 4:30-5:00PM to 8:00PM, to emulate the light exposure that we usually have around August/July.

    At night, the 250W infrared heat lamp bulbs work very well, although like I said earlier, I prefer the amber LEDs.

    I prefer using the infrared lamp for therapeutic use, although I will use it for general lighting sometimes too. Infrared light has been shown to be able to penetrate the skin and stimulate the cells to produce ATP, which can speed healing and might offer some promise for things like arthritis, tendinitis and other inflammatory conditions. 660nm and 850nm LEDs seem to show the most promise.

    This is a very good site on the benefits of red light. It’s focus is the therapeutic value of red LEDs:

    http://heelspurs.com/led.html

  15. Mark,

    The Android app’s description says this:

    “The illumination rises and falls over a customizable time period slowing and dimming to a gradual power-off. The cycling encourages breathing patterns that lead to a faster more relaxing night’s sleep… But research has shown that the use of blue light before bed and upon rising can promote the reset of your body’s Circadian rhythm, necessary to sleep through the night and ward off Seasonal Affective Disorder.”

    Since what you are suggesting is that use before bed is NOT what we are going for, I am assuming you mean whatever function they offer is useful for waking up instead of going to sleep?

    Thanks for any info.

  16. I am finding that with the seasonal change a blue light is really helping me to awaken in the morning (as well as my mood). When I wake up, I now turn on the lamp right away. The light seems to alleviate the desire to stay in bed, hit “snooze” (or reset an alarm), etc. I have a pretty good light. It’s actually a model for people with Seasonal Affective Disorder (SAD). A social worker recommended buying one a few years ago, then I forgot I had it after storing it for the off-season. Really does seem to help with my mood as well (since not as much available sunshine now). My father seemed to get grumpy during the winter, so I have to wonder if I inherited some tendency for SAD.

  17. I wonder if we can use the f.lux program to make out computer screens even MORE blue for even more awakeness….

  18. So now we know why Microsoft picked the background color of a system crash. It makes you think more when you need it. Thank you blue screen of death ;).

  19. I don’t know that it’s “obsessing” necessarily to take these ideas into account, especially since implementation is easy – download f.lux, set brightness and sunset time…and then done. Just moved my “daytime” setting to full daylight. Holy cow is it bright, I didn’t realize how much my eyes had adapted to a lower setting. Anyway, the switch today took approx 15 seconds.

  20. These dark days of winter have me turning on bright lights in most rooms in the mornings and at night time to keep me awake past 7PM. I don’t mind falling asleep at 7:30 of course, it’s the waking up at 12:30 for the day that doesn’t work well for me. Everyone else is alseep for another 4 hours in our house.

  21. Try switching out my coffee with a blue light and I’ll stab your hand with my cream covered spoon.

    1. I always like reading your comments Nocona! Laughed out loud at work.

  22. So, maybe car companies could add a blue light “alertness” setting to our dashboard instruments. Would be helpful for longer night drives. Drowsiness is just as imparing as drunkennes.

    1. My son’s car has a radio display that switches displays every minute or so from a dark background to an extremely bright blue. The first time I drove it it was a bit alarming, but it soon occurred to me that it was actually a safety feature, & I was grateful!

  23. Isn’t it interesting how virually all clock radios you can buy have white to blue light? Just try to find a red one! I finally, after pages of searching, found one on Amazon for about $20. Is it a conspriacy?

    1. I have a typical blue-light clock radio, but I put some deep red photographer’s gel over the display, & found it definitely helped me get back to sleep when I woke in the middle of the night. Red cellophane (cheaper) might do the trick if you use more than one layer.

  24. I don’t know if this is the same but I have been using full spectrum lights in my home for years to combat seasonal affective disorder. Where I live in Canada, at this time of year, there is only sunlight from 8am to 4pm and if you are working indoors all day, you don’t have much chance for seeing the sun.

    A boyfriend recommended the full spectrum lights several years ago when I was living in a basement suite and working in an office with no windows. I was so exhausted and depressed. Back then I used full spectrum incandescent lightbulbs which were tinted blue. And they helped quite a bit.

    These days I am fortunate to be working and living with large windows and lots of daylight but still only for 8 hrs a day at this time of year. I use full spectrum CFL’s and I much prefer them in the evenings to traditional soft white bulbs which I now find overly yellow and glaring to my eyes, giving me a head ache. The full spectrum is clearer, shows colors more like they look in real daylight and is softer.

    I admit that I do still sleep better in summer when I am up at dawn and going to bed just as the sun sets around 10:30pm, but with the bluish full spectrum lights in the winter, I sleep much better than I used to.

    1. I am in Canada too Kristen. I love my blue light but I wrote the company and verified it won’t stimulate vit D production so I still supplement that. You might want to check???

      1. Oh Terry, I for sure supplement with vit. D as well. It never occurred to me that I might get any from a lightbulb.

        I just find the full spectrum lights help me to prolong the feeling of daylight in the evenings.

        In the summer, I basically get up with the sun and go to bed when it sets. In fact during the longest days, I rarely see the dark.

        But in the winter, it’s dark when I leave the office at 5pm, I lose the sense that dark = sleep so I either feel like going to bed at 6pm or I ignore that impulse and then find I begin to lose all sense of night and day and stay up until the wee hours and not have any kind of internal sense of when to sleep.

        For whatever reason, having full spectrum lights feels more like I am prolonging daylight in the evenings to approximate summer vs. regular soft white bulbs which seem to compound the sense of artificial time. It could be 6pm, it could be 3 am, my body can’t tell the difference. It may just be psychological. 🙂

        But yes, I think everyone living in dark winter climates needs more vit. D. Even those who do lots of outdoor winter activities as you are still so bundled up, your skin doesn’t absorb enough sunlight.

  25. And for nocturnal people who can easily sleep until noon, is the brain different? Maybe less sensitive to visual cues? Maybe there is an overlap in people who are nocturnal and those who have sensory processing issues…

  26. Loved this article. The importance of bright light exposure in the morning (sun or otherwise) and lack of bright light exposure in the evening are not “minutiae.”

  27. I use a blue light first thing in the morning (while I work out) to get over jet lag faster. I reteach my body/brain when daytime is supposed to work. I travel yearly to Africa and have found this technique helpful. Grok on!

  28. Ok, so who knows the Windows background color code I can set my PC to so I’m bathed in wonderful brain activating blue light?

  29. I am interested in the app for android but I am concerned about radiation from my phone, I currently turn it off at night. What is the research on EMF and the primal life.

  30. Read about John Nash Ott and his studies on “Full Spectrum Lighting” (that included ultra-violet) and how it affects the penile gland in the brain. As noted somewhere above, natural lighting, is better for you than simply blue light.

    Having said that, I’ve wondered if the effect of warmer light reflecting off of a lot of blue surfaces, walls… furnature… reading material, (and hence removing the lower colour temperature spectrum/warm wavelengths) would act similarly. It seems logical that it would.

    Nice article but I would be nice to do one on John Ott’s studies. 🙂

    1. IN ADDENDUM… I guess that blue walls, furniture and reading material would only work if the originating light was full or wide spectrum AND bright enough, because blue reflective surfaces are in fact removing the warmer part of the spectrum, not adding blue.

  31. I am going to explore this idea as a supplement to my ADHD treatment. I have a large office window, but ’tis very cloudy and rainy in my part of the world in winter. Overhead in the office is quite a lot of light, but its flourescent and pink-ish. How interesting it would be if blue light helps improve my executive functioning!

  32. coffee is not delicious and never will be. it’s distgusting and we drink it only to get awake. don’t lie

    1. Nope. Love the taste. I don’t like much sweet stuff, so I love my coffee very dark and strong. Grassfed heavy cream sometimes whipped up with a frother and coffee poured in–delicious in afternoon.

      Best to you this holiday season.

  33. improve our cognitive abilities, including memory, alertness, reaction time, and executive function – at least in the short term. Oh, and it doesn’t always ruin our sleep. It might even improve it if you expose yourself at the right time.

    Wait a minute – blue light is good for us? Sisson, you just got done spending the last few years telling me to excise blue light from my vicinity at night if I wanted a good night’s sleep, and now you’re saying we might actually need more blue light. What gives?

    Easy. Context is everything. Blue light at night can have a negative, inhibitory effect on our sleep onset and sleep quality because it signifies daytime to our suprachiasmatic nucleus, that region of the hypothalamus that sits near the optic nerves and regulates our circadian rhythm according to the light we perceive. But during the day – you know, when blue light naturally bounces around the atmosphere into our eyes – it’s beneficial because presence of blue light matches up with our bodies expectations. Blue light isn’t “bad,” in other words. It’s

  34. I use 100W blue incandescent ‘craft’ bulbs throughout my home in an attempt to replicate the natural light spectrum. Also a ‘daylight’-white fluorescent tube in the kitchen. Are these the best solution?

  35. Mark, are we ruling out the D-3 we get with lots of sun exposure? Doesn’t D-3 also make you sleep better?