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

You guys ready for another personal experiment [8]? 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 [9], no drastic changes to your sleeping schedule [10]. 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 [11] 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 [12], 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 [13], to hunt, to gather, to build [14], to work [15], to exercise [16], to study, and so on. Secretion of melatonin [17], 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 [18].

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 [25]. 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.┬áSince 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.

Come up with a hypothesis, such as:

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

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

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 [27] 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 [28] on self-experimentation next week. Thanks for reading!