Most people are at least somewhat familiar with the concept of the circadian rhythm. Every living thing has a circadian rhythm—an approximately 24-hour cycle of biochemical, physiological, and behavioral processes. 

External cues called zeitgebers (what a great word, huh?) alter our rhythms, for better or worse. These cues keep us on track, or not, depending on the exposure. Powerful zeitgebers for humans include temperature, meal timing, social interactions, pharmacological interventions, and, most prominently, the light/dark cycle of the earth. 

Yes, light, or the lack thereof, plays an enormous role in the regulation of our internal biological processes. 

For millions of years, “light” (or darkness) always referred to the presence (or absence) of the sun. Once humans harnessed fire, we introduced some light where once there was only darkness; but the real, dramatic change occurred with the advent of electric lights. That’s when we could truly banish the darkness.

And when it comes to our sleep cycles, it’s been downhill from there.

Artificial Light at Night

You see, it’s not just natural light that affects our sleep cycle, but also unnatural, manmade light. Bright, blue light from a 10:00 AM sky. Bright, blue light from your computer screen at midnight. It makes no difference to our circadian rhythms. It’s all the same to our bodies. 

When light enters the eye, optical cells express a photopigment called melanopsin. Scientists think melanopsin is the primary regulator of the biological clock and production of melatonin. (In otherwise blind patients with intact melanopsin systems, blue light has a strong effect on their sleep cycles.) Exposure to blue light limits the production of melatonin, so we stay alert and awake; that’s what we want during the day. At night, an absence of blue light allows melatonin production to ramp up so we get sleepy. 

At least, that’s how it’s supposed to work, if we don’t mess it up (which we do). This system worked quite well for a long time. Reddish light from fire has little to no effect on melatonin production, so sleep wasn’t disrupted when we relied on fire. These days, though, we’re subject to a steady barrage of artificial light at night, and nighttime exposure to blue light disrupts our sleep hormones, period. (Is blue light the only issue? No. But it’s the biggest one.) 

Luckily, though, this is something we can largely control—even if we don’t always want to. 

Blue Light Exposure and Sleep Cycles

It’s really not that hard to limit artificial light at night (unless you’re a shift worker, of course).

• Keep electronics usage to a minimum after dark. 

• Enable night mode on any devices that offer it.

• Use candlelight, or swap out the white light bulbs in lamps you use in the evening for yellow or orange tinted bulbs. 

• Maybe wear blue-light blocking glasses. (I’ll talk about this in a future post.)