The above picture from space shows our current nighttime reality. 54 percent of the world’s population lives in urban areas — the major source of this severe light pollution — and that number is expected to grow to 66 percent by 2050.

Research has found that 80 percent of the world’s population lives under light-polluted skies. If you narrow this down to just the United States and Europe, the number climbs to 99 percent. The virgin night sky is now so foreign to the majority of individuals that it requires going to a very remote area or a major event like a blackout to experience the night sky as intended.

Before and during the 2003 Northeastern blackout, a massive power outage that affected 55 million people.

The light landscape changed drastically in a very short period of time. Instead of sunlight during the day and darkness at night, most of us are bathed in artificial light almost 24/7.

Notice the natural, full-spectrum curve provided by the sun and the unnatural peaks and valleys of artificial light sources.

What colors are now most prevalent? If you compare the visible spectrum reference chart below to common artificial light sources above, you’ll notice we’re getting a unbalanced surplus of violet, blue, and to a lesser extent, green.

Most artificial light sources peak in the 380–495 nanometer (nm) range.

Popular devices like iPads and iPhones feature these same peaks in the violet (380–450 nm) and blue range (450–495 nm) that we see from other artificial light sources.

Melatonin: The Chemical Expression of Darkness

90 percent of Americans use light-emitting electronics within one hour of bedtime. Exposure to violet, blue and even green light (495–570 nm) after sunset has two primary effects: melatonin suppression and phase shifting or re-tuning.

Let’s cover melatonin first. As noted in the section above, melatonin helps regulate sleep. It should be obvious, but it must be stressed: we are meant to have complete darkness at night. Cell phones, tablets, TVs, overhead lights, lamps, LEDs, etc., are not natural.

This is why studies continually find that violet and blue light suppress melatonin production the most. For example, something as seemingly innocent as room light can reduce pre-sleep melatonin levels by 71.4 percent and daily melatonin levels by 12.5 percent. This suppression effect is much greater in children than adults.

As the bar chart on the right shows, children (left bar) are more affected by the melatonin-damaging effects of artificial light than older teenagers and adults (right bar)

As you move further away from violet and blue (380–495 nm) toward green (495–570 nm), yellow (570–590 nm) and orange (590–620 nm) spectrum, the melatonin-suppressing effects aren’t nearly as great. Green light is about one quarter to one half as potent as blue, and yellow, orange and red have next-to-no effects on melatonin.

The X-axis is the wavelength. The dots represent melatonin effects— the higher the dot, the more the nanometer of light effects melatonin. As you can see, blue has the worst effects and then it begins to taper off with green and becomes minimal to non-existent once you reach yellow, orange and red.

If you’ve been clicking on the research links, you’ll notice several mention the term “lux.” This is shorthand for saying the total amount of visible light present and its intensity on a surface. The higher the lux, the more intense the light source.

Common light sources and lux values.

Complete darkness would be zero lux. As you can see above, something like a night without a full moon is only 0.002 lux. Compared to a moonless night, a typical living room light is 2,499,900 percent more intense. No, that number was not a typo.

Combine intensity (lux) with these violet, blue and green ranges (380–570 nm) and you’ve got a potent cocktail. Higher lux values amplify the damaging effects of these nanometer ranges. That’s why — if you go back to the previously cited study — you see a 301 percent increase in melatonin suppression between the 15 lux and 500 lux control groups.

This chart reinforces that it’s not just about the nanometer (nm) range, but lux value, too. A candle only has a lux of 10 whereas something like a LED can have a lux value in the hundreds or thousands.

When melatonin levels are disturbed and start to drop, the sleep/wake cycle is thrown into disarray and your body can’t properly utilize autophagy —an essential cellular maintenance and cleanup process. Melatonin is critical not only for this sleep/wake cycle, but the hormone itself

Given the melatonin-suppressing effects of violet and blue light, it should be self evident that if you block that range of light (380–495 nm) from hitting your eyes, you help preserve melatonin levels and thus keep sleep/wake cycles in order.

And that’s exactly what the research finds. Keep in mind: most of these studies only look at glasses that block violet and blue (and some green). We would expect glasses that additionally block all green to have even more benefits.

The dark line represents those that wore blue-blocking glasses whereas the grey one is those that wore clear lenses. Notice the sharp difference in melatonin levels between the two groups.

Excuse Me: What Time Do You Have?

When your circadian rhythm is running correctly, you can say you have a normal phase response curve. However, as you learned in the previous section on melatonin, violet, blue and green light start to shift sleep/wake cycles.

Organisms are so sensitive to light that just a single pulse of the wrong kind of light can initiate a process called phase shifting or re-tuning. Like with melatonin suppression, the greater the lux, nanometer range and length of exposure, the greater the phase shift.

The developers of f.lux, a light-blocking software, have a handy tool called the f.luxometer that calculates the phase shift potential of different light sources.

A device like an iPad Pro can easily shift your body to think it’s over an hour and a half “off.”

You may be thinking, “Well, I bet it takes days, weeks, months, heck, even years, before you start to see changes at the genetic level from artificial light and phase shifting.”

Sorry to burst your bubble. As noted in the introductory section, every cell is connected to time and the greatest environmental time cue is light. We’re so wired to pick up light, that we can detect a single photon. And all it takes is one night of artificial light throwing off your sleep to alter CLOCK genes and, in turn, affect gene expression.

How do we combat this phase shifting? Per the melatonin section, any kind of barrier — like blue-blocking glasses — that stops 380–570 nm of light will help preserve melatonin and help normalize circadian rhythm. If trying to keep things dark (or as close to dark as possible) during the night helps, then the corollary should be true, i.e., sunlight during the day should help, too.

That’s exactly what Environmental Health Perspectives published:

When people are exposed to sunlight or very bright artificial light in the morning, their nocturnal melatonin production occurs sooner, and they enter into sleep more easily at night.

This should not be misinterpreted to say, “Any light is good during day.” It depends on the type of light. The above quote notes the importance of sunlight, which has a balanced spectrum. (Remember the chart from earlier?) Humans have lived under the sun’s influence for 200,000 years.

Indeed, research shows that when groups are exposed to daytime artificial light sources that are warmer and more balanced (less blue) and light sources that emphasize primarily blue, the warmer light group has circadian rhythms that more closely match the rising and setting of the sun whereas the blue light group gets entrained to unnatural rhythms:

The results confirm that light is the dominant zeitgeber [environmental cue] for the human clock and that its efficacy depends on spectral composition. The results also indicate that blue-enriched artificial light is a potent zeitgeber that has to be used with diligence.

The Eyes Have It

One last biological stop before we nerd out on blue-blocker glasses: your eyes. First and foremost, you have to understand how you see the world.

Visual perception occurs when light in the 380–780 nm range hits the retina. Ultraviolet and infrared wavelengths aren’t absorbed the retina, but by the outer layers of your eyes — the cornea and lens.

The retina is responsible for the visual portion of the spectrum. The cornea and lens filter out the low- and high-nanometer ranges.

As you may (or may not) remember from science class, the retinas of your eyes are packed with rods and cones. These absorb photons and convert them into neurological signals for your brain.

Within the retina is a light-sensitive protein called opsin. When photons hit the retina, opsin combines with other molecules to start a series of photochemical reactions, which create retinal molecules that are either stored in an area called the retinal pigment epithelium (RPE) or combined with opsin again to complete the visual cycle.

The reactions that make up the visual cycle.

That area just mentioned — the retinal pigment epithelium (RPE) — is very important to our discussion moving forward. While RPE cells aren’t photoreceptive, they make sure visual pigments can regenerate and that photoreceptors survive and function normally by providing nutrients and oxygen, as well as help remove oxidized (problematic) cells.

While RPE cells don’t initiate the reactions that make the visual process happen, they do protect molecules that allow it to happen. That’s why once RPE cells start to take on too much damage, you get diseases like macular degeneration, and if enough cumulative damage occurs, blindness.

Some portion of blue light is vital to life. If it wasn’t, it wouldn’t be part of the sun’s spectrum. In fact, a photopigment called melanopsin targets the SCN to set the circadian clock. Research indicates melanopsin is most sensitive to 480 nm, which is near the end of the blue light spectrum.

How much blue (in particular, 480 nm) do we need during the day to set our clocks? More research needs to be done, but it appears as little as 30 minutes of sunlight helps with sleep quality and hormone responses, as well circadian timing.

Remember how in the section on phase shifting, we went over that not all light during the day is beneficial and that it’s better to get sunlight or try to mimic the sun rather than use blue-enriched light? The same holds true for eye health — in particular, RPE cells — regardless of time of day.

RPE cell apoptosis (death) is greatest in the 415–455 nm range.

The above chart is extremely important. It shows that at all times violet and the beginning of the blue spectrum have an extremely phototoxic effect, i.e., exposure to light in that range is particularly effective at killing RPE cells.

Knowledge of this light range on retinal damage goes back to 1966. In fact, this problem is so well known in many research circles that it’s called the blue light hazard. Recent research has highlighted this same problem area, noting:

An emission peak of around 470–480 nm should be preferred to … an emission peak below 450 nm.

The obvious connection to too much damage to RPE cells we covered earlier, and that is macular degeneration. There is also one other, very significant area impacted by violet and blue light destruction of RPE cells: docosahexaenoic acid (DHA), more commonly known as the most effective portion of fish oil.

Photoreceptor cells in the retina have the highest DHA content of any cell type. And since RPE cells protect photoreceptors and actively consume DHA, it’s easy to see that if destroy RPE cells, you destroy some of your body’s greatest DHA stores.

DHA is necessary to maintain RPE cell health.

But why should we care about DHA? Not only might DHA be necessary to completing the visual cycle, i.e., allowing you to see, but research continually finds that DHA “may indeed have a special place in biological systems.”

What makes DHA have a special place? It has been “the dominant fatty acid … for all 600 million years of animal evolution.” In fact, if we don’t get enough fatty acids, a syndrome called essential fatty acid (EFA) deficiency kicks in.

While there are many essential fatty acids, guess which one alone can completely obliterate EFA deficiency? That’s right: DHA. Not only can DHA help lower blood pressure, but it can increase the release of adenosine triphosphate (ATP), which allows more chemical energy to be made available for all cells.

Given DHA’s critical place in our biology, it makes sense the upping levels helps with conditions like high blood pressure. As noted earlier, the retina has the highest concentration of DHA. Therefore, we would assume that if we keep DHA levels topped off, we would should be able to better prevent RPE-damage-linked conditions like macular degeneration, and that’s exactly what the research shows.

The DHA-retina link to circadian rhythm can be found in proteins like rhodopsin, which convert light to electrical signals in the retina, that in turn talk to the SCN. DHA enhances and protects rhodopsin whereas blue light:

Bleaches the vast majority of rhodopsin, especially at night, [and] can overwhelm the photoreceptor’s capacity to prevent damage.

Before moving on, it should be noted that DHA found in seafood is superior to fish oil capsules because it is not only less prone to oxidation (it’s more stable), but is better absorbed in your intestine (it’s more bioavailable) and more easily reaches your brain.

Now, it’s finally time: let’s get into the blue blockers currently available and learn how to make your own.

A Survey of the Blue-Blocker Landscape

Given the bevy of research showing the harmful effects of artificial light — in particular, violet and blue — it makes sense the companies and entrepreneurs have populated the market with blue-blocking glasses.

The table below is by no means an all-encompassing list, but it does represent some of the more popular blue-blocking options available. You’ll note that the BPI options are tints only. I included them as they’re part of the how-to portion of this article.

You could divide this table into two types of blue blockers, i.e., daytime glasses (such as BluTech and Gunnar Optiks) that block portions of the violet and blue light spectrum vs. nighttime glasses (such as Uvex and BPI Monochrome) that block all of the violet and blue spectrum, and either none, some or all portions of the green, yellow and orange spectrum.

Per the introductory science section above, it’s worthwhile to block artificial violet and blue light at all times. Bare minimum, you should block the 380–450 nm range (violet) during the day and the 380–495 nm range (violet and blue) during the night. If you want maximum melatonin production at night, take it a step further and block green (495–570 nm), too.