When Do You Need Protective Eyewear for a Good Night’s Sleep?

Elizabeth Saenger, PhD

In the old days, Mother Nature turned off the lights at bedtime. Now we have artificial light 24/7, and its unintended consequences.

To figure out whether, and when, you need protective eyewear, you need to know about the kind of light that can disrupt your sleep, or harm your eyes. And you need to know that the kind of light you might see for up to three hours before you go to bed can keep you up at night.

In other words, getting ready for bed really means getting your eyes ready for bed about two to three hours before your head touches the pillow. Before the advent of candles, and electricity, such advanced planning was not necessary because Mother Nature turned off the light at sunset.

What kind of light disrupts sleep?

What kind of light disrupts sleep?
Newton (1643-1727) did a series of studies to discover that although white light appears white, it is really a combination of light of different colors.

Blue light is part of the spectrum of white light, as the English genius Isaac Newton discovered when he shone white light through a prism. As scientists discovered centuries later, it is this part of the spectrum that has special effects on our nervous system.

First, when blue light hits cells in the retina–cells not related to vision, but to regulating our circadian rhythms, or internal clock–it tells our bodies that it is daytime. This message energizes us, which is fine when we want to listen to a lecture, or play tennis, but not convenient if we are trying to relax.

Second, exposure to blue light in the evening, or during the night, tells our body that it is still time to be awake, and pushes our body’s perception of bedtime into the future. That’s because white light (and the blue light within it) stimulate the melanopsin in our retina (not to be confused with the sleep hormone, melatonin, produced in our brains). When melanopsin is stimulated, it is likely to keep you up.

For the same reason, exposure to night lights with white light make it harder to go back to sleep if you get up in the middle of the night.

Third, blue light at night can harm the eyes. At the risk of oversimplifying the mechanisms involved in sleep, the hormone melatonin, released daily by the pineal gland, is most abundant at night. Melatonin’s presence in the retina makes us more sensitive to blue light. As a result, at night we are most attuned–and vulnerable–to blue light.

Protective eyewear

melanopsin
The melanopsin in the retina is most sensitive to blue light at 480 nm. However, the protein melanopsin (not to be confused with the hormone melatonin) reacts to a range of light around that frequency.

Amber glasses may allow you to work under bright white lights without a problem if the glasses filter out exactly the right part of the spectrum. Specifically, the glasses need to filter out blue light with a wavelength (frequency) of 480 nanometers, and part of the visible spectrum with frequencies both above and below that point.

If this light is not filtered out, it will fool certain cells in the retina into responding as if it is day. These cells cannot tell the difference between light from the sun, and artificial light. Thus, when certain wavelengths of blue light strike them, they will tell the body’s inner clock that it is day, and your body should stay awake. This means you will not start producing melatonin in preparation for sleep.

There are many inexpensive amber, orange, and yellow glasses, advertised as “blue blockers,” which filter out some, but not all, of the light in that critical range. Specifically, they do not block some of the green light which affects circadian rhythms. As a result, they do not work as well as glasses that cover the complete range of melanopsin sensitivity.

This construction worker wears high-quality protective eyewear. The right wavelengths of light are blocked, and the sides of the glasses prevent light, as well as construction dust, from leaking into his eyes from the sides.

To be effective, amber glasses also need to block light from coming in from the sides of the glasses, near the temple. Some protective eyewear, like the curated collection here, blocks out exactly the right range of light, protects the eyes from light near the temples, and, according to some wearers, looks cool!