Blue Blocking Glasses Can Prevent Circadian Disruption Without Changing the Time You Fall Asleep

Why sleep onset is such an insensitive measure of circadian health

For the first 10,000 generations of human existence, we never had to worry about exposure to blue light in the evenings. Wood fires and candles contained virtually no blue, and nights were dark. But in the last ten years, we have entered the era of ubiquitous blue-rich LEDs in our screens and lights. This is less of an issue during the day, especially if you get regular exposure to natural daylight, but creates significant health problems in the evening and at night.

One obvious solution has been to use blue-blocking glasses in the evening, especially if you cannot change the lights and screens you use. A recent market research report tells us that it has already grown into a $2.7 Billion global market and is projected to grow to $5.2 Billion by 2032.¹

But there are two major problems which risk undermining the scientific credibility of blue-blocking glasses:

1. Many blue-blocking glasses block the wrong blue.

2. Even glasses that block the correct circadian-sensitive blue wavelengths may have only a minor effect on the time you fall asleep.

Before you are tempted to throw away your blue-blocking glasses, you should know there is a major health benefit to using the correct blue-blocking glasses in the evening. As I explain below, they prevent the circadian clock disruption that underlies many of the chronic diseases of our modern era.

Blocking the Correct Blue

Many of the best-selling blue-light-blocking glasses block the wrong part of the blue light spectrum. There are many different color wavelengths in the 420 - 500 nm blue light range, and they have quite different biological effects. 420 nm violet blue stimulates alertness, 440 nm indigo blue can damage the eyes but only at very bright outdoor sunlight intensities, 460 nm royal blue can cure jaundice in newborns, and 480 nm sky blue is the most effective daytime synchronizer for circadian clocks, but will disrupt our clocks and health at night.

Glasses with a slight violet-blue tint are ineffective because they do not block the blue wavelengths that disrupt circadian rhythms in the evening. Eyewear that is effective has a yellow-orange color.

Some of the biggest-selling “blue blocker” eyewear filter out blue light mostly below 450 nm. But the peak circadian blue effect is at 480 nm which these clear-looking glasses barely touch. The giveaway for placebo glasses is that are only lightly tinted to make them look attractive. In contrast, glasses that remove the most circadian active blue wavelengths (between 440-495nm) are distinctly yellow-orange in color.

It’s Not About the Time You Fall Asleep

Some sleep scientists have recently suggested that evening blue light is not an issue because it has minimal effects on the time you fall asleep.

However, the timing of sleep onset is not simply determined by your master circadian clock. There are at least three other major factors:

The first is homeostatic sleep drive - the pressure to sleep that is determined by the number of consecutive hours you have been awake. The longer you stay continuously awake, the greater the pressure to sleep.

The second is your level of arousal. Chemical stimulants like caffeine can delay the time that you are able to fall asleep. So can other types of arousal, such as an argument with your partner or spouse, watching a horror movie, or receiving a disturbing phone call or text. Conversely other substances can make you sleepy and advance the time of sleep onset.

The third is our conscious ability to fight off sleepiness for a while if we have something important to do. That can be risky if you are driving a car or in some other hazardous situation because sleep pressure can override your conscious ability to stay awake.

So sleep onset is not simply determined by the time on your circadian clock.

Evening Blue Light Exposure Causes Something More Insidious

In studies of people living their regular lives during the day and sleeping at night, exposure to blue light in the evening makes less than 10 minutes difference in the time they fall asleep.

For example, when young men and women in their 20s read an e-book on a blue-rich screen for four hours before bedtime, for five consecutive nights, sleep onset was only delayed by 9 minutes as compared to when they read a print book in a dimly lit room².

Did that mean blue light exposure in the evening was not a big deal? No, it was quite the opposite, and far more insidious.

The blue light exposure in the e-book readers suppressed their melatonin levels and caused a 90-minute shift in the timing of their master circadian clock. The blue light also suppressed REM (dreaming) sleep, and the e-book readers were much sleepier the following morning and they took several more hours before they fully felt awake as compared to the week when they read a print book in the evening.

In another study, high school students wearing blue blocking glasses in the evening for a month, and using a light box in the morning, showed little change in the timing of sleep onset³ . However, their daytime attentiveness was substantially improved, and they scored better on math tests. Furthermore, MRI scans showed that the size of the dentate gyrus was increased, a part of the brain that plays a critical role in memory formation and retrieval, and brain connectivity circuits were enhanced.

The Danger of the Effects You Cannot See

We tend to use the timing of our sleep - the time we fall asleep and when we awake as a yardstick of our health, because it is something that we are so well aware of. However, sleep onset is a relatively insensitive measure of circadian health, and there are much more sensitive measures of our health that are not so readily apparent.

Blue light in the evening both suppresses the natural rise in melatonin and causes circadian disruption which may occur with little effect on when you fall asleep. Sleep onset may have only shifted by 9 minutes, but the timing of the circadian clock was delayed by 90 minutes in the study of blue-rich e-book readers, creating an internal circadian disruption.

This is important because the causal pathway of the wide range of disorders caused by blue-rich light at night involves melatonin suppression and circadian disruption, where the rhythms in various body functions are out of sync with each other. This is a key contributor to the modern epidemic of obesity, diabetes, heart disease, psychiatric depressive disorders, and endocrine-sensitive cancers such as breast and prostate that are exacerbated by blue-rich light at night.

The Bottom Line

Protecting your eyes from blue light exposure in the evening is vital for your health. You can do this with blue-blocking glasses that exclude all 440-495 nm blue light. Or you can use light bulbs and fixtures that provide light with less than 2% sky blue content at night.

Even if you fall asleep at the usual time, you can be assured that you are protecting your circadian health.

Sources

For further details, please consult my new book, THE LIGHT DOCTOR: Using Light to Boost Health, Improve Sleep, and Live Longer.

Buy a copy THE LIGHT DOCTOR and share copies with your friends and colleagues.

Give the book to people who need to hear and know about healthy lighting. It is the essential guide to healthy lighting.

Disclosure

In the interests of full disclosure, I hold a minority equity interest in Circadian Eye LLC which sells circadian blue-blocking eyewear under the brand BlueSafe24. I also have a minority equity interest in Korrus which sell zero blue light bulbs and light fixtures. In addition I receive royalties on sales of my book THE LIGHT DOCTOR.

1. Acumen (October 2024) Blue Light Blocking Glasses Market Size - Global Industry, Share, Analysis, Trends and Forecast 2024 - 2032. https://www.acumenresearchandconsulting.com/blue-light-blocking-glasses-market Archived November 30, 2024 at https://perma.cc/5E4S-95F3

2. Chang A-M et al (2015) Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness. PNAS 112: 1232–1237 https://www.pnas.org/doi/pdf/10.1073/pnas.1418490112

3. Teicher MH, et al. (2023) Bright light therapy and early morning attention, mathematical performance, electroencephalography and brain connectivity inadolescents with morning sleepiness. PLoS ONE18(8): e0273269. https://doi.org/10.1371/journal.pone.0273269