May 18, 2019
In sourcing the best sleep-related products on the market for Wink & Rise, we have repeatedly encountered so-called “blue-light blocking” products. This piqued our curiosity about whether such products might work and how, so we explored some of the research surrounding blue light and its effects on sleep. And there is a lot of research related to this topic. We thought Sleep Journal readers might be interested, so we've summarized some of the most relevant science below.
Visible light travels as electromagnetic waves of different lengths. Longer wavelengths carry less energy than shorter ones, which cause us to perceive them differently: we see longer waves as warm colors, like red and orange, and shorter waves as cooler tones, such as blue and green. While the specific definitions vary from study to study, generally “blue light” corresponds to light waves with a length of about 400-490 nanometers (nm).
Because waves in this range transmit more energy per photon, they interact differently with our eyes, and this is where things get interesting. One 2018 study of blue light found that shorter wavelengths penetrated deeper into the tissue of the eye, with wavelengths between 415 and 455 nm being particularly harmful. Studies in humans and rats indicate that blue light is particularly stimulating to non-image-forming retinal ganglion cells in the eye, which are active even in blind individuals. These cells contain melanopsin, a protein that changes shape when exposed to blue light. When this happens, the cells transmit information to the suprachiasmatic nuclei (SCN), two tiny bundles of cells in the brain’s anterior hypothalamus that are responsible for regulating our circadian rhythms.
While we tend to think of the circadian rhythm in terms of a 24-hour day, it actually varies from individual to individual. Like a clock running a bit too slowly or quickly, if left unchecked this variation would gradually add up so that our sleep-wake cycle was out of sync with night and daytime. Harvard researcher Dr. Charles Czeisler’s extensive research has demonstrated that the SCN allow our brains to sync our personal circadian rhythms to the 24 hour light-dark cycle, so that this doesn’t happen.
Early morning and daytime sunlight is rich in blue wavelengths, and by stimulating the SCN it triggers the body to wake up and become more alert. Various studies have found that exposure to blue wavelength-enriched light during the morning and daytime can enhance cognition, reaction times, and mood. Michael J. Breus, popularly known as The Sleep Doctor, cites a study that found that even 30 minutes of blue light exposure in the morning was enough to have a positive effect on reducing daytime sleepiness and improving performance.
Likewise, the lessening of blue wavelengths—and light levels in general—throughout the day into the evening, causes the SCN to trigger the secretion of melatonin from the pineal gland, which lets our bodies know that it’s time to sleep. Investigations of the effect of light intensity and wavelength on melatonin levels suggest that wavelength is more important than intensity in suppressing melatonin production.
One study found that exposure to 460 nm (blue) wavelengths reduced participants' melatonin levels twice as much as exposure to 550 nm (green) wavelengths. Additional studies have revealed that even small amount of blue light can be as powerful at producing these effects as bright “white” (mixed wavelength) light that was 185% more intense, and Harvard researcher Stephen Lockely notes that levels as low as 8 lux, about twice the brightness of a typical nightlight, can produce a notable suppression of melatonin levels.
Such exposure has a profound detrimental effect on sleep. A 2017 study showed that blue light exposure between 9 and 11 pm decreased the time participants slept by an average of 16 minutes and increased the number of times they awakened during the night by approximately 50%. In addition to producing lower levels of melatonin, blue light exposure prevented the natural cooling of core body temperature, another mechanism that triggers sleep onset. In comparison, exposure to red light wavelengths did not affect melatonin, body temperature, or sleep. And according to another study, melatonin suppression by nighttime blue light exposure is as much as twice as severe in children than in adults.
Perhaps you’ve already heard that you should avoid using electronic devices close to bedtime because they can make it harder to fall asleep. One reason for this is that we tend to use such devices for stimulating activities that don’t allow us to relax and unwind in preparation for sleep. But another, stealthier, reason is because of the high levels of blue light that they emit.
Most electronic devices, including computer monitors, tablet and smart phone screens, and e-book readers, are lit by LEDs, which produce light in the 400-490 nm blue range (so-called “white” LEDs are created by combining blue LEDs with yellow phosphors to give the light a warmer perceived tone). A 2011 study showed that controlled evening exposure to an LED-backlit screen resulted in both lower melatonin levels and lower perceived sleepiness, as well as enhanced alertness and cognitive performance. Similarly, a 2015 study of how using an e-reader before bed compared to reading from a printed book found that using an e-reader reduced participants' melatonin levels by an average of 50%, reduced their perceived sleepiness, increased the time it took them to fall asleep, decreased the time they spent the REM stage of deep sleep, and reduced their levels of alertness the following morning.
Such findings are significant, considering that surveys suggest that up to 90% of Americans now use some type of electronic device within an hour of bedtime on a regular basis. Moreover, many such devices are held close to the user’s face, which increases the amount of light exposure exponentially compared to viewing light of similar wavelength and intensity from a greater distance. Unfortunately, while many devices and apps now offer color-temperature shifting modes designed to decrease blue light exposure, at least one study has found such interventions to be ineffective at preventing melatonin suppression.
Well, the first step is to become more mindful of what type of light you are exposing yourself to at different times of the day. In the morning and during the day, bright and blue-enriched light can produce beneficial effects, with one study suggesting that morning exposure can actually offset the circadian disruption caused by evening exposure and another recommending further research into its therapeutic potential.
The next step is to try to limit your exposure to blue light in the evening and at night. Color-shifting smart lightbulbs are one way to control this in your immediate environment, as is limiting the amount of time you spend using electronic devices in the evening. However, if not using your device is not practical, several studies have shown that filtering out a narrow range of short wavelength light is effective in reducing or preventing the suppression of melatonin secretion and the sleep disruptions that result from this. Because such filters only block a narrow portion of the visible light spectrum, they can reduce the circadian-shifting effects of blue light without producing a noticeable difference in color perception.
There are numerous types of blue light-blocking glasses on the market, including some that absorb short wavelengths and some that reflect them, as well as blue-blocking screen protectors for electronic devices. Some of our favorites are EyeJust’s iPhone and iPad screen protectors, which have been validated to block up to 50% of 440 nm to 460 nm light emissions by a study at the University of California-Irvine.
We hope this post has helped you understand the mechanisms by which exposure to different types of light can affect your sleep, performance, and health, and made it easier for you to take proactive steps in seeking out the right types of light at the right times of day. As always, thank you for reading, and sleep well.
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