Recently my brother mentioned that he was sleeping better since he got new prescription glasses with a blue light filter. He wears his glasses primarily to read screens (both computer and smartphone) during the day at work. So I was intrigued, but a little skeptical: could daytime use of blue light filtering glasses make a difference in the quality of my sleep? How, when and why blue light affects us seemed like good questions to ask an expert before deciding if these glasses could help me too.
What is blue light?
Visible light comprises a short segment of wavelengths nestled in the electromagnetic radiation spectrum. Together, the wavelengths of visible light picked up by our eyes are translated into white light by our brain.
You may remember looking through a prism to bend the wavelengths that make up white light into a rainbow of colors. At one end of this rainbow, the blue light turns purple. Sunlight has a lot of light at all visible wavelengths.
Measured in nanometers (nm), visible light wavelengths range from 400 to 700 nm. The wavelengths of blue light are between approximately 450 and 495 nm. And different slices of blue light wavelengths have different effects on our bodies, including sleep and alertness.
How does light affect our body?
In addition to helping us see, light also has non-visual effects on the body, says Dr. Steven Lockley, a neuroscientist in the Division of Sleep and Circadian Disorders at Harvard-affiliated Brigham and Women’s Hospital.
The 24 hour circadian clock in the brain regulates sleep and wake cycles, hormonal activity, diet and digestion, as well as other important processes in the body. “Special photoreceptors in the eye detect light to control our circadian rhythms,” he says. These cells contain a non-visual photopigment called melanopsin, which is most sensitive to 480nm light at the blue-green end of the visible light spectrum. Other visual photoreceptors called cones allow us to see even shorter wavelengths of blue-violet light at around 450 nm.
How can blue light affect sleep?
During the day, blue enriched light is desirable because it helps synchronize our circadian clocks over a 24-hour day. So, exposure to a regular cycle of light and dark is essential for getting and maintaining good sleep.
Stimulating certain wavelengths of blue light helps us stay alert, whether it comes from a natural source like the sun during the day or from electronic devices that emit blue light. While stimulation is useful during the day, at night it can interfere with sleep. Exposure to blue light at night – for example, watching a TV series on your laptop just before bed – will stimulate cells containing melanopsin and alert the brain, making it think it is daylight. This can make it harder to fall asleep and can affect the quality of your sleep.
Blue light filtering: can it help a tired body and tired eyes?
Although a recent systematic review suggested that blue light-blocking glasses may help people with insomnia, Dr Lockley says there aren’t enough study details to draw this conclusion. Most commercially available blue light filtering lenses and special coatings added to prescription lenses are not standardized. So you have no way of knowing which wavelengths are blocked and whether it affects only visual function or important non-visual functions such as alertness and the circadian clock. In addition, the timing, duration and nature of nighttime light exposure in the summary of these studies was unclear.
If you want to block out stimulating blue light that might interfere with sleep, avoid using a screen after dusk as much as possible, especially within two to three hours of bedtime. You can also try using computer software that reduces the amount of blue light emitted. Examples include Night Shift (available on Apple devices) or f.lux, a free download available for all computers and paired devices. You should also try to resolve other issues that are affecting your sleep.
To help reduce eye strain, a common concern for people who use screens often, the American Academy of Ophthalmology advises taking regular breaks using the 20-20-20 rule. Every 20 minutes, look away from your screen towards an object about 6 meters away for about 20 seconds.
You should also expose yourself to as much daylight as possible between uses of the screen to provide a strong circadian and alerting stimulus, especially if you spend most of your time indoors.
As for my brother, he hardly watches television and tends to prefer reading printed books at night. He agreed he might experience a placebo effect from the blue light filter on his new glasses – or just sleep better now that he has the right prescription, and therefore less eye strain.
As a service to our readers, Harvard Health Publishing provides access to our library of archived content. Please note the date of the last revision or update of all articles. Nothing on this site, regardless of date, should ever be used as a substitute for direct medical advice from your physician or other qualified clinician.