Chris Lakin

How blocking blue light affects sleep.

Note: this is a bit of an old article and not my best work. I will update this eventually.

Block light is almost completely blocked

I wear blue-light blocking glasses every night. Here's why—

The Study

Attenuation of short wavelengths alters sleep and the ipRGC pupil response


The Experiment

21 subjects (aged 17-42) were asked to wear glasses that block 99% of blue light. The glasses were worn for at least 3 hours before sleep for two weeks. Melatonin (a sleep hormone that peaks during sleep) was measured (via saliva) before and after the experiment.


Results

At the beginning of the experiment, melatonin was measured to be 16.1 pg/mL on average between the subjects. Melatonin was measured at night.

After two weeks, the average was 25.5 pg/mL, a 58% increase. P-value of less than 1%!

Difference in melatonin levels (via saliva) before and after two weeks of using blue-light blocking glasses at night

Additionally, sleep duration increased by 24 minutes. P-value less than 0.1%.


Possible Confounding Factors

Brightness

Both this research and my opinions may be focused too much on the 'blue' part of this. It may be possible, for example, that the overall brightness-reducing effect of the glasses is more significant than the blue light-reducing effect. The study above compares wearing blue-blocking glasses to a control of not wearing the glasses. I am not aware of a study that compares blue-blocking glasses to sunglasses, for example. This also opens the door for a placebo effect.

A 2014 study comparing the effects of e-reading and paper reading on sleep was also unable to discern whether the e-reading affected sleep by blue light, or just brightness.

When was night melatonin/saliva measured?

Subjects were instructed to sample their own saliva just before their normal bedtime. This is discussed further under "Melatonin analysis" in the paper.

Saliva Measurements

Do saliva measurements of melatonin reliably predict melatonin levels within the body?


Get Your Own

I wear these glasses every night. They are made by the same brand as the glasses that were used by the study. (The brand was not affiliated with the study.)

If you would like to get a pair for yourself, this is what I use. (Amazon affiliate link: As an Amazon Associate I earn from qualifying purchases.)

I've been wearing these exact glasses since 2017, and in my experience they last at least a year. (Also, these glasses do have adjustable angle and length. The lens also pops out for easy cleaning. This took me a year to figure out.)

Note that other "blue light-blocking" glasses say they block blue light, but fail to say how much. I do not know of any effective glasses (blocks 80%+) that are not bright orange.

One more note: while some other blue-blocking glasses may have good lenses that block a meaningful amount of blue light, I'm not sure how much that matters if the glasses don't wrap around your eyes. Especially if the glasses still allow you to see blue from the brightest part of a room (the ceiling).


Other Research

This is not an exhaustive review. I have only briefly reviewed other papers investigating this question. I have heard of in vitro evidence against "less blue light → better sleep", but I am yet to see any in vivo counter-evidence.

This is another study to consider. It draws the same conclusion as the study above. There's a nice graph on page 5 comparing teenage males that wore the glasses with those that didn't. I haven't had the time to review this other paper deeply, though.

Having trouble accessing the paper? Use SciHub.

[More papers via Google Scholar search]


Other Notes

This is also why I set my light bulbs to go red (and dim) after ~6:30pm.


2020 July (posted) - 2020 September (updated)