Everybody wants better sleep, but getting better sleep is hard.
I was trading New Year’s resolutions with a circle of friends a few weeks ago, and someone mentioned a big one: sleeping better. I’m a visual neuroscientist by training, so whenever the topic pops up it inevitably leads to talking about the dreaded blue light from monitors, blue light filters, and whether they do anything. My short answer is no, blue light filters don’t work, but there are many more useful things that someone can do to control their light intake to improve their sleep—and minimize jet lag when they’re travelling.
My longer answer is usually a half-hour rant about why they don’t work, covering everything from a tiny nucleus of cells above the optic chiasm, to people living in caves without direct access to sunlight, to neuropeptides, the different cones, how monitors work, gamma curves, what I learned running ismy.blue, corn bulbs, melatonin, finally sharing my Apple Watch & WHOOP stats. What follows is slightly more than you needed to know about blue light filters and more effective ways to control your circadian rhythm. Spoiler: the real lever is total luminance, not color.
The premise
Right above the optic chiasm lies a nucleus called the suprachiasmatic nucleus (SCN). This is where the brain’s master circadian clock lives. There are a lot of phenomena in the body, whether alertness, body temperature, or hunger, that are at least partially dependent on our body’s sense of time. There’s a set of neurons that are part of the hypothalamus that autonomously track time, by a fascinating set of transcription-translation feedback loops involving proteins that ultimately shut down their own translation in a cycle that lasts about 24 hours. The cells in the SCN also synchronize with each other through neuropeptides, and diffuse the master clock signal throughout the body; melatonin from the pineal gland, but also via secondary regulation of the HPA (stress axis), and a neuropeptide called AVP.
The intrinsic clock is not very precise, with a cycle that typically lasts a little more than 24 hours, something which was first verified in people living deep underground in abandoned mines (for science!). One factor that ultimately resets the clock is input from a set of neurons inside the retina that project to this nucleus. Those cells are called intrinsically photosensitive retinal ganglion cells (ipRGCs). Breaking this down:
A retinal ganglion cell is a cell in the retina (the back of the eye) that ultimately projects to the brain
Intrinsically photosensitive means these cells don’t rely on signals from cones or rods to get light information; the cells directly express a light-sensing molecule, an opsin, called melanopsin.
ipRGCs are not image-forming, and they don’t project to visual cortex; they’re just there to track ambient light, relaying information to the SCN. Crucially, melanopsin is often said to be sensitive to blue. Therein lies the premise of blue light filters: if you cut the blue out of your display at night, you will help your body’s clock synchronize, and fall asleep more easily; or at the very least, it will stop your brain’s internal clock from getting delayed.
A flawed premise
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