How light controls your sleep
Deep in your eye, beyond the cells you see with, sit special light sensors called intrinsically photosensitive retinal ganglion cells. They contain a pigment called melanopsin and are most sensitive to blue light around 460 to 480 nanometers.
When these sensors detect blue light, they send a direct signal to the master clock in your brain, the suprachiasmatic nucleus. That clock decides when your body releases melatonin, the hormone that starts sleep. Blue light in the evening tells the clock it is still daytime, so melatonin is delayed and you stay alert when you should be winding down.
Not all lenses are the same
Blue light at night and melatonin
In a 2015 study in the Proceedings of the National Academy of Sciences, Chang and colleagues had people read on a light emitting device before bed. Compared with a printed book, it suppressed melatonin, delayed the body clock, made it take longer to fall asleep, and left people less alert the next morning.
Earlier work by Gooley and colleagues in 2011, in the Journal of Clinical Endocrinology and Metabolism, found that ordinary room light before bedtime suppressed melatonin and shortened the window in which the body produced it. Research summarized by Harvard notes that blue light suppresses melatonin for about twice as long as green light and shifts the body clock about twice as much.
What happens when you block it
A 2017 study by Ostrin and colleagues in Ophthalmic and Physiological Optics found that wearing blue blocking glasses in the evening raised night time melatonin. A 2018 randomized trial by Shechter and colleagues in the Journal of Psychiatric Research found that amber blue blocking glasses worn before bed improved sleep in people with insomnia. Earlier, Burkhart and Phelps in 2009 reported better sleep quality and mood when amber lenses were worn in the hours before sleep.
The daytime side matters too. Bright light early in the day strengthens the body clock and is linked to better sleep at night, which is why we pair evening filtering with daytime lighting. The takeaway across this research is simple. Manage the light your eyes receive, and you help your natural rhythm do its job.
