The physiology behind "no screens before bed" advice is well established: light in the blue wavelength range, roughly 450–500 nanometers, suppresses melatonin production more than other colors of light, delays your circadian phase, and prolongs how long it takes to fall asleep.

More recent research adds useful nuance. A 2023 study in Brain Communications compared young men reading on a phone versus a physical book before bed and found that while blue light did suppress melatonin, the negative effect on sleep was largely avoided if the phone was put away at least an hour before lights-out.

The practical takeaway sits between the two extremes: blue-light-blocking glasses and night-mode filters aren't magic, but they're not nothing either. The bigger lever is probably the hour-before-bed buffer — putting the phone down, dimming the room, and doing something that isn't actively stimulating.

Further reading: Blue light has a dark side (Harvard Health).