Screens before bed — it's the brightness, not just the blue

Dim the room and turn your screen brightness down for the hour before bed. Don’t rely on a blue-light filter or a pair of amber glasses to do the job on its own — the research on those specifically is weaker than the marketing suggests.

Why this works

Light in the blue part of the spectrum, roughly 460–480 nanometres, is what a specific set of receptors in the eye responds to most strongly, and those receptors feed directly into the part of the brain that controls your circadian clock and melatonin release. Lab studies confirm this clearly: sit under blue light in the evening and melatonin stays suppressed for hours, while the same duration of red light lets it recover within about an hour. So the mechanism behind “blue light delays sleep” is real and well established.

Where the popular advice goes wrong is in the proposed fix. A 2025 meta-analysis pooling randomized trials of blue-light-blocking glasses found only a small, statistically unconvincing effect on actual sleep outcomes measured with wrist trackers — not nothing, but nowhere near what the mechanism alone would predict. The likely explanation is that total brightness matters as much as colour. Research on device use before bed finds that sleep onset gets delayed at screen brightness levels as low as 30 lux, regardless of how much blue is filtered out. A dim, blue-filtered screen at close range can still be delivering more light to the eye than a well-lit, unfiltered room from a distance.

That reframes the useful action: it’s not really “avoid blue light,” it’s “reduce overall light exposure and give the room a chance to look like evening” — which blue-light glasses only partially achieve, while dimming everything does more directly.

How to do it

1. Lower screen brightness manually in the evening rather than trusting a “night mode” colour shift alone to do the work — the colour shift helps a little, the dimming helps more.
2. Dim the room’s overall lighting an hour before bed. Lamp-level light, not ceiling light.
3. If you use blue-light glasses already and they seem to help, keep using them — a small effect isn’t zero. Just don’t treat them as licence to keep every other light at full brightness.
4. Hold the phone or screen further from your face where practical — light exposure to the eye drops off quickly with distance.
5. If total screen avoidance before bed isn’t realistic, this is the more achievable middle ground: dim, distant, brief, rather than bright, close, and open-ended.

Common mistakes

• Buying blue-light glasses and considering the problem solved. The trial evidence for the glasses alone is weak; they’re a small addition to dimming, not a substitute for it.
• Trusting “night mode” without also lowering brightness. Warmer colour with the screen still at full brightness keeps a meaningful amount of light reaching the eye.
• Fixing the screen while leaving the room fully lit. Overhead lighting at full brightness undermines the point of a dimmed screen.
• Treating this as an all-or-nothing rule. A bright room and a screen right before bed on one night isn’t a disaster; it’s the routine average across most nights that matters for the clock.

What should change

On nights you dim both the room and the screen in the hour before bed, expect somewhat easier sleep onset within days, more clearly on nights you’d otherwise have been on a bright screen close to bedtime. This is a smaller, more marginal effect than the big-ticket items — fixed wake time, morning light, caffeine timing — so don’t expect it to fix insomnia on its own if those aren’t already in place.

Your next step

If you’ve dimmed the evening and sleep onset still isn’t improving, the bigger levers are almost always wake time consistency and caffeine timing — check those before assuming light is the remaining problem.