Blue light and melatonin: what does your screen do to your evening?

What is melatonin, and why does the body care about light?

Melatonin is the hormone the pineal gland in your brain starts releasing when it gets dark. It is the body's chemical message that night has begun. It does not knock you out like a pill, but it starts the processes that make you sleepy, lower your core temperature and switch the rest of the system towards rest.

Darkness is detected by a separate type of cell in the retina, not the rods and cones you see with. These cells contain a light-sensitive protein, melanopsin, and send their signal straight to the brain's internal clock. In 2001, researchers at Thomas Jefferson University tested 72 people with single wavelengths across 627 sessions. Wavelengths between 446 and 477 nm, which is blue light, were the most effective at switching melatonin off.

How much light does it take to suppress melatonin?

Less than most people think. A 2019 study in PNAS measured how much evening light it takes to halve melatonin. At group level, under 30 lux was enough, roughly what a floor lamp or a bright phone screen gives off. 10, 30 and 50 lux delayed melatonin onset by 22, 77 and 109 minutes respectively.

The same study found huge differences between people: more than 50-fold between the most and least sensitive participant. Two people in the same living room can get a completely different signal from the same lamp.

Another study of 116 healthy 18 to 30-year-olds compared ordinary room light with dim light in the eight hours before bed. Under room light, melatonin started later in 99% of participants, and the window during which the body produced melatonin shrank by about 90 minutes. The body's sense of how long the night is gets shorter, not just the time it takes to fall asleep.

Is it the screen or the lamp?

Both. A screen sits close to your eyes, gets used for hours and is rich in blue. That is why the Harvard e-reader trial showed such a clear effect. But the ceiling light, the kitchen spots and the TV feed the same signal.

There is a difference people rarely mention. Your phone's night mode changes the colour of one light source. A lens in front of your eyes filters all the light that reaches the retina, whether it comes from the screen, the lamp or the TV. That is why glasses and night mode are not the same thing.

What does an orange or red lens do to the signal?

A lens does not remove light in general. It removes certain wavelengths. What makes it relevant for the evening is whether it covers the 446 to 477 nm band, and ideally a bit more. Melatonin sensitivity falls off towards green but does not disappear: in another study by the same group that year, 505 nm was about four times more effective than 555 nm.

The red lens is built to reach past the blue and take in the green part of the spectrum. The orange lens covers the blue band but lets more light through, so you see colours better in the early evening. LOWLIGHT ONE is a day lens and is not made for the evening.

What do studies with actual glasses show?

Three studies are worth knowing. In 2006, Canadian researchers sat 14 people in bright light in the middle of the night wearing orange glasses or grey control glasses. The orange glasses kept the light from suppressing melatonin. In 2015, 13 teenage boys wore orange or clear glasses in front of LED screens for a week. With orange glasses, the screen's effect on melatonin was dampened and they felt sleepier before bed. In 2018, 14 adults with insomnia symptoms wore amber or clear glasses for two hours before bed over seven evenings. With amber they reported better sleep, and wrist trackers recorded longer total sleep time.

What has not been shown matters just as much. The 2023 Cochrane review judged the evidence on sleep in adults too weak to say whether blue light glasses make a difference. Most lenses in that review were ordinary clear blue light lenses. So we do not promise better sleep. We publish what the lens filters, in which band, and what research says about that band.

How do you use them so it counts?

In 2022, a group of 18 light and sleep researchers published recommendations for indoor light. The core is three numbers: at least 250 lux of melanopic light during the day, no more than 10 in the last three hours before sleep, and no more than 1 in the bedroom. A lens solves only one of those. Here is where it fits:

• Get daylight in the morning. How sensitive you are in the evening depends partly on how much light you got during the day.
• Put the orange lens on at sunset, or when you sit down at a screen after dinner.
• Switch to red for the last two hours and keep them on until the light is off, bathroom included.
• Turn screen brightness down and use lower lamps. The lens works best on top of less light, not instead of it.

For the whole evening as a checklist, see The Evening Routine, seven steps with sources. If you are unsure which colour fits when, read Yellow, orange or red lens.