1. The 480nm Problem: Why LED Light Matters at Night#
For most of human history, after sunset the only light came from fire, embers and candle flame. These sources give mostly warm, long-wavelength light with very little blue.
White LEDs changed that.
Modern LED screens and energy-efficient bulbs make "white" light with a gallium nitride (GaN) blue diode coated with a yellow phosphor. The result is a strong blue peak around 450 nm, close to the range that melanopsin in your retina's ipRGC cells responds to most (around 480 nm).
Screen light is hundreds of times dimmer than daylight, but at night your clock is at its most sensitive, so even modest light can delay melatonin.
2. How Much Light Suppresses Melatonin#
Melatonin doesn't put you to sleep directly; it tells your body that the day has ended. Many people assume you need blinding light to suppress it. Lab studies show otherwise:
- In one study, ordinary room light of about 25 lux was enough to cut melatonin by half in the average person, with big differences between people (Phillips et al., 2019, PNAS).
- A phone held close to your face at full brightness can deliver tens of lux to your eyes.
- In another study, reading on a light-emitting e-reader for about four hours before bed on five nights delayed melatonin by about 1.5 hours compared with a printed book, and left people less alert the next morning (Chang et al., 2015, PNAS).
3. Software Filters (Night Shift) vs Optical Lenses#
Can you simply turn on Apple Night Shift or f.lux and keep scrolling in bed?
The Truth About Software Night Modes:
Software filters shift screen color from cool blue to a warmer amber tint. This cuts some blue light, but not all of it. If the screen stays bright, the total amount of light still matters, so turning brightness right down does more than the colour shift.
Other Options:
- Amber Glasses: Amber blue-blocking glasses may help some people in the evening at home, but the evidence is mixed; dimming your lights does more. Never wear them for driving.
- Red Screen Tint: On iOS, go to Settings > Accessibility > Display & Text Size > Color Filters and choose a red Color Tint, then add it to the Accessibility Shortcut (triple-click) to toggle it quickly. Melanopsin responds very weakly to red light.
4. A Darker Evening and Bedroom#
- 1.Dim Overhead Lights About 2 Hours Before Bed: Switch to low-wattage, warm bulbs in lamps placed below eye level.
- 2.Dark Bedroom: Make the room as dark as you can, or use an eye mask. In one study, sleeping with a bright (100-lux) overhead light on raised night-time heart rate and next-morning insulin resistance (Mason et al., 2022, PNAS).
- 3.Cover Standby LEDs: Put a small piece of tape over bright standby LEDs on chargers and power strips (never tape over or cover a smoke alarm).
5. A 60-Minute Screen-Free Wind-Down#
60 minutes before target sleep onset:
- Power down laptops, tablets, and mobile devices.
- Choose low-effort, hands-on activities: a paper book, journaling, foam rolling, or conversation.
- Give your body time to shift out of "on" mode before you turn the light off.
ARC can send a wind-down reminder timed to your bedtime, so the screens-off hour starts without you tracking it. The other half is morning: brighter days appear to make you less sensitive to evening light, and ARC's 20-minute morning-light timer handles that (see the morning sunlight guide).
For a fuller evening routine, see the evening wind-down ritual, and for what melatonin does beyond sleep, melatonin: more than a sleep hormone.
Educational content, not medical advice. ARC is a wellness app, not a medical device. If sleep problems persist, talk to a doctor.