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Using a screen as a night light without wrecking your sleep

· 9 min read · The WhiteScreen.tv team

A single candle flame glowing warm orange against a dark background
Candlelight, from our screensaver collection. Dim and warm is the right direction for evening light.

This article summarizes published research on light and sleep. It is not medical advice. If you sleep badly for weeks at a time, talk to a doctor.

A phone or tablet makes a handy night light. It is already by the bed, it can show any color, and it can be dimmed. But light in the evening is not neutral. It tells your body clock what time it is, and a bright white screen sends the wrong message.

The short version: at night, make the screen dim, warm or red, below eye level, and off when you sleep. Here is why, and how to set it up.

What evening light does

Your eyes contain a small set of light-sensitive cells that do not help you see. They report brightness to the brain's master clock, and they use a pigment called melanopsin, which is most sensitive to blue light at around 480 nm (Lucas et al., 2014). One of the things this system controls is melatonin, the hormone that rises in the evening as your body prepares for sleep.

Light in the hours before bed holds that signal back:

  • In a study of 116 young adults, ordinary room light (under 200 lux) in the eight hours before bedtime, compared with dim light (under 3 lux), produced a later melatonin onset in 99.0% of participants and shortened melatonin duration by about 90 minutes (Gooley et al., 2011).
  • People differ a lot. In a 2019 study of 55 people, the evening light level that suppressed melatonin by half was about 25 lux for the group, but ranged from 6 lux in the most sensitive person to 350 lux in the least sensitive (Phillips et al., 2019).

Screens have been tested directly. When 12 adults read on a light-emitting tablet for about four hours before bed on five evenings, compared with a printed book, they took about 10 minutes longer to fall asleep, their melatonin onset came about an hour and a half later, and they felt sleepier the next morning (Chang et al., 2015). An earlier study found that five hours in front of an LED-backlit computer screen in the evening suppressed the evening rise in melatonin more than a screen giving off less blue light (Cajochen et al., 2011).

These are small laboratory studies with long exposures, and they say more about hours of reading than about a few minutes of night light. They do show the direction of the effect.

How much light is too much

Light for the body clock is measured in melanopic EDI (equivalent daylight illuminance), a unit defined by the International Commission on Illumination in its CIE S 026 standard (CIE). In plain terms, it is the amount of ordinary daylight that would have the same effect on melanopsin as the light you are looking at. Blue-rich white light scores high; warm and red light score low for the same visible brightness.

In 2022, a group of 18 researchers published consensus recommendations for healthy adults (Brown et al., 2022), measured at eye level:

TimeRecommendation
Daytimeat least 250 melanopic EDI lux
Evening, from at least 3 hours before bedat most 10 melanopic EDI lux
Sleepat most 1 melanopic EDI lux; "as dark as possible"
Night, if you need to seeat most 10 melanopic EDI lux

How does a screen compare? In one set of measurements, a smartphone showing full-screen white at maximum brightness, held 15 cm from the eye, gave 64.3 melanopic EDI lux (Schlangen and Price, 2021). That is more than six times the evening limit, from a single phone.

Why dim and warm both matter

Color. Researchers compare light sources with a ratio called the melanopic daylight efficacy ratio. Daylight is 1 by definition. Brown and colleagues report 0.83 for a 6,500 K white LED and below 0.35 for many warm-white household LEDs of 2,700 to 3,000 K, which is why they say warm white LEDs can light a room in the evening while staying within the limit (Brown et al., 2022). Red light is lower still. By our own calculation using the CIE melanopic sensitivity curve, deep red light around 630 nm affects melanopsin less than 1% as much as daylight of the same visible brightness. A screen set to pure red uses only its red sub-pixels, which is why a dim red screen is the gentlest choice.

Brightness. Color alone is not enough. Brown and colleagues note that changing the color of displays gives only a "modest (approximately 50% decrease)" in melanopic light, and works best "combined with ... dimming of screens and low melanopic ambient lighting" (Brown et al., 2022). A field study backs this up: 167 young adults used their iPhones in bed with Night Shift on, Night Shift off, or no phone at all, and the researchers found "no differences in sleep outcomes attributable to Night Shift" (Duraccio et al., 2021).

So turn the color warm and the brightness down. Distance helps too: light from a screen falls off quickly as you move away from it, which we show with numbers in our video call lighting guide.

Settings on WhiteScreen.tv

Every color screen page has four quick presets. Two of them are for light:

  • Night Light shows a dark red (#4d0f0f) at 45% brightness. By our calculation, that is less than 1% of the visible light the same screen gives on full white, and most of it comes from the red sub-pixels. Even scaled from the phone measurement above, that is well under 1 melanopic EDI lux. Use this one at night.
  • Reading Light shows a warm-tinted white (#fbf0d9) at 85% brightness. It is a pleasant light for reading in the day or early evening, but it is still a fairly bright, fairly white light. It is not a bedtime setting unless you also turn the device brightness right down.

You can also use the red screen or the orange screen directly. On a computer, scroll the mouse wheel in full screen to lower the brightness in 5% steps. On a phone or tablet, use the device's own brightness control, set as low as it goes. That control dims the backlight itself, which our page cannot do.

A few more habits help:

  • Keep it low and pointed away. Put the device below eye level, facing the wall, a book or the floor, not your face.
  • Use night mode as well. Night Shift on a Mac "shifts the colors in your display to the warmer end of the spectrum" (Apple Support), and iPhones, Android phones and Windows PCs have similar settings. On its own it is not enough, but combined with low brightness it helps.
  • Switch it off to sleep. The recommendation for the sleep environment is no more than 1 melanopic EDI lux. Do not tick Keep screen awake for an all-night light. LCD screens also leak some backlight even when showing dark colors.
  • Mornings are the other half. Bright light during the day, ideally outdoors, is part of the same advice. Our article on screens and light therapy explains why a screen cannot replace daylight.

What we do not know

The research has real limits, and it is worth being honest about them:

  • Most studies are small, run in laboratories, and recruit healthy young adults. The 2022 recommendations are explicitly for healthy adults.
  • Exposures in studies are long, often hours. Few studies look at a few minutes of dim light during the night, such as checking on a baby or walking to the bathroom.
  • Sensitivity varies widely between people, by more than 50-fold in the 2019 study above, so the same light can matter for one person and not another.
  • Melatonin timing and sleep are not the same thing. In the tablet study above, melatonin onset moved by about 90 minutes, while the time taken to fall asleep grew by about 10 minutes.

None of this suggests that a dim red screen at night is harmful. It suggests that a bright white one, especially held close to your face for a long time in the evening, is the setup to avoid.

Sources

More from WhiteScreen.tv: the screensaver collection and the changelog. How we source and check articles: editorial standards.