‘Night-mode’ yellow screens might actually keep you awake

Scientists have cast doubt on the theory that the amount of ‘blue light’ given off by computer and phone screens can make it difficult to sleep.

Experts have long thought that blue light suppresses the hormone melatonin, which helps to control our sleep patterns.

But researchers at Manchester University said it’s not the colour that matters, but how bright the screen is. Their work calls into question the effectiveness of ‘night-mode’ settings in apps and software that reduce the amount of blue light before bedtime.

In tests on mice, they used light that could adjust colour without changing brightness. Blue ‘cooler’ colours had a weaker effect on the animals’ body clock than equally bright yellow ‘warmer’ colours.

As a result, the study claims, changing screens to yellow in the evenings actually keeps you awake, and counteracts any benefit of dimming the screen.

Lead researcher Dr Tim Brown said the findings matched what happens in the natural world, where yellow daylight tells us to be alert, while blue twilight signals it’s time to sleep.

“During the daytime, the light that reaches us is relatively white or yellow and has a strong effect on the body clock, and around twilight, once the Sun sets, the bluer the light becomes,” he said.

He added: “So if you want to avoid light having a strong effect on your body clock, dim and blue would be the way to go”.

While mice are nocturnal, Dr Brown said the way light affects the body clock is the same across all mammals, so the research can be applied to humans.

However, some sleep experts urged caution. Dr Manuel Spitschan from Oxford University said: “This is fascinating work but we really don’t know yet that the same happens in humans. That’s the difficulty with animal work”.