Impact of light from devices on sleep may be overstated, scientists say

Light exposure sets our circadian rhythm through specialised light sensors within the eye. Photo / 123RF

Light from your phone will not damage your sleep as much as keeping a device next to your bed could, a leading Oxford University scientist has claimed.

Professor Russell Foster, director of the university's Sleep and Circadian Neuroscience Institute, said that brightness is "extremely unlikely" to affect sleeping patterns as screen lights are generally too weak.

Light exposure sets our circadian rhythm, or internal body clock, through specialised light sensors within the eye.

Research has previously suggested that the blue light produced by smartphones can delay the body's production of the sleep hormone melatonin.

But Prof Foster explained that the circadian rhythm is only disrupted when it's exposed to a large volume of light over a significant period of time.

The Royal Society Fellow instead said that "misleading" dark modes and screen filters on devices are making people believe that late-night phone use is not harming their sleep when it is.

Speaking at the European Society for Paediatric Endocrinology meeting in Vienna, Austria, he said: "I am not saying they shouldn't be used. I am saying that by simply saying: 'It's the light and not the use', it's misleading because kids are then saying: 'Oh I have got one of these devices which minimises the blue light, which means I am not going to shift my clock'.

Asked about dark modes and screen filters, Prof Foster said the light mode "probably was not" bright enough to do anything in the first place. Photo / 123RF

"Dusk light makes you go to bed later, and morning light advances the clock - it makes you want to get up earlier. So the argument has been that evening light via these devices delays the clock - makes you want to get up later. Whereas what is happening is, it is probably having very little effect on the clock, it is actually just giving you much-reduced sleep duration, so you're waking up tired."

Asked about dark modes and screen filters, Prof Foster said the light mode "probably was not" bright enough to do anything in the first place.

He added that it is still sensible to minimise light exposure before sleep to reduce levels of alertness and psychologically prepare for bed.