Wherever you are reading this – on the couch or in bed – there is a good chance that you are doing it on some sort of screen. According to a 2022 review, almost everyone upped their screentime during the Covid pandemic, and there is little evidence that use has gone back down. While that may or may not be bad for all sorts of reasons, a concern for many people is blue light, and whether its haunting glow is affecting our bodies in ways sunshine doesn’t. Could it somehow be bad light?
To start with the basics: blue light sits on the short-wave, high-energy end of the visible spectrum, close to the UV rays that can lead to provably harmful effects on the skin and retinas. In itself, this doesn’t mean anything – the sun has been bathing us in blue light since we were hunter gatherers – but concerns arise from the fact that many people stare at blue-light emitting devices for hours at a time, sometimes from mere inches away, often long after the sun has gone down.
Why might this be bad? Potential problems slot into three key areas, two of them interrelated: vision, sleep and broader health issues. Vision is potentially the most worrying – what if we have all been slowly destroying our eyes since the advent of smartphones? – but there is almost no evidence that this is a cause for concern. One of the studies most commonly cited to support the idea that blue light causes eye damage, for instance, consisted of researchers combining “retinal,” a chemical found in the eye, along with other cells, in a way that doesn’t occur in live human eyes. Elsewhere, studies on rats have shown that blue light might damage cells in the retina, but – once again – these studies were conducted in vitro, which means that they don’t tell us much (rats are also nocturnal, so may not react like humans to blue light – worth bearing in mind if you are concerned that excess tablet time might lead to early puberty). Human studies under realistic conditions are pretty much nonexistent because LED use is relatively new, but opthalmologists don’t see much cause for concern at present.
What about sleep? Here, there is slightly better evidence to consider. It is fairly well accepted that blue light boosts alertness and can improve cognitive function under certain circumstances – during the day when it is good to be alert. There’s also some evidence that it suppresses melatonin, but this is where misunderstandings may creep in. “Melatonin is not a ‘sleep hormone’, it’s actually a very mild modulator of sleep,” says Russell Foster, professor of circadian neuroscience at Oxford University. “And there’s no evidence that using blue light filters on your computer, for instance, has any effect upon the circadian system. In one of the best studies of its type, volunteers looked at an e-reader on its highest brightness for four hours, immediately prior to bedtime. They did this on five consecutive nights, at the end of which melatonin was suppressed, but sleep was delayed by just 10 minutes.” This may be statistically significant, but is biologically meaningless, says Foster. “It’s not that the e-reader had no effect upon biology – it just had almost no effect on sleep.”
This is crucial, because light-related sleep difficulty is where other health issues are sometimes thought to arise: a 2019 review of studies, for instance, suggests that light-related disruption to the sleep-wake cycle can cause moodiness or metabolic disruption, while one small study found links between exposure to light at night and certain cancers. But it seems likely that light exposure in general has a much more significant effect on sleep than blue light specifically. A recent paper suggests that the effects of blue light are counteracted if you have been exposed to even relatively dim light during the day. “You might get 500 lumens from an e-reader, but even a cloudy day in the UK is going to be 10,000 lumens or more,” says Foster. “So it seems as if normal light exposure by the environment is going to mitigate any subtle impacts at dusk or before bedtime.”
In other words, it is unlikely you are setting yourself up for serious health problems by occasionally flipping through an e-reader or going on a streaming bender before bed. You might experience eye strain from staring at a screen for too long – or stress yourself out by checking late-night emails – but your sleep is unlikely to suffer.
