The reason our screens may not be shifting our body clock, Foster explains, is that the level of blue light exposure from screens is just not strong enough. For example, the light from an iPhone or Kindle is 10-30 lux (that is, lumens per sq m). The sun emits a whopping 80,000-100,000 lux. So it’s not the blue light therefore that’s preventing us from getting shut-eye, it’s the emails, the Reels, the gaming, the TikTok? “Exactly,” he says. “Devices should not be used for at least 30 minutes before bedtime – not because of the light but because of the alerting activity the content creates in the brain.”
The impact on eye health
But how bad are our screens for actual eye health? I spoke to Prof Glen Jeffery, professor of neuroscience at UCL’s Institute of Opthalmology, who has been doing a great deal of (as yet unpublished) work recently on the impact of blue light on our eyes. “There are particular types of blue light,” he says, “present in expensive car lights, overhead motorway lights and some state-of-the-art TVs, that can be particularly damaging to eyes.”
He explains, “You have more mitochondria in your retina than any part of the human body. These are like batteries, providing energy to the cell, but they absorb blue light which can cause them to shut down.” Jeffery’s colleagues at UCL have been conducting studies on growing cells under blue light and they can confirm that cells aren’t happy there. “They don’t tend to divide well and some of them die easily,” he says.
He goes on to say that our screens and phones don’t emit these dangerous levels of intense blue light. However, this is not to say that low levels of blue light from our screens don’t have a cumulative effect on eye health over time – these devices haven’t been around long enough to enable long-term studies.
And what about the oscillation of light from our smartphones that some say causes headaches and eye strain? Research published in the National Library of Medicine in 2017 shows that blue light lenses can help to block this. However that is all dependant on whether your blue light glasses actually contain the filter they claim they do.
Jeffery and his team have been testing lenses with a spectrometer to measure the light coming out the other side and while some did block the blue light, many, he warns, did absolutely nothing and contained no filter whatsoever. It is therefore important if you are going to get a pair that you choose a brand, such as Ocushield, that is FDA- and MHRA-approved and third-party tested.
Jeffery does tell me, though, that within our retina we have a natural filter to blue light, a macular pigment in the form of a yellow spot. “This filter varies enormously from person to person, but its level of protection depends on whether you eat enough vegetables,” he says. “You can help reduce the probability of developing age-related macular degeneration by eating a more plant-based diet.”
So should I ditch the blue light glasses and spend the money on more trips to the grocery store? “100 per cent,” he says.
Read last week’s article: Fact or fad: Are vitamin drips worth the effort?