Blue-light glasses: what the research shows

Less tired eyes at the screen, protection for the retina, better sleep: these are the three promises that often come with blue-light filtering lenses. Such lenses use a dye or a reflective coating to hold back part of the short-wavelength blue light. How much depends on the product: according to Sumeer Singh, lead author of the Cochrane review described below, the usual blue-light filtering lenses block roughly 10 to 25 per cent of blue light. What does that achieve? Research now offers some answers – and shows where the gaps still are.

The Cochrane review: 17 trials, little benefit

Cochrane reviews systematically pool the available studies on a question. For the 2023 review on blue-light filtering lenses, an international team led by Sumeer Singh and Laura Downie identified 17 randomised trials involving a total of 619 adults. Each trial compared filtering lenses with standard lenses.

The eye-strain finding rests mainly on a trial of 120 people who worked at a computer for two hours: the filtering lenses offered no advantage, either for symptoms or for an objective marker of fatigue, the so-called critical flicker-fusion frequency. Two smaller trials (46 people combined) also found no difference.

The six sleep trials mostly tested strongly tinted amber or orange lenses worn in the evening, usually by people with sleep problems, depression or bipolar disorder. Some of these lenses block well over half of blue light and are hardly comparable with ordinary everyday lenses.

The trials lasted from less than a day to five weeks, so they tell us nothing about long-term effects, for example on the retina. Unwanted effects were reported infrequently.

How much blue light actually comes from screens?

Daylight provides by far the larger share of blue light: according to Sumeer Singh, screens supply our eyes with only around one thousandth of the blue light that daylight does.

In 2016, scientists at Public Health England, the English public health agency at the time, measured energy-saving light bulbs, computers and tablets: even when viewed for long periods, none of the sources came close to international exposure limits.

The American Academy of Ophthalmology (AAO), the professional body for eye physicians and surgeons in the United States, states that there is no scientific evidence that blue light from digital devices damages the eyes. It therefore does not recommend blue-light glasses.

During the day, bright light with plenty of blue is actually desirable: according to an international expert group, more daytime light can – depending on the study – improve alertness, performance, mood or sleep.

Why your eyes still get tired at the screen

Burning, dry or tired eyes after a long day at the screen – known as digital eye strain – are nonetheless real. The Cochrane review notes that complaints such as tired or sore eyes, headaches, blurred vision and dry eyes have been described in up to 90 per cent of computer users. But the causes lie elsewhere:

• Blinking less: we normally blink about 15 times a minute, but at a computer only about 5 to 7 times, according to the AAO. This can leave the eyes dry and irritated.
• Constant focusing: at close range, your eyes have to keep adjusting their focus – according to the AAO, a strain similar to long periods of reading, writing or sewing.
• Brightness: if the screen is brighter than its surroundings, your eyes have to work harder.
• Uncorrected vision problems: an uncorrected refractive error or early presbyopia can add to the strain.

In the AAO’s view, then, the problem lies in our screen habits rather than in the light the devices give off. You can read more in our guide on dry eyes and screen work.

Evening light and sleep: a more complex picture

The retina contains special light-sensitive nerve cells that are involved less in seeing than in other tasks: among other things, they influence the body clock, melatonin release and pupil size. Their light sensor, melanopsin, responds most strongly to light at around 480 nanometres – in the blue range.

A 2015 laboratory experiment in the USA showed how strongly screen light can act in the evening. Twelve young adults read on a tablet for about four hours on five evenings – and, for comparison, from a printed book. While they were reading on the tablet, their evening melatonin was suppressed by around 55 per cent (measured on the fifth evening). They took about ten minutes longer on average to fall asleep, had less REM sleep and felt sleepier the next morning. Their body clock shifted too: the following evening, melatonin rose more than one and a half hours later than after reading the printed book. The tablet was set to full brightness in an otherwise very dimly lit room. The researchers did, however, consider four hours of evening screen time realistic.

In its recommendations, published in 2022 in the journal PLOS Biology, the expert group mentioned above also gives guidance for the evening: in at least the three hours before bedtime, light at the eye should be dim – no more than 10 lux melanopic EDI (melanopic equivalent daylight illuminance). This measure reflects how strongly light stimulates the melanopsin cells. While you sleep, the room should be as dark as possible – no more than 1 lux, again as melanopic EDI. According to the experts, a screen on its own can exceed the evening value more than sixfold; simply changing the screen colour, for example with night mode, reduces the relevant radiation by only about half.

Whether tinted evening glasses improve sleep remains an open question according to the Cochrane review. The AAO advises avoiding screens where possible in the two to three hours before bed.

What helps instead

• 20-20-20 rule: every 20 minutes, look at something at least 20 feet (just over 6 metres) away for at least 20 seconds, as the AAO recommends.
• Blink deliberately, and use artificial tears if your eyes feel dry.
• Distance and position: place the monitor about an arm’s length away (around 64 centimetres), with your gaze slightly downward.
• Brightness: match the screen brightness to your surroundings and increase the contrast if anything; a matte screen filter can cut glare.
• Room air: in a dry, warm room a humidifier can help; if you wear contact lenses, you can switch to your glasses from time to time.
• In the evening: dim the screen, use night mode only as an extra and keep room lighting low.
• During the day: get plenty of bright light, ideally daylight.

Don’t confuse blue-light glasses with computer glasses: the latter are prescription glasses whose lenses are set for the intermediate distance of around 51 to 66 centimetres, sometimes as multifocal lenses. According to the AAO, they can reduce eye strain during long computer sessions – and they have nothing to do with blue-light filters.

When to have your eyes checked

If your symptoms do not improve despite breaks and a good set-up, the AAO advises having your eyes examined by an ophthalmologist. Persistent symptoms may be caused by dry eye or an uncorrected refractive error, for example. The ophthalmology service at My Laser Vision in Wallisellen includes, among other things, an eye examination for screen work and an assessment of the tear film.

Things are different if symptoms come on suddenly: if an eye starts to hurt, turns red, becomes sensitive to light or your vision in that eye becomes blurred, there may be a serious cause – for example an inflammation of the cornea (keratitis), which is most common in people who wear contact lenses. In that case, the AAO advises contacting an ophthalmologist straight away rather than waiting; untreated keratitis can lead to lasting loss of vision.

The bottom line: for tired eyes at the screen, experts rely on breaks, blinking and the right prescription rather than filtering lenses – and for sleep, what counts above all is how bright your evening is overall, not just how blue.