Blue light filters and sleep: do screens and glasses matter?

The short answer

• ≈10min

  Longer to fall asleep after evenings of reading on a bright iPad instead of a paper book (12 adults)

• 1.5h

  How much later their body clock ran after five evenings of iPad reading

• 10lux

  The most body-clock light experts advise in the 3 hours before bed

• 3of 6

  Small trials of blue-blocking glasses that reported better sleep. The other 3 found no clear difference.

Key findingYour body clock reacts to how much light reaches your eyes in the evening, not just its colour. Experts advise dim light for the 3 hours before bed, and darkness while you sleep. A filter may help a little, but it is not enough on its own.

What is blue light, and why does it matter at night?

Light comes in many colours. Blue light is the part of the light we can see that has short waves. Daylight is full of it, and so is the light from many screens. The light from the iPad in one study peaked in the blue range.

Your eyes have special cells that tell your body clock whether it is day or night. These cells react most to blue-green light. In the evening, light on them holds back melatonin, a hormone that helps you feel sleepy. It also pushes your body clock later, so you feel sleepy later.

So colour matters, but so does brightness. Experts now measure evening light in “melanopic lux”. This counts light by how strongly it acts on those cells, so blue-ish light counts for more.

What reading on a tablet before bed did

In a well-known 2015 study, 12 healthy young adults lived in a sleep lab for two weeks. On five evenings they read on an iPad at full brightness, and on five they read a printed book. They read for about 4 hours before a 10 p.m. bedtime, in a very dim room.

After iPad evenings, they took nearly 10 minutes longer to fall asleep. Their evening melatonin was cut by 55%, while the book didn’t cut it at all. Their body clock ran 1.5 hours later. They had about 12 minutes less REM (dream) sleep (our calculation). They felt less sleepy at bedtime, but sleepier the next morning.

There are caveats. Four hours at full brightness, in an otherwise very dim room, is a strong dose of screen light. The study had no dim or warm-coloured screen to compare, so the authors say brightness, not blue light, may explain the effect. Total sleep didn’t change, but everyone stayed in bed for exactly 8 hours.

Blue light filters and sleep: do phone filters work?

Many phones have a setting that cuts blue light in the evening, such as Night Shift on the iPhone. A 2021 trial put 167 students aged 18–24 into three groups by chance. For a week, in the hour before bed, one group used an iPhone with Night Shift on. One used it with Night Shift off, and one used no phone. Wrist sensors tracked their sleep.

There were no clear differences between the three groups. In an extra check of students who usually slept more than 6.8 hours, those with no phone slept best. For them, putting the phone away beat using it with Night Shift on.

A 2023 lab study tested the idea behind filters more strictly. Researchers built a special screen that could cut the body-clock part of its light about three times over. It still looked just as bright and the same colour. 72 healthy young men sat at it for 3.5 hours before bed.

With less body-clock light, the men felt sleepier and made more melatonin. But they fell asleep faster only at the brightest screen setting. Across all the settings, the total dose of body-clock light mattered most.

Experts say the colour settings on ordinary screens cut body-clock light only by about half. They advise using a filter together with a dimmer screen and dim room lights.

Do blue light glasses work for sleep?

Blue light glasses have lenses that filter out part of the blue light. In 2023, a Cochrane review, a careful review of all the trials on one question, looked at 17 trials with 619 people. Six of the trials, with 148 people in total, checked sleep.

Three small trials reported better sleep and three found no clear difference. The three that gave numbers the review could use were the ones with no clear difference. The trials studied very different people, from athletes to people with insomnia, depression or bipolar disorder. None of them measured melatonin in the blood.

Side effects were uncommon but included headaches, discomfort and lower mood. On eye strain from computers, the same review found the glasses may make no difference.

How much light is too much in the evening?

In 2022, a panel of 18 light and sleep experts published simple targets for healthy adults. They measured light at the eye in melanopic lux.

This is easier than it sounds. Evening light in a typical home is about 30 lux, and with warm white bulbs that can already meet the target. In one study of homes, nearly half of the evening readings already did. A screen on its own, with no other light, can give more than 60 melanopic lux.

Daylight matters too. Bright light during the day may soften the effect of light in the evening. People also differ a lot. Some react to evening light more than 10 times as strongly as others, and children react more than adults. Experts add that a regular daily pattern of light and dark helps your body clock; see how to fix your sleep schedule.

Claims and evidence

• ClaimNight Shift or a blue light filter protects your sleep.

  EvidenceIn 167 students, Night Shift made no clear difference to sleep over a week. In the lab, cutting body-clock light from a screen helped only a little.

• ClaimBlue light glasses are proven to improve sleep.

  EvidenceSix small trials disagree, and a 2023 Cochrane review rated the evidence very low certainty.

• ClaimOnly the colour of the light matters.

  EvidenceHow much light reaches your eyes matters too. In the iPad study, the authors say brightness may explain the effect.

• ClaimLight only matters at night.

  EvidenceExperts advise bright light by day, at least 250 melanopic lux. Brighter days may soften the effect of evening light.

What this means for you

What the research can’t tell you yet

• Small lab studies. The key experiments tested 12 adults and 72 young men, over a few evenings.
• Real-life filters. We found only one trial of a phone filter where people were put into groups by chance. It lasted one week, in students.
• Glasses. The six sleep trials were small and short, in very different groups.
• Teenagers and older adults. Most people studied were young adults. Experts expect children to react more strongly to evening light.

How Bodyvault uses this research

If you turn on nudges, Bodyvault reminds you to wind down 45 minutes before bed: dim the lights and put the phone away. You can set this from 15 to 90 minutes, though experts suggest keeping light low for 3 hours. Five minutes before bed, a second reminder says screens off. The check-in can ask about screens or books in bed and time outdoors, and “Your data shows” compares these with your sleep.

General information about fitness and nutrition, not medical advice. If you have a health condition, are pregnant or take medication, talk to your doctor before changing your diet or training.