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Light and Sleep

This page gives general information about blue light, LED lighting, eyes, and sleep. It was written by Michael Ten, who is not a licensed clinician, and it summarizes what reputable sources say, including where the evidence is mixed. If you have concerns about your eyes or sleep, please talk with a qualified healthcare provider.

Not medical advice: Nothing on this page is medical advice, diagnosis, or treatment. Please read the full disclaimer.

What blue light is

Blue light is the part of visible light with shorter wavelengths. According to the American Academy of Ophthalmology (AAO), the largest source of blue light in daily life is sunlight, and it also comes from fluorescent bulbs, LED lighting, and the screens of phones, tablets, and computers. Harvard Health notes that LED and compact fluorescent bulbs are more energy efficient than incandescent bulbs and also tend to produce more blue light.

Blue light and your eyes

The AAO says there is no scientific evidence that blue light from digital devices damages the eye, and that people get much less blue light from screens than from the sun. The AAO also says that less is known about blue light than about ultraviolet light and that its effects are still being researched.

The tired or dry feeling some people have after long screen sessions is most likely digital eye strain, according to the AAO, partly because people blink less while looking at screens. The AAO says eye strain does not cause lasting damage, and it describes the 20-20-20 rule: every 20 minutes, look at something at least 20 feet away for at least 20 seconds.

There is little evidence that blue light filtering glasses help with eye strain. The AAO does not recommend any special blue light blocking eyewear for computer use. A 2023 Cochrane review of 17 randomized trials found that these lenses may offer no short-term advantage for reducing eye strain from computer work, and that their effects on sleep are unclear because the existing evidence is inconclusive. Harvard Health is more open to them, suggesting that night shift workers and heavy evening device users consider them, so the picture for sleep is mixed.

Light, melatonin, and sleep

The evidence is stronger when it comes to sleep timing. Melatonin is a hormone the body releases at night as an internal signal of darkness. Harvard Health explains that light of any kind can suppress melatonin, and blue light at night does so more powerfully. In one experiment it describes, blue light suppressed melatonin for about twice as long as green light of similar brightness and shifted circadian rhythms by about twice as much.

In a study of 116 healthy young adults, Gooley and colleagues found that being in typical room light before bedtime, compared with dim light, delayed the start of melatonin in nearly every person tested and shortened the time melatonin was produced by about 90 minutes.

In a controlled study published in PNAS, Chang and colleagues found that when people read on a light-emitting tablet in the hours before bed, they took longer to fall asleep, released less melatonin, had a later body clock, and were less alert the next morning than when they read printed books. That study did not test e-ink readers, so it does not tell us directly how they compare.

The AAO agrees that too much blue light late at night from screens can make it harder to fall asleep, and Harvard Health adds that bright light during the day can support sleep at night.

LED streetlights

In 2016 the American Medical Association (AMA) adopted guidance for communities choosing among LED street lighting options. The AMA said LED street lighting brings cost and energy savings, but that conversions to improper LED technology can have adverse consequences, and its guidance aims to minimize potential harm to people and the environment.

General habits the sources mention

These come from the sources above and are general information, not treatment.

  • Take regular breaks from screens using the 20-20-20 rule described by the AAO.
  • Limit bright screens in the two to three hours before bed, which both the AAO and Harvard Health suggest.
  • Use dim red light for night lights, which Harvard Health says is less likely to shift circadian rhythm and suppress melatonin.
  • Keep a regular sleep schedule and turn off electronic devices at least 30 minutes before bedtime, as the CDC suggests.
  • Talk with a healthcare provider if you regularly have problems sleeping, which the CDC recommends.

Summary

Taken together, these sources suggest that evening light, and blue light in particular, can suppress melatonin and delay sleep, and the evidence for this is fairly strong. According to the AAO, current evidence does not show that blue light from screens damages the eyes, although research on long-term eye health is ongoing.

Sources