How bad is screen light in the evening for my sleep?
Screen light in the evening disrupts your sleep hormone and keeps you less sleepy at the wrong moment. Dim your screens after dinner, or wear amber-tinted glasses if you still need to work.
Two hours of exposure to the bluish light from a screen (wavelengths around 460 nanometres) in the evening suppresses your production of melatonin, the hormone that signals to your body that it is time to sleep. The brighter the screen, the stronger that effect. Good news: once you turn the screen off, melatonin production typically recovers within fifteen minutes.
Five hours of working in front of a display with extra blue light not only makes people objectively less sleepy, but also more alert on attention and memory tasks. That sounds convenient, but it also means your brain is in a wakefulness mode at exactly the wrong moment, making it harder to fall asleep.
Smartphone use for 150 minutes in the evening presents a more mixed picture. You do feel less sleepy than when blue light is filtered out, but blood melatonin levels did not differ significantly between the two groups in that study. This suggests that the effect of a phone screen is smaller than that of a bright desk lamp or computer monitor, yet still noticeable.
Plain white screen surfaces are, incidentally, more problematic than you might think: white light with mixed colours suppresses melatonin more strongly than pure blue light at the same level of blue-sensitive light signals. Filtering blue light therefore helps, but does not fully solve the problem.
Wearing amber-tinted glasses (which block blue light) for two hours before bedtime improved both sleep quality and total sleep duration in people with sleep problems, as shown in a small study with 14 participants. It is a simple, inexpensive measure that appears worthwhile, especially if you have difficulty falling asleep. Also keep in mind that the timing of exposure is at least as important as the amount: during the day, blue light is actually beneficial for your alertness and your biological clock.
Based on multiple controlled studies, including experiments with precisely defined exposure durations (2 hours, 5 hours, 150 minutes) and a small randomised study on blue-light-blocking glasses (n=14). The strength of evidence varies by sub-question: melatonin suppression by blue light is well established; smartphone-specific effects are less clear-cut.
Does a blue-light filter on my phone really affect my sleep?
A blue-light filter on your phone probably has little effect on your sleep. If you really want to improve your sleep through light, switch your home lighting to warm yellow in the evening instead of cool white.
Is it a problem that I often wake up during the night?
Waking up occasionally is normal, but if it happens frequently and affects you during the day, there may be an underlying cause such as sleep apnea or PTSD. In that case, have it checked out.
Does a consistent morning routine with daylight help you fall asleep more easily in the evening?
A consistent morning routine with daylight helps sharpen your biological clock, allowing you to fall asleep earlier and more easily in the evening. The evidence is not perfect, but consistent enough to make it worthwhile: step outside briefly shortly after waking up.
How much sleep do I really need?
Seven to eight hours per night is the best-supported target range for adults. If you are consistently sleeping fewer than 7 hours, getting more sleep is not a luxury but a serious investment in your health.
Does a cool, dark bedroom really help you sleep better?
A bedroom temperature of 20 to 25 degrees combined with good ventilation demonstrably improves your sleep. This effect is greatest for older adults, and above 25 degrees sleep quality deteriorates quickly.
Does the menopause disrupt my sleep, and what can help?
The menopause genuinely disrupts your sleep, primarily through hot flashes and hormonal changes. Cognitive behavioural therapy for insomnia (CBT-I) is the best first step; hormone therapy or melatonin may come into the picture after that.