Don't look at a glowing screen in the hour before bed; read a paper book or an e-ink screen instead

Moderate value
Evidence B
Saves time
Free
Takes minutes
Long-term effort

In plain words

Reading on a glowing screen before bed means falling asleep about 10 minutes later than reading a paper book. Melatonin is suppressed by 55%. The next day the body clock is pushed back by more than 1.5 hours, so you are sleepier in the morning and take longer to wake up fully.

Cost: Free. Putting the phone down an hour before bed means working against habit over the long term, which takes willpower.
What you get: In a lab, the same people did both conditions in turn (a crossover trial). Reading a glowing e-book before bed made people fall asleep about 10 minutes slower than reading a paper book (25.7 minutes against 15.8 minutes). Evening melatonin was suppressed by 55%. The next day's body clock (circadian rhythm) was delayed by more than 1.5 hours, with melatonin starting to be released at 22:31 against 21:01. The next morning they were sleepier and took longer to wake up fully.
Notes: The number of people was small, and the conditions were tightly controlled in a lab. At everyday phone brightness and usage time, the effect may not be this large. How much a phone's night mode helps was not measured in this study.
Evidence grade: B : Supported by research but without a precise number, or based on small or single studies.
Sources: Chang, Aeschbach, Duffy & Czeisler (2015). Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness. PNAS. https://doi.org/10.1073/pnas.1418490112

Translated from the Chinese original. Original book, section 3, tip 8. Content may be out of date and rules differ by place. When you actually deal with an agency, a doctor or a court, follow what local officials, doctors and lawyers tell you. Disclaimer