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Evening Electronic Book Light Damages Sleep (study summary)


Proceedings of the National Academy of Sciences of the USA
Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness

Anne-Marie Chang, Daniel Aeschbach, Jeanne F. Duffy, and Charles A. Czeislera

September 24, 2014


Noting that sleep quality has been declining for 50 years, reseachers wanted to check on the the contribution of blue light emitting devices to the problem.

90% of Americans use their electronics within one hour of going to sleep.  They use them anywhere from 3 to nights a week, on average.

Studies have shown that blue light impairs sleep. The study looked at how blue light eReaders affects sleep, melatonin, and alertness.


Using a blue light emitting eReader within four hours of going to sleep will produce a cycle of poor sleep and drowsiness.

The blue light will:

  • impair circadian rhythm
  • decrease melatonin levels
  • create a longer time to fall asleep
  • decrease subjective sleepiness
  • decrease delta/theta brainwaves
  • reduce waking alertness


All subjects stayed in a dimly lit room for 5 nights. They read during the four hours prior to going to sleep.

The first group used a blue light emitting eReader. The second group read a printed book.

Researchers recorded subjects as follows:

    • melatonin levels
    • time to fall asleep
    • total sleep time
    • time spent in each sleep stage
    • self-reported sleepiness


Sujects using eReaders projecting lue light formed delays in their circadian clocks.

They had an average 20% drop in their melatonin compared to non-eReader use nights.

Compared to controls, eReader users took 10 minutes longer to fall asleep. Users had approximately 11 minutes less REM sleep.

Except for the above findings, the , the eReader users had a similar total time asleep, and a similar time in each sleep stage, as compared to controls.



Researchers found that night time eReader use prolonged the time it takes to fall asleep.

Users’ circadian clocks were delayed, and their melatonin was suppressed until the following morning.

When they did awake, their melatonin levels rose above normal.

This means that subjects were awake at night, and sleepy during the day.

The following day, users were also less alert.

The habitual use of light emitting devices at night can create a long-standing insomnia pattern.