Elsevier

Sleep Medicine

Volume 23, July 2016, Pages 111-118
Sleep Medicine

Original Article
Two hours of evening reading on a self-luminous tablet vs. reading a physical book does not alter sleep after daytime bright light exposure

https://doi.org/10.1016/j.sleep.2016.06.016Get rights and content
Under a Creative Commons license
open access

Highlights

  • Evening reading on a tablet for two hours did not alter saliva melatonin levels.

  • Sleepiness, sleep onset latency, as well as sleep composition remained unaffected.

  • Tablet reading did not impact power spectral density during slow-wave sleep.

Abstract

Background

The use of electronic devices emitting blue light during evening hours has been associated with sleep disturbances in humans, possibly due to the blue light-mediated suppression of the sleep-promoting hormone melatonin. However, experimental results have been mixed. The present study therefore sought to investigate if reading on a self-luminous tablet during evening hours would alter sleepiness, melatonin secretion, nocturnal sleep, as well as electroencephalographic power spectral density during early slow-wave sleep.

Methods

Following a constant bright light exposure over 6.5 hours (~569 lux), 14 participants (six females) read a novel either on a tablet or as physical book for two hours (21:00–23:00). Evening concentrations of saliva melatonin were repeatedly measured. Sleep (23:15–07:15) was recorded by polysomnography. Sleepiness was assessed before and after nocturnal sleep. About one week later, experiments were repeated; participants who had read the novel on a tablet in the first experimental session continued reading the same novel in the physical book, and vice versa.

Results

There were no differences in sleep parameters and pre-sleep saliva melatonin levels between the tablet reading and physical book reading conditions.

Conclusions

Bright light exposure during daytime has previously been shown to abolish the inhibitory effects of evening light stimulus on melatonin secretion. Our results could therefore suggest that exposure to bright light during the day – as in the present study – may help combat sleep disturbances associated with the evening use of electronic devices emitting blue light. However, this needs to be validated by future studies with larger sample populations.

Keywords

Evening LED screen exposure
Saliva melatonin
Sleep
Power spectral density
Daytime light exposure

Abbreviations

BMI
body mass index
EEG
electroencephalography
PSG
polysomnography
EMG
electromyogram
EOG
electrooculogram
KSS
Karolinska Sleepiness Scale
LED
light emitting diode
N1 sleep
sleep stage 1
N2 sleep
sleep stage 2
REM
rapid eye movement
SWS
slow-wave sleep
SEM
standard error of mean
SD
standard deviation
SOL
sleep onset latency
SWA
slow-wave activity
TST
total sleep time
WASO
wake after sleep onset

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