Two hours of evening reading on a self-luminous tablet vs. reading a physical book does not alter sleep after daytime bright light exposure.
Level 2 - randomized trial
Randomized crossover trial
PubMed 27539026 · doi:10.1016/j.sleep.2016.06.016
What was done
In a randomized crossover trial, 14 participants (6 females) underwent 6.5 hours of daytime bright light exposure (~569 lux) and then read a novel for two hours (21:00–23:00) either on a self-luminous tablet or as a physical book. One week later, participants crossed over to the alternate reading medium. Assessed outcomes included serial evening salivary melatonin concentrations, polysomnography-recorded sleep (23:15–07:15), pre- and post-sleep sleepiness, and electroencephalographic power spectral density during early slow-wave sleep.
What was found
The study found no differences in sleep parameters or pre-sleep salivary melatonin levels between the tablet reading and physical book reading conditions. No exact numerical values or effect estimates were provided in the abstract.
Why it matters
The findings suggest that sufficient daytime bright light exposure may protect against the sleep disturbances and melatonin suppression typically linked to evening screen use.
Limits
The sample size was very small (n=14), raising the risk of false negatives. The study tested an artificial protocol involving 6.5 hours of constant bright light (~569 lux) that may not reflect standard daily indoor lighting. No numerical data or statistical measures were reported in the abstract.