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

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 (similar to 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. (C) 2016 The Author(s). Published by Elsevier B.V.