Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness
- aDivision of Sleep and Circadian Disorders, Departments of Medicine and Neurology, Brigham and Women's Hospital, Boston, MA 02115;
- bDivision of Sleep Medicine, Harvard Medical School, Boston, MA 02115; and
- cInstitute of Aerospace Medicine, German Aerospace Center, 51147 Cologne, Germany
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Edited by Joseph S. Takahashi, Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, TX, and approved November 26, 2014 (received for review September 24, 2014)
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Fig. 1.Representative raster plot of the 14-d study protocol. Black bars indicate the 10:00 PM–6:00 AM sleep episode in darkness. Gray bars denote dim room light (∼3 lx of white light in the angle of gaze; Materials and Methods), and white bars denote typical indoor room light (∼90 lx in the angle of gaze). Striped bars show the constant posture (CP) procedures. Reading sessions are marked either by the LE-eBook or the print-book and symbols. Participants were randomized to the order of reading condition. Ambient room light level for all reading sessions was dim (∼3 lx).
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Fig. 2.Melatonin suppression (A and B) and phase shifting (C and D) during and after the LE-eBook and print book reading conditions. (A) Average waveforms of melatonin (±SEM) during the fifth night of each reading condition. The black bar denotes the scheduled sleep episode (22:00–06:00). (B) Percent suppression for each condition for each participant (filled symbols) and group average (±SEM; open symbols). (C) Average waveforms of melatonin (±SEM) on the evening/night after each reading condition. (D) Average phase shift of melatonin onset for each condition for each participant (filled symbols) and group average (±SEM; open symbols). The main effect of Condition was significant (P < 0.05, mixed model).
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Fig. 3.Sleep and sleepiness/alertness measures during and after the print-book and LE-eBook reading conditions. (A) Mean (±SEM) sleep latency to stage N2 in minutes for each reading condition. *P = 0.009, mixed model. (B) Mean (±SEM) accumulation of REM across 8-h sleep episode for each condition. *P = 0.029. (C) Mean duration (in minutes) of sleep stages N1 (white), N2 (light gray), N3 (dark gray), and REM (patterned), and total sleep time (TST; numbers at top of bar) for each reading condition. *P = 0.029. (D) Mean (±SEM) alertness ratings (circles) during and on the morning after each reading condition with respect to clock hour. Mean delta/theta activity in the waking EEG, power density in the 1.0–7.5 Hz range (squares), that was derived from C3/M2 during the fourth and fifth reading sessions of each condition is also shown. (E) Power density in the waking EEG during the LE-eBook condition (open circles) expressed as a percentage of the printed-book condition (100%; dashed line). Two-way mixed-model ANOVA on log-transformed absolute power densities per 0.5-Hz was significant for condition (P < 0.04). Filled triangles at the bottom indicate EEG frequency bins for which the difference between conditions was significant (P < 0.05, post hoc paired t tests).
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Fig. 4.Spectral radiometric profile of the LE-eBook device (gray) and incident light reflected by the printed book (black). The peak irradiance for the LE-eBook eReader is ∼450 nm and for the reflected light is 612 nm.
