Light hygiene: Screen time before bed hurts sleep quality

Exposure to short-wavelength light in the evening and at night has a negative effect on sleep, leading to worse sleep quality and daytime functioning, according to a new study.

“[W]e provided further evidence that evening and night-time exposure to screens of media devices may have harmful effects on subjectively perceived sleep quality and daytime functioning in a cohort of healthy individuals, with small-to-medium effect sizes,” researchers said. “We also showed that limiting evening exposure length may be beneficial in terms of various sleep and sleep-related parameters.”

The 693 healthy participants (mean age, 31.2±11.4 years; 538 women) logged a mean evening television time of 1.15±1.69 hours, while the average use of their computers or mobile phones were 3.76±2.97 and 3.47±3.35 hours, respectively. Overall, the mean time spent on screen-based devices was 8.38±5.31. [Sleep Health 2020;6:498-505]

General linear models showed that cumulative light exposure had a significant impact on sleep inertia (p=0.019) and sleep latency during workdays (p=0.038). Those who had greater exposures tended to take longer to fall asleep and feel more tired and less alert the following day. No such interactions were reported for other sleep outcomes, such as sleep duration and social jet lag.

Because the cumulative evening screen time may be too arbitrary of a variable, the researchers then examined the impact of exposure 90 minutes before going to sleep. The effect on sleep inertia remained significant (p<0.001), such that those who were not on their devices within this window felt more energized and alert the next morning.

On the other hand, those who were exposed to their device screens 90 minutes before bed had greater social jetlag (p<0.001) and fatigue (p=0.032).

Overall subjective sleep quality, as measured by the Pittsburgh Sleep Quality Index (PSQI), did not differ between the two use groups, but significant differences in the domains of habitual sleep efficiency (p=0.006) and daytime dysfunction (p<0.001) were observed, both in favour of no screen use before bedtime.

Notably, the researchers also sought to determine whether the use of blue-light filters had an effect on sleep parameters. Seventy-four participants (10.6 percent) reported using filters. They demonstrated no significant benefit on outcomes, though there was a trend toward better sleep duration on workdays (p=0.058).

“The aim of our study was to test healthy population for the use of screen-based devices during evening and night hours and its association with subjectively perceived sleep quality and other sleep-related parameters,” the researchers said.

“Despite the lack of direct light exposure-related parameters in the present study, we think that the study design adds value to the research topic of the impact of evening/night-time artificial screen light on sleep and next-day functioning, as it considers multiple subjective sleep-related parameters and a large sample that would've been otherwise hard to reach with the application of more direct-objective measurements,” they added.