Effects of smartphone use with and without blue light at night in healthy adults: A randomized, double-blind, cross-over, placebo-controlled comparison.
Level 2 - randomized trial
Randomized, double-blind, crossover, placebo-controlled clinical trial
PubMed 28017916 · doi:10.1016/j.jpsychires.2016.12.010
What was done
In a randomized, double-blind, placebo-controlled crossover study involving two 3-day admissions, 22 healthy adults played smartphone games for 150 minutes (7:30 to 10:00 PM) using either a conventional LED display or a blue light-suppressed screen, later crossing over to the alternate condition. Investigators measured serum melatonin (hourly), serum cortisol and body temperature (every 120 minutes), along with psychiatric and performance metrics: Profile of Mood States (POMS), Epworth Sleepiness Scale (ESS), Fatigue Severity Scale (FSS), and auditory and visual Continuous Performance Tests (CPTs).
What was found
Compared to blue-suppressed light, nighttime use of conventional blue light smartphones resulted in significantly decreased subjective sleepiness (Cohen's d = 0.49, Z = 43.50, p = 0.04), decreased confusion-bewilderment scores (Cohen's d = 0.53, Z = 39.00, p = 0.02), and increased commission errors on performance testing (Cohen's d = -0.59, t = -2.64, p = 0.02). Time to reach 50% dim light melatonin onset was longer with blue light (2.94 vs. 2.70 hours), though changes in body temperature, serum melatonin levels, and cortisol levels did not reach statistical significance.
Why it matters
The findings provide experimental evidence that blue light emitted from smartphones acutely increases nighttime alertness and reduces impulse control/sustained attention precision, even without statistically significant endocrine suppression.
Limits
The study had a small sample size of 22 healthy adults and evaluated a single 150-minute continuous gaming session, limiting generalizability to real-world varied screen habits. Key physiological and hormonal endpoints (melatonin, cortisol, body temperature) did not show statistically significant differences between conditions.
Cited by
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