Bright light alone or combined with caffeine improves sleepiness in chronically sleep-restricted young drivers

Young drivers are over-involved in sleepiness-related crashes. The alerting effects of bright light offer a potential countermeasure for driver sleepiness, either replacing or in conjunction with current countermeasures such as the use of caffeine.

Thirty young (18-25) chronically sleep-restricted drivers drove in a simulator under randomized conditions of continuous bright light ('Light,' 500 nm, 230μw/cm²), caffeine ('Caffeine,' 100 mg caffeinated gum), or light and caffeine together ('Light + Caffeine'), after driving under a placebo condition ('Placebo,' decaffeinated gum, 555 nm light, 0.3 μW/cm²) on three consecutive days. Using mixed-effects linear models, the associations between these conditions and physiological outcomes (EEG alpha and theta power, heart rate, and beat-to-beat intervals), driving performance (lateral lane and steering-related outcomes and lateral acceleration), and subjective sleepiness was assessed.

Relative to Placebo, all conditions improved driving performance outcomes (P < 0.0001), with effects of Light + Caffeine equal to Light but greater than Caffeine. Light + Caffeine reduced EEG alpha power more than Light or Caffeine (P < 0.0006), but ECG outcomes were generally worse under all conditions relative to Placebo. Subjective sleepiness improved under the Light + Caffeine condition only (P < 0.0001).

Combining bright light and caffeine enhances their alerting effects on lateral lane variability and subjective sleepiness. A bright light could be a practical alternative to caffeine for sleepy drivers who avoid caffeine. The alerting effects of bright light could alleviate chronic community-level mild sleep restriction and provide on-road benefits to reduce severe injuries and fatal sleepiness-related crashes.