Effects of light exposure on psychomotor vigilance in shift workers: a systematic review.

STUDY OBJECTIVES: Circadian misalignment caused by shift work has been linked to fatigue and diminished psychomotor performance. Light, the major zeitgeber of circadian rhythms, has been investigated in studies, particularly regarding the spectral composition's effect on vigilance. This review explores whether light interventions improve reaction times and reduce errors such as false starts and lapses among shift workers. METHODS: Following PRISMA guidelines, a systematic search was conducted in PubMed, PsycINFO, Scopus, and Web of Science. The Cochrane Risk of Bias 2 tool and ROBINS-I tool were used to assess the risk of bias. We included peer-reviewed studies that provided descriptions of lighting conditions, including illuminance (in lx), color temperature (in K), and melanopic equivalent daylight illuminance (in MEDI lx). The primary outcome was mean reaction time, with secondary measures including lapses, false starts, and 10% fastest and slowest reaction times. Differences in light parameters (lx, K, and MEDI lx) between the intervention and control groups were summarized narratively. Ratios of intervention to control values were calculated, adjusting for exposure duration. RESULTS: The search resulted in 3,120 records, of which 25 studies met inclusion criteria. Ten studies reported significant association between reaction times and lighting. Light exposures of at least 5 hours, combined with a minimum difference of 159 MEDI lx, were associated with a statistically significant improvement in reaction times. CONCLUSION: Extended light exposure combined with a higher melanopic gradient appears to enhance psychomotor vigilance. However, heterogeneity in study design and reporting of intervention studies limits the certainty of this conclusion.