A Blue-Enriched, Increased Intensity Light Intervention to Improve Alertness and Performance in Rotating Night Shift Workers in an Operational Setting

PURPOSE: This study examined the efficacy of a lighting intervention that increased both light intensity and short-wavelength (blue) light content to improve alertness, performance and mood in night shift workers in a chemical plant. PATIENTS AND METHODS: During rostered night shifts, 28 workers (46.0±10.8 years; 27 male) were exposed to two light conditions each for two consecutive nights (~19:00–07:00 h) in a counterbalanced repeated measures design: traditional-spectrum lighting set at pre-study levels (43 lux, 4000 K) versus higher intensity, blue-enriched lighting (106 lux, 17,000 K), equating to a 4.5-fold increase in melanopic illuminance (24 to 108 melanopic illuminance). Participants completed the Karolinska Sleepiness Scale, subjective mood ratings, and the Psychomotor Vigilance Task (PVT) every 2–4 hours during the night shift. RESULTS: A significant main effect of time indicated KSS, PVT mean reaction time, number of PVT lapses (reaction times > 500 ms) and subjective tension, misery and depression worsened over the course of the night shift (p<0.05). Percentage changes in KSS (p<0.05, partial η(2)=0.14) and PVT mean reaction time (p<0.05, partial η(2)=0.19) and lapses (p<0.05, partial η(2)=0.17) in the middle and end of night shift, expressed relative to start of shift, were significantly improved during the lighting intervention compared to the traditional lighting condition. Self-reported mood did not significantly differ between conditions (p>0.05). CONCLUSION: Our findings, showing improvements in alertness and performance with exposure to blue-enriched, increased intensity light, provide support for light to be used as a countermeasure for impaired alertness in night shift work settings.