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

Abstract

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.

The photobiology of the human circadian clock

“…For example, blue light is usually filtered out in electronic screens during the night, 18,19 and blue-enriched light is used by night shift workers to optimize their body rhythm for achieving maximum performance. [20][21][22] The ability to directly image the human SCN in vivo has been severely limited due to its small size and the relatively low spatial resolution provided by medical imaging devices. Previous functional magnetic resonance imaging (fMRI) studies using 3-Tesla (3T) scanners were restricted to recording the "suprachiasmatic area", which encompasses a large part of the hypothalamus and thus includes many other potentially light-sensitive nuclei.…”

The photobiology of the human circadian clock

“…Thus, current guidelines regarding the use of artificial light are based solely on the clock’s sensitivity to blue light. For example, blue light is usually filtered out in electronic screens during the night ( 18 , 19 ), and blue-enriched light is used by night shift workers to optimize their body rhythm for achieving maximum performance ( 20 – 22 ).…”

Optimizing Real-Time Wellness Intervention Studies in Healthcare Shift Workers: Outcomes from a Prospective, Single-subject Design Study of a Digital Sleep Aid

“…Self-reporting subjective outcome data is a common practice in sleep intervention studies performed in real-world populations. [15][16][17] Here, outcome measures of daily sleepiness, last nights' sleep quality, and daily tension were manually reported by participants via brief daily surveys delivered by text message. Even among participants who used the earbuds in the study, consistency with filling out daily surveys was lacking.…”