Abstract
Light can be used to facilitate alertness, task performance and circadian adaptation during night work. Novel strategies for illumination of workplaces, using ceiling mounted LED-luminaires, allow the use of a range of different light conditions, altering intensity and spectral composition. This study (ClinicalTrials.gov Identifier NCT03203538) investigated the effects of short-wavelength narrow-bandwidth light (λmax = 455 nm) compared to long-wavelength narrow-bandwidth light (λmax = 625 nm), with similar photon density (~2.8 × 1014 photons/cm2/s) across light conditions, during a simulated night shift (23:00–06:45 h) when conducting cognitive performance tasks. Light conditions were administered by ceiling mounted LED-luminaires. Using a within-subjects repeated measurements study design, a total of 34 healthy young adults (27 females and 7 males; mean age = 21.6 years, SD = 2.0 years) participated. The results revealed significantly reduced sleepiness and improved task performance during the night shift with short-wavelength light compared to long-wavelength light. There was also a larger shift of the melatonin rhythm (phase delay) after working a night shift in short-wavelength light compared to long-wavelength light. Participants’ visual comfort was rated as better in the short-wavelength light than the long-wavelength light. Ceiling mounted LED-luminaires may be feasible to use in real workplaces, as these have the potential to provide light conditions that are favorable for alertness and performance among night workers.
Highlights
At the beginning of this century it was established that humans have nonvisual photic input from a subset of intrinsically photosensitive retinal ganglion cells expressing the photopigment melanopsin, which is maximally sensitive to short-wavelength light [1,2,3]
The current study revealed beneficial effects of exposure to short-wavelength narrow-bandwidth light, compared to photon matched (~2.8 × 1014 photons/cm2/s) long-wavelength narrow-bandwidth light, on subjective alertness and task performance during a simulated night shift
The participants’ melatonin onset was more phase delayed in short-wavelength light compared to long-wavelength light
Summary
At the beginning of this century it was established that humans have nonvisual photic input from a subset of intrinsically photosensitive retinal ganglion cells (ipRGCs) expressing the photopigment melanopsin, which is maximally sensitive to short-wavelength light [1,2,3]. These ipRGCs project directly to the main circadian pacemaker located in the hypothalamic suprachiasmatic nuclei (SCN), and this pacemaker controls and coordinates circadian rhythms [1,2]. The alerting effects of short-wavelength light are induced by counteracting both the circadian and homeostatic drives for sleep, while during the day only the homeostatic sleep pressure is affected [19]
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