Moral decision-making at night and the impact of night work with blue-enriched white light or warm white light: a counterbalanced crossover study

Abstract

Background

Cognitive function, including moral decision-making abilities, can be impaired by sleep loss. Blue-enriched light interventions have been shown to ameliorate cognitive impairment during night work. This study investigated whether the quality of moral decision-making during simulated night work differed for night work in blue-enriched white light, compared to warm white light.

Methods

Using a counterbalanced crossover design, three consecutive night shifts were performed in blue-enriched white light (7000 K) and warm white light (2500 K) provided by ceiling-mounted LED luminaires (photopic illuminance: ∼200 lx). At 03:30 h on the second shift (i.e. twice) and at daytime (rested), the Defining Issues Test-2, assessing the activation of cognitive schemas depicting different levels of cognitive moral development, was administered. Data from 30 (10 males, average age 23.3 ± 2.9 years) participants were analysed using linear mixed-effects models.

Results

Activation of the post-conventional schema (P-score), that is, the most mature moral level, was significantly lower for night work in warm white light (EMM; estimated marginal mean = 44.3, 95% CI = 38.9–49.6; p^holm=.007), but not blue-enriched white light (EMM = 47.5, 95% CI = 42.2–52.8), compared to daytime (EMM = 51.2, 95% CI = 45.9–56.5). Also, the P-score was reduced for night work overall (EMM = 45.9, 95% CI = 41.1–50.8; p=.008), that is, irrespective of light condition, compared to daytime. Neither activation of the maintaining norms schema (MN-score), that is, moderately developed moral level, nor activation of the personal interest schema (i.e. the lowest moral level) differed significantly between light conditions. The MN-score was however increased for night work overall (EMM = 26.8, 95% CI = 23.1–30.5; p=.033) compared to daytime (EMM = 23.1, 95% CI = 18.9–27.2).

Conclusion

The results indicate that moral decisions during simulated night work in warm white light, but not blue-enriched white light, become less mature and principle-oriented, and more rule-based compared to daytime, hence blue-enriched white light may function as a moderator. Further studies are needed, and the findings should be tentatively considered.

Trial registration: ClinicalTrials.gov (ID: NCT03203538) Registered: 26/06/2017; https://clinicaltrials.gov/study/NCT03203538

KEY MESSAGES

• The quality of moral decision-making, seen as the activation of cognitive schemas depicting different levels of moral development, was reduced during simulated night work in warm white light, but not blue-enriched light, compared to daytime.

• The quality of moral decision-making sems to be reduced during simulated night work, compared to daytime.

• More studies assessing the impact of night work and light interventions on the quality of moral decision-making are needed to validate these tentative findings.

Keywords:

• Shift work
• sleep deprivation
• colour temperature
• light emitting diode

Acknowledgements

The authors gratefully acknowledge the assistance of Jelena Mrdalj, Eirunn Thun, and Torhild T. Pedersen with data acquisition. We also thank all participants in the study.

Author contributions

Conception and design: ES, AH, OKO, and SP. Data acquisition: ES. Data processing: OKO. Data analysis: ES. Interpretation of results: ES, AH, OKO and SP. Drafting of the paper: ES. Critical revision of the paper for intellectual content: ES, AH, OKO, and SP. All authors approved the final version of the paper and agreed to be accountable for all aspects of this work.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

Data from this study are available from the corresponding author upon reasonable request.

Additional information

Funding

This work was supported by two PhD positions funded by the Faculty of Psychology, University of Bergen, Norway. Sunde is currently in a postdoctoral position funded by the Norwegian Research Council under Grant number 303671. The study was conducted in the laboratory facilities at the Faculty of Psychology, University of Bergen, Norway. The LED luminaires were provided free of charge by Glamox AS, BU Norge. Glamox AS had no role in the study design, data collection, analyses and interpretation, manuscript preparation, or publication decision.