Data analysis
visual complaints, ’
For descriptive analyses, mean (M) and standard deviation (SD) were calculated. All graphs and descriptive ANOVA results show means and 95% confidence intervals (CI) of means unless otherwise noted.For statistical testing of the hypotheses, two-factor r-ANOVAs were performed with the factor ‘light intervention’ (2 levels: stronger light pulse, weaker light pulse) and the time-of-day factor ‘test cycle’ (5 levels: test cycle 1–5) for each of the three parts (‘baseline’, ‘intervention’, and ‘different light’) of the aPVT reaction speed and GNT reaction speed, the PANAS positive and negative affect scale, and the NASA TLX. For VAS, a three-factor r-ANOVA was performed (factors: ‘pre-/post aPVT measurement’; ‘light intervention’ and ‘test cycle’). Before performing all analyses of variance, data were checked for outliers, normality, and sphericity, and in case of violation of sphericity, a Greenhouse–Geisser correction of the significance level was applied. All pairwise post hoc comparisons were performed with Bonferroni-corrected significance levels. To avoid a possible error caused by the application of three r-ANOVAs separately for each 5-min period of the aPVT, a full three-factorial r-ANOVA model with the factors ‘light intervention’, ‘test cycle’ and ‘parts’ was also run for aPVT reaction speed. This analysis confirmed the results of the three separate two-factor r-ANOVAs and is reported in Supplementary Materials Data of lapses in the aPVT and commission errors in the GNT violated the assumption for applying r-ANOVAs. Therefore, non-parametric Friedman ANOVAs were first run separately for each intervention to identify potential effects of the test cycle. If the Friedman ANOVA indicated a significant effect, pairwise Wilcoxon tests with Bonferroni-corrected significance levels were then calculated. Furthermore, for each test cycle, differences between the two interventions were calculated by applying Wilcoxon tests with Bonferroni-corrected significance levels for multiple comparisons (alpha = 0.01).Individual HRV data had to fulfill a quality criterium (delivered by the software ‘Cardioscope Analytics’) to be included in the statistical analyses. If the quality fell below 95%, the HRV data were replaced with the last observation of the subject carried forward. Data replacement was required for 5.0% of all recordings for the aPVT and for 6.4% for the GNT. HRV data were analyzed for the three parts (‘baseline’, ‘intervention’, and ‘different light’) of the aPVT and the entire 10-min period of the GNT. To control for possible carry-over effects of the light interventions, HRV data for the five 25-min resting periods were also analyzed.The effects of the intervention on perceived visual complaints, FrACT, and subjective sleep quality were determined by t-tests for two dependent samples.A confounder analysis was performed on physiological states during resting periods. We also compared reaction speeds in the two attention tasks between the first and second study day. The results are presented in Supplementary Materials All data analyses were performed using the software SPSS (IBM SPSS Statistics for Windows, version 28.0) with a 5% significance level and two-sided testing. Effect sizes in r-ANOVAs are shown as partial eta-squared values (η