Time-Dependent Effects of Altered Prebedtime Light Exposure in Enclosed Spaces on Sleep Performance Associated with Human States

Abstract

Purpose: Exposure to artificial light influences human performance, which is essential for maintaining healthy work and sleep. However, existing research has not explored the intrinsic links between sleep performance and human states over time under prebedtime light exposure interventions (LEIs).

Methods: To investigate the time-dependent effects of altered prebedtime light exposure, four LEI groupings (#L1 - #L4) and a Time factor (D8, D9, and D10) were chosen for sleep experiments in enclosed spaces. Forty-eight young adults recruited were available for data analysis. Subjective alertness (SA), negative affect (NA), subjective sleep, and objective sleep were measured via the Karolinska Sleepiness Scale, Positive and Negative Affect Schedule, Next-day Self-assessment Sleep Quality, and joint assessment of wrist actigraphy and sleep diaries, respectively. Statistical analysis was used for the effects of light exposure on the human states (corresponding to the SA and NA) and sleep performance, while the process model helped construct the associations between the two.

Results: The statistical effects revealed that the Time had a significant main effect on subjective sleep and changes in prebedtime alertness; the LEI had a significant main effect only on sleep onset latency (SOL). After undergoing altered prebedtime light exposure, the mean SA increased at prebedtime of D9 (p = 0.022) and D10 (p = 0.044); No significant effect on the NA was observed; Mean subjective sleep had a significant increase from D8 to D10. Moreover, five actigraphy-estimated sleep parameters were interrelated. In light of this, a chained pathway relationship was identified. The SOL played a mediating predictor between prebedtime state and objective sleep, which was linked to the awakening state through subjective sleep.

Conclusion: Our study suggests that time-dependent effects of altered prebedtime light exposure on sleep performance are associated with human states at prebedtime and awakening, with implications for its prediction of sleep health.

Keywords: alertness; negative affect; non-visual effects; prebedtime light exposure; sleep onset latency; sleep performance.

Figure 1

Spectrum power distribution measured at eye level for one baseline (300 lx, 4000 K) and four light exposure intervention settings.

Figure 2

Experimental setting and scenes display via a 2-D graph of the whole experimental layout. (a) is a simulated sleep chamber equipped with a single bed, “3 × Sleep chamber” means that three identical sleep chambers are offered to 3 participants simultaneously; (b) is a simulated workspace with three seats and six LED round lamps in an enclosed space, where reading tasks are performed; (c) is a control area with a computer.

Figure 3

Flowchart of information on enrolled participants.

Figure 4

Study procedure and protocol design.

Figure 5

Methodology and process of data processing and analysis.

Figure 6

Mean of subjective alertness for (a) t1 and t2 at prebedtime, (b) t3 and t4 at awakening.

Figure 7

Estimated marginal means of the changes in subjective alertness: (a) before bedtime, (b) after waking up, and the changes in negative affect: (c) before bedtime, (d) after waking up. Error bars represent 95% confidence intervals. #L1 - #L4 indicate groupings from baseline to intervention distinguished by LEI. Significant is marked, *p < 0.05.

Figure 8

Mean of negative affect for (a) t1 and t2 at prebedtime, (b) t3 and t4 at awakening.

Figure 9

Estimated marginal means of (a) PSA, perceived sleep adequacy, and (b) PSQ, perceived sleep quality. Error bars represent 95% confidence intervals. #L1 - #L4 indicate groupings from baseline to intervention distinguished by LEI. Significant is marked, * p < 0.05.

Figure 10

Estimated marginal means of sleep parameters: (a) TST, total sleep time; (b) SOL, sleep onset latency; (c) WASO, wake after sleep onset; (d) SE, sleep efficiency; and (e) SFI, sleep fragmentation index. Error bars represent 95% confidence intervals. #L1 - #L4 indicate groupings from baseline to intervention distinguished by LEI. Significant is marked, *p < 0.05.

Figure 11

Results for standardized path analysis with a process model. Rectangles denote the latent variable, of which directed lines represent the value of path coefficients (p value).