Abrupt light transitions in illuminance and correlated colour temperature result in different temporal dynamics and interindividual variability for sensation, comfort and alertness

Abstract

Detailed insights in both visual effects of light and effects beyond vision due to manipulations in illuminance and correlated color temperature (CCT) are needed to optimize study protocols as well as to design light scenarios for practical applications. This study investigated temporal dynamics and interindividual variability in subjective evaluations of sensation, comfort and mood as well as subjective and objective measures of alertness, arousal and thermoregulation following abrupt transitions in illuminance and CCT in a mild cold environment. The results revealed that effects could be uniquely attributed to changes in illuminance or CCT. No interaction effects of illuminance and CCT were found for any of these markers. Responses to the abrupt transitions in illuminance and CCT always occurred immediately and exclusively amongst the subjective measures. Most of these responses diminished over time within the 45-minute light manipulation. In this period, no responses were found for objective measures of vigilance, arousal or thermoregulation. Significant interindividual variability occurred only in the visual comfort evaluation in response to changes in the intensity of the light. The results indicate that the design of dynamic light scenarios aimed to enhance human alertness and vitality requires tailoring to the individual to create visually comfortable environments.

Alerting Effect of Light: A Review of Daytime Studies

“…In another study, Kompier et al [48] found an immediate increase in subjective alertness when the subjects were exposed to 45 minutes of 1000 lx in comparison to 100 lx. The effect was temporary and lasted approximately 20 minutes.…”

“…Whether the alerting effect of monochromatic light is noteworthy in comparison to control conditions with higher illuminances remains to be determined. Based on the results of the summary seven out of twenty studies concluded that light definitively enhances alertness by increasing performance or subjective indicators (illuminance-based studies: [47,48,44,53]; CCT-based studies: [56,45,57]). Table 7 shows the studies that recorded an alerting effect of light (beyond only the physiological effect).…”

“…In another study, Kompier et al [48] concluded that an increase in subjective vitality and decrease in subjective sleepiness were attributed to the increase of illuminance and not CCT. They found the alerting effect to be immediate, as it lasted for at least 20 minutes and did not exceed the duration of the exposure.…”

Objective Measures of Immediate “Energizing” Effect of Light: Studies Review and Data Analysis

“…The measurement of skin conductance on the hand, or electrodermal activity (EDA), was reported in five articles of the same investigative group [ 55 , 56 , 63 , 65 , 66 ] ( Table 1 ). Only one of these studies revealed a differential effect of light—brighter light increased skin conductance, which evidenced greater sympathetic tone in the test subjects.…”

Testing a Single-Case Experimental Design to Study Dynamic Light Exposure in People with Dementia Living at Home

“…The illuminance and spectral composition of natural light are additionally influenced by weather conditions, such as haze and overcast [13,14]. In addition, there are indications that, depending on the time of day and the individual's affective and/or mental state, different lighting conditions across the day are needed to optimally support human functioning [15,16]. Particularly for persons who have older eyes, a diminished functioning of the internal clock, and who receive little direct exposure to daylight, dynamic artificial lighting that mimics the natural rhythm of night and day may stimulate physical and mental health and generate a positive experience.…”