BRILLIANCE · Bright light effect on performance and alertness during daytime

Final Activity Report Summary - BRILLIANCE (Bright light effect on performance and alertness during daytime)

It has been shown that bright light could affect the human central nervous system either: 1. through the circadian, i.e. body, clock system to cause phase shifts or 2. independent of the body clock, through the alerting effect. Existing research concentrates mainly on the effects of night time exposure to bright light (BL) on the circadian rhythms of physiological variables. Little is known about BL effects on cognitive performance and alertness during daytime. Many studies have shown decreased performance and alertness in the afternoon hours, commonly called the ‘post-lunch dip’. It has been hypothesised that there is a relationship between the post-lunch dip and the 12 hr rhythm, namely the ultradian, of sleepiness. Post-lunch dip manifests itself in real life in terms of decreased productivity and increased accident rates. Hence, the application of an appropriate regime of BL exposures could be directed at alleviating these effects. The aim of the project was to address a number of research questions, such as the following: 1.whether a regime of intermittent bright light exposure could affect daily rhythms in processing of laterally presented stimuli. 2. whether a regime of intermittent bright light exposure could affect alertness and affective state. 3. how did participants perceive both lower light and bright light conditions. The participants were 20 student volunteers, 15 female and 5 male, between 19 and 24 years of age. Pre-study screening was undertaken to ensure that participants had a normal sleep-wake cycle and were free from medical and psychiatric disorders. All participants maintained regular eight hour sleep schedules for two weeks before the experiment. Each participant took part in one light condition session counterbalanced by another light condition session two weeks later. There were altogether eight experimental sessions that lasted 13 h, from 07.30 to 20.30. Participants’ performance, mood and light perception were measured by both paper and pencil and computer-based tasks and questionnaires. Performance and mood were measured 13 times at 30 minute intervals starting from 08.00. Light perception was registered for the entire session at the end of each experimental session. Experimental conditions, such as noise, humidity, ambient temperature of 20° C and light, were controlled in order to minimise influences on performance and mood. No significant main effect of intermittent bright light (IBL) on the daily trends of speed and accuracy of processing of laterally exposed stimuli was found. However, significant interaction effects between visual field and time of measurement on accuracy of spatial and verbal stimuli processing, i.e. performance, were observed. Asymmetric and ultradian differences in hemispheric information processing were evident, supporting earlier findings. The, close to statistically significant, effects of BL exposure on performance that were found in this study supported this reasoning to some extent, i.e. the main effect of light conditions on speed of verbal and logical task performance, the interactive effect of light conditions and measurement time on daily oscillations in speed of information processing on spatial tasks, and the interactive effect of bright light and measurement time on global vigour assessment. The undertaken assessment of light conditions showed that even the intermittent BL levels which were applied in this study were reported by the participants to be less comfortable, more glaring and less natural than the ordinary room light conditions which might have affected their responding. It seemed that a more practical solution would be a longer lasting application of lower intensity BL than the one used in the experiment. For example, it was shown in Swedish studies that such a procedure was effective in performance and mood improvement and might be experienced as being more comfortable by the participants. IBL appeared to affect daily rhythms in global vigour which was consistent with other research findings showing moderate effects of daytime BL exposure on alertness. Given the present findings, this observation had implications for the application of bright light in real life work situations.

Data: CORDIS, © European Union