Effects of illuminance and correlated color temperature of indoor light on vitality, mood and performance

Background and Objective: The empirical evidence has endorsed that, in addition to enabling visibility, light stimulates brain responses, which impact physiological, psychological, and neurobehavioral human functions, such as vigilance, mood, vitality, and cognitive performance known as the non-visual or non-image-forming (NIF) effects of light. This investigation was conducted to examine the NIF effect of the illumination levels and correlated color temperature (CCT) on vitality, mood, and cognitive performance during the midafternoon hours.Materials and Methods: In this study, twenty-five healthy adults were tested in a balanced, designed experiment. At first, a simulation of an office environment with a heating and air conditioning system and equipped with an adjustable lighting system at ۳۰۰ and ۵۰۰ lux illuminance level was designed. In the present study, lighting conditions included dim light condition ( <۵ lux), and correlated color temperatures (CCT) of ۲۷۰۰ K, ۴۰۰۰ K, ۸۰۰۰ K, and ۱۲۰۰۰ K at illumination levels of ۳۰۰ and ۵۰۰ lux were investigated. The vitality and mood scales and cognitive performance tests for measuring work memory (n-back), inhibitory capacity (GO/NO-GO), psychomotor vigilance task (PVT), selective attention and divided attention were used to obtaining the needed data. Also, participants completed questions about the subjective state of their evaluation of the lighting condition and the environment at the end of each session. Data were analyzed using repeated-measures analyses of variance (ANOVA). Two-tailed paired Student’s t-tests with Bonferroni correction (when appropriate) were applied for additional comparisons. The data were analyzed using version ۲۲.۰ of the SPSS software (IBM, Armonk, NY, USA) and a p-value < ۰.۰۵ was considered statistically significant.Results: The results revealed that in illumination levels of ۳۰۰ and ۵۰۰ lux, CCT of ۸۰۰۰ K and ۱۲۰۰۰ K, enhanced normalized vitality and mood and decreased normalized response time in the PVT, GO/NO-GO and selective attention tests compared with dim light conditions. Based on the findings, there were no significant differences between the CCT of ۲۷۰۰ K, ۸۰۰۰ K, ۱۲۰۰۰ K, and ۴۰۰۰ K in the normalized mood and vitality scores and normalized reaction time and numbers of errors in the cognitive performance tests that used for measuring thesustained attention, working memory, inhibitor capacity, selective attention, and divided attention in the two illumination levels of ۳۰۰ and ۵۰۰ lux. Nevertheless, the results trend exhibited a more positive ۵۰۰ lux illumination level on the measured variables. But it did not reach a statistically significant level. The results indicate that the participants preferred more light with an intensity of ۵۰۰ lux compared to ۳۰۰ lux at different color temperatures.Conclusion: The present study, in line with previous studies, provides further evidence on the positive effect of lighting parameters such as correlated color temperature andillumination level on physiological and neurophysiological human functions. Therefore, it is suggested that the design and use of lighting interventions can be used as an auxiliary approach along with other interventions to improve the level of mood, vitality, and cognitive performance.

کلیدواژه ها:

Light ، Correlated color temperatures ، Performance