The investigation of the effect of various colored light on human autonomic nervous system and its relationship with personality traits

LED light sources are becoming more and more common for everyday use both as lighting and decorative purposes taking a number of advantages compared to traditional light sources. For this reason, the psychological and physiological reactions taking place in people exposed to colored lights has been aroused curiosity and become subject to an increasing number of researches. Some of the current researches indicate that red and blue light have a number of effects on human autonomic nervous system, while others suggest that no significant effect is seen. These contradictory results can be attributed to not taking into consideration the fact that color preference and perception are closely in association with people's personality traits. In this context, in this thesis, it is aimed to investigate that the effects of white, red and blue LED lights on the autonomic responses such as heart rate, heart rate variability, electrodermal activity; and alterations of perception such as emotional state, time, and spaciousness perceptions in humans with different personality traits. In accordance with this purpose, a total of 48 subjects (15 female, 33 male) aged between 19 and 43 (28 ± 6) were included in the study. The personality traits of the subjects were determined by the Big Five Personality Traits. The subjects were exposed to 3 different colors of light (white, red and blue). All subjects were exposured to each colored light for 8 minutes at an intensity of 300 lux illumination. During exposure, electrodermal activity and heart rate values of the subjects were recorded and in this manner heart rate variability values were calculated using heart rate values. After each light exposure, the subjects were asked to fill Self Assessment Manikin Test in order to determine their instant emotional state and to answer the personal perception questions to determine the instant time and spaciousness perception. With the aim of analyzing data, One-way ANOVA, Spearman Row Differences Correlation Test and Multiple Regression Analysis (stepwise) were used. As to our results, it was determined that the mean values of electrodermal activity measured in red and blue light exposure was significantly higher than those measured under white light (p <0,01). It was found that red and blue light had no significant effect on heart rate and heart rate variability values (p> 0.05). However, investigating the predictiveness between personality traits and heart rate variability parameters, agreeableness scores were found to be negatively predictive of LF/HF ratio during exposure to red (p<0,01) and white light (p<0,05). On the other hand, investigating the pleasure, arousal and dominance levels under each light exposure, it was concluded that pleasure level during blue and white light exposure and the arousal and dominance levels during red light were significantly higher (p<0,05). In addition, it has been found that the time flow during red light exposure was found to be significantly slower (p<0,01) and spaciousness perception during red light exposure was found to be significantly narrower (p<0,01) compared to white and blue light. Agreeableness scores were found to be positively predictive of pleasure level during red light and openness to experience scored were found to be negatively predictive of spaciousness perception during red light exposure. Consequently, red light disturbs the perception of time flow and spaciousness; and increases the level of arousal that changes due to sympathetic nervous system activity. Agreeableness and openness to experience traits change the sympathovagal balance during red and white light exposure in favor of the parasympathetic system.