Reactivity of heart rate variability after exposure to colored lights in healthy adults with symptoms of anxiety and depression

Studies on human psychological domains associated with color specific light effects have been reported. The heart rate variability (HRV) has been suggested to be a useful tool for the detection of short-term effects of light on the autonomic nervous system (ANS). The emotional state of an individual has an independent effect on the HRV. The purpose of this study was to investigate the acute HRV reactivity after illumination with colored lights and determine the possible interaction between the colored lights and emotional states. Ninety-two healthy adult volunteers underwent short-term measurement of HRV before and after exposures to blue (λmax 420, 380-495nm, 0.04lux, 0.41μW/cm²), red (λmax 765nm, 620-780nm, 0.4lux, 1.62μW/cm²) and white (49.5lux, 12.9μW/cm²) colored fluorescent lights for 5 min during the daytime. A depressed group and an anxious group were identified in 28 (30.4%) and 23 (25.0%) of the subjects, respectively, according to their responses to the Korean version of the hospital anxiety and depression scale (score≥8). The high frequency (HF) reactivity and the root mean square successive differences (RMSSD) were significantly different in the depressed (p<.05) and anxious groups (p<.05) based on the colored lights. The parasympathetic activity was decreased with red light in the depressed and anxious groups; this activity was further decreased in subjects with both symptoms. However, it was unchanged in the subjects without symptoms of depression and anxiety. The results of this study showed that the emotional state of the subjects was an important modulator of the acute effects of dim colored light on the ANS.