The Influence of Colored Light on Heart Rate Variability and Human Discomfort

Purpose: This study examined changes and relationships between perceived discomfort states and heart rate variability (HRV) during exposure to colored lights. Methods: Twenty university students, equipped with a digital Holter recorder, were exposed to white, blue and red lights for 10 min, respectively, with a 5-min interval among these stimuli. HRV series were recorded at rest within each lighting period, and time and frequency domain HRV parameters were analyzed. A visual analog scale assessed discomfort states throughout the experiment. Results: Significant increases were found during exposure to the red light in both the low-to-high frequency ratio (LF/HF, p<0.05) and low frequency (LF, p<0.05), accounting for a heightened activity of the sympathetic system. Blue light stimulation did not induce the same effects in frequency components. Both LF and the LF/HF ratio decreased under blue light condition, whereas high frequency (HF) increased, showing more cardiac relaxation. Compared with red light, blue light improved the subjective measures of discomfort scores. Conclusions: Red light exposure during daytime enhances autonomic arousal, suggesting alterations in sympathovagal balance. The moderate increase in vagal-related frequency components due to increased parasympathetic activity is associated with blue light exposure, which may be less stressful than the red one. Perceived discomfort levels correlated with HRV. Although the influence of light on psychological and physiological processes is not fully clarified, the results suggest significant associations between exposure to different colored lights, physiological reactivity and mood, which could be used in the design of lighting interventions both in real-life conditions (e.g., workplace) and in clinical applications.