Table 2.

Studies of short-term HRV measurement with color as the experimental stimulus.

Authors	Experimental Variables	Number of Participants	Data Analysis Method	HRV Measurement	HRV Parameters that Changed Significantly	Study Limitations
Chäfer and Kratky [28]	Color lighting (red, green, blue; 700 lux)	n = 12 (average 29.9 years old)	T-test	NN, SDNN, RMSSD, VLF, LF, HF, LF/HF, DFA	VLF, HF, DFA	The study focused primarily on color light therapy; thus, the color light of high illuminance was used for the experiment.
Choi et al. [29]	Color lighting (blue, red, white)	n = 92 (56 men and 36 women; average 26.4 years old)	T-test, ANOVA	HF, LF, LF/HF, SDNN, RMSSD	HF, RMSSD	The experiment was conducted in color light of low illuminance not used in daily life. The color lighting was evaluated after the measurement of HRV.
Litscher et al. [30]	Color lighting (red, blue; 140 lux)	n = 7 (2 men and 5 women/average 34.1 years old)	T-test, ANOVA	HR, total HRV, LF/HF	HR, total HRV	In this pilot experiment, nasal temperature, heart rate, and HRV were measured.
Yuda et al. [31]	Color lighting (red, green, blue)	Experiment 1: n = 12 (10 men and 2 women; average 23 years old) Experiment 2: n = 4 (2 men and 2 women; average 23 years old)	T-test, ANOVA	LF, HF, LF/HF	HF, LF/HF	On the basis of the result from Experiment 1, in Experiment 2, HRV measurement was performed to verify that HF decreased in blue light.
Araujo et al. [32]	Color lighting (red, blue; 22–30 lux)	n = 5 (22–52 years old)	Shapiro test ANOVA	HR, RR, SDNN, RMSSD, LF, HF, LF/HF, SD1, SD2, ApEn, SampEN	HF, ApEn	HRV was measured in color lighting of low illuminance; it was found that photoplethysmography could measure HRV reliably.