30 minutes of intervention every day for 14 consecutive days.

30 minutes of intervention every day for 14 consecutive days.

30 minutes of intervention every day for 14 consecutive days.

During intervention, the participants close their eyes and wear an eye mask and stereo earphones. They then listen to 30 minutes of 10 Hz BBT music (intercalated with relaxing music) through their mobile phone. The intervention music was first embedded in the participant's mobile phone and the BBT music application was purchased from the mobile phone app (Brainwave Studio software, Dalcoms Inc). When listening to music, 10 Hz light stimulation was added to the BBT and FL group (using a mobile phone). Table 1 shows the intervention status. The rhythmical photic stimulation program was a commercially available mobile phone app (Strobe Therapy software released by FuwhatSoft).

There were 21 questions in the BDI, and a self-rated method was used for participants to fill in their thoughts in the last 2 weeks. A 4-point Likert scale was used. The score range of each question was 0-3 points. A total score of 0-12 points was normal, 14-19 points was mild depression, 20-28 points was moderate depression, and 29-63 points was severe depression.

There were 18 questions in the PSQI, and participants used a self-rated method to fill in their sleep quality in the last month on a 4-point Likert scale. The total score range was 0-21 points. The higher the score, the poorer the sleep quality. This scale has seven dimensions, including: (1) Subjective sleep quality; (2) Sleep latency; (3) Sleep duration; (4) Sleep efficiency; (5) Sleep disturbances; (6) Daytime dysfunction; and (7) Use of sleep medication. PSQI had good validity and reliability(Tsai et al., 2005).

HRV was used to measure heart rate variability, including five markers: (1) Mean heart rate; (2) SDNN: Standard deviation of all RR intervals, represent the physiological health of autonomic nervous system; the higher the SDNN, the better the physiological health of the autonomic nervous system; (3) nLF: Normalized low frequency, reflects sympathetic nervous activity. The higher the value, the greater the activity; (4) nHF: Normalized high frequency, reflects parasympathetic nervous activity. The higher the value, the greater the activity; (5) LF/HF, a marker reflecting sympathetic and parasympathetic nervous activity.

The vitality (VT) and mental health scales (MH) in SF-36 were used for measurement of secondary outcomes The SF-36 scale covers eight dimensions and 36 questions. Each dimension can be used for testing separately and has good validity and reliability (Yang et al., 2018). The VT and MH scales have four and five questions, respectively. A 6-point Likert scale is used. The score of each question ranges from 1 to 6 points and the total score of the VT and MH scales are 4-24 and 5-30 points, respectively. A higher score indicates better vitality or mental health.