# Physiological Study of Visual and Non-Visual Effects of Light Exposure
## 3 Experiment on Visual and Non-Visual Effects of Light Exposure  
### Methods  
The participants were 21 undergraduate and graduate students in their 20s (20 males and 1 female, mean age = 22.0, SD = 0.93). We removed the data for one participant due to a measurement problem (the adhesive failure of a probe) and analyzed the data for 20 participants (19 males and 1 female, mean age = 22.1, SD = 0.92). The number of the participants was chosen to be equal to or more than those of conventional studies [4; 7; 11; 12; 14]. The Ishihara color vision test chart [7; 34] was used to verify the absence of color blindness. In addition, the Edinburgh dominant hand experiment [35] was used to confirm that the participants were right-hand dominant. To verify that the participants had similar habits, we confirmed that they did not smoke, had not taken any medications within 2 weeks, had not traveled to a location with a time difference within 3 months, had not worked night shifts, and had slept 7-8 h on a habitual schedule for 1 week before the experiment [7; 8; 9; 36]. The participants were instructed not to eat for 2 h prior to the experiment and not to consume alcohol, caffeine, or supplements for 12 h prior to the experiment as these can affect physiological responses [6; 7; 11]. Before the experiment, we explained the purpose and method of the experiment and related safety issues. Then, each participant provided informed consent. After the experiment, each participant was paid JPY 1050 per hour for their time. We used red and blue light with visual and non-visual effects that have been confirmed to be contrastive in conventional studies [2; 4; 5; 14; 16] and white light as a control condition. The illumination conditions were selected based on six lighting characteristics that caused non-visual effects in previous studies:  
1. Spectrum: According to a previous study [37] that investigated the spectral power of monochromatic blue light and the percentage of change in the suppression of melatonin secretion, the spectrum must have a short-wavelength component of at least 20 \(\mu W/\mathrm{cm}^{2}\) to produce non-visual effects. In contrast, this study employed blue, red, and white (baseline condition) light. The light color spectra had to be difficult toperceive but sufficient to produce the visual effects. Spectra were measured with a C-7000 spectrometer (SECONIC, Tokyo, Japan) (Figure A1);
2. Illuminance: Illuminance had to be sufficiently high to affect arousal level but low enough not to induce a perceivable change in light color. According to a previous study [36] investigating the relationship between illuminance and arousal level (subjective arousal level using the percentage of suppressed melatonin secretion), the arousal level increased at around 70 lx (illuminance at the cornea) and reached an intermediate arousal level at 90-180 lx. Therefore, we set the illuminance to 90 lx at the corneal position;
3. Irradiation time period: The irradiation time period was set based on the following: (i) participants' sleep habits; (ii) under appropriate lighting conditions, non-visual effects during the daytime may affect arousal level, performance, etc. ; and (iii) irradiating light with a large short-wavelength component at night may lead to sleep disorders [38]. In this study, the irradiation time period was set as 10:00 to 17:00;
4. Irradiation duration: Previous studies [6,16] indicated that non-visual effects could be observed after 12 min of irradiation. Additionally, the effect on arousal level was independent of the length of irradiation time if it was longer than 12 min. Therefore, we set the irradiation duration to 20 min in consideration of fatigue and to ensure a sufficient irradiation time for the onset of the non-visual effects;
5. Spatial distribution: Previous studies [39, 40, 41] revealed that non-visual effects depend on the retinal area irradiated by light.