# The Calculated Circadian Effects of Light Exposure from Commuting
## 2 Materials and Methods  
### Light Exposure Measurements  
A calibrated Everfine SPIC-300 spectral irradiance meter was used to measure the illuminance and SID. The sensor of the spectral irradiance meter can be separated from the rest of the instrument, which it communicates with via Bluetooth. In order to estimate the corneal illuminance and SID while traveling safely, the sensor was mounted on a modified helmet. When the operator wore the helmet to conduct the measurements, the sensor was, therefore, in the center of the operator's forehead, just above the eyes (Figure 1). After initiating the instrument, the equipment recorded the first measurement and automatically measured the subsequent light. The time taken for each measurement varied. The average measurement frequency during the trips was 1.4 recordings per minute. The measurements ceased when the operator manually stopped the equipment. A series of measurements were automatically and continuously recorded while the operator traveled. The mounting position of the sensor on a helmet was used to ensure the safety of the operator. However, comparisons were made between the measurements of the light striking the sensor when mounted on the helmet and when placed in front of the cornea, and very little difference was found. The same instrument was used for this comparison, with the same operator (Figure 1). The operator stood outdoors, measured the light once when the sensor was on the helmet, and then immediately moved the sensor onto her right eye and recorded another measurement. This process was repeated three times. The percentage difference of the measured irradiance was calculated as the difference between the irradiance at the helmet position and the irradiance at the eye position divided by the irradiance at the eye. The three percentages were 1.2%, \(-\)0.5% and 1.3%, which are all less than the measurement uncertainty of the instrument. Measurements were obtained for a total of 21 trips, representative of those undertaken by the commuters. All trips were taken in the summer and autumn (from December 2019  
Figure 1: Photo of the operator wearing the modified helmet with the sensor attached on it. to March 2020) in the Sydney metropolitan region in Australia. Seven trips were taken for each commuting mode: driving, riding trains, and walking. Additionally, all trips were taken during the morning peak hours (within the time range of 07:30 to 10:00). For driving, the average starting time was 08:54 a.m. and the average ending time was 09:22 a.m. For riding trains, the average starting time was 08:38 a.m. and the average ending time was 08:59 a.m. For walking, the average starting time was 08:28 a.m. and the average ending time was 09:00 a.m. The duration of the trips varied from 12 min to 41 min. The average duration of all trips was 27 min. For driving and walking, the direction of travel included all four directions (north, south, west, and east, approximately) for each mode of commuting. For train rides, the trips include one railway line which is a loop, as well as three other railway lines, for which measurements were collected in both directions of travel. All the measurements were conducted by the same operator (Figure 1). When driving, the operator wore the modified helmet with the attached sensor and initiated the spectral irradiance meter before she started to drive. The equipment automatically recorded the measurements as she drove. The primary light source was the daylight coming through the front windshield and the windows of the vehicle. The operator was free to perform any necessary movements for safe driving, such as checking the GPS, adjusting the side-view mirrors, monitoring traffic conditions, etc. The seven trips that were taken for the driving mode started at different locations and ended at different destinations. The measurements were conducted inside of the same vehicle (model: 2018 Toyota, CH-R) with tinted side windows.