Methods
All participants in this study were recruited from the staff of Changsha Aier Eye Hospital. Patients or the public WERE NOT involved in the design, or conduct, or reporting, or dissemination plans of our research.
Two commercial devices were used in the study. The HOBO, a commonly suspended light metre placed in front of the chest, was used to record the light intensity in lumens per square foot (lum/ft²) at a frequency of one measurement per minute.9 On the other hand, the Clouclip, which is equipped with a light sensor and attached to the right arm of the eyeglasses, recorded the light intensity in lux at a frequency of one measurement every 2 min. Detailed specification and validation tests have been reported previously.12
Initially, we conducted an experiment to determine if there were any disparities in the measurements of light intensity between the HOBO and Clouclip, as well as between the two HOBO devices. To achieve this, we initially placed the Clouclip and one HOBO in 26 different light environments ranging from 100 to 26 242 lux. Subsequently, we placed the two HOBO devices in the same 26 light environments. For each light environment, we performed five measurements using each device. Subsequently, we calculated the average value of the five readings for comparison purposes.
After confirming the measurement discrepancy between the two devices, all participants were requested to wear two HOBOs and one Clouclip simultaneously for the duration of 1 day (figure 1). This measurement was taken to collect data regarding the light intensity exposure on the wrist, chest and eye positions. Specifically, a HOBO device was affixed to the dorsal side of the left wrist using a custom-made elastic strap, at the same position as a traditional wristwatch. For participants wearing full sleeves, we asked that the elastic strap to be tied over the sleeves. Participants were instructed to regularly monitor the positioning of the HOBO every 10 min, ensuring it remained consistently placed on the back of the hand with its light sensor facing outward. Furthermore, participants were required to ensure that their entire bodies remained in the homogeneous ambient light environment. For example, participants were not permitted to extend their wrists outside a window while indoors. Following the experiment, we employed a simple questionnaire to inquire whether the participants had conducted regular checks in accordance with our guidelines. Additionally, we will analyse the collected data. For instance, if the data indicate that a subject has been in a very dim environment for an extended period, we will investigate and verify this through phone communication. The other HOBO was pinned to the coat to ensure that the light sensor was constantly facing outward. Additionally, a Clouclip was attached to the right arm of the participants’ spectacles. For those who did not wear spectacles, frames without lenses were provided, so that the Clouclip could be worn. The data were collected from 22 April 2020 to 15 July 2020, which included 10 rainy days, 13 cloudy days and 6 sunny days. The variety of weather conditions provided a considerable range of light scenarios for testing. During the wearing period, participants were encouraged to wear the Clouclip throughout the day, excluding bathing and sleeping times. They were also encouraged to continue with their habitual activities as usual. HOBO and Clouclip were set to start and end the data collection at the same time. Both the HOBO and Clouclip devices were set to initiate and conclude the data collection simultaneously.
Figure 1(A) Location of the sensors in Clouclip. (B) Location of the sensors in HOBO. (C) One participant who wore a HOBO on the left wrist, a HOBO on the coat and a Clouclip on the right arm of spectacle.
Data processing and statistical analysis
Once the participants completed the 1-day wear of the devices, the light intensity values measured by the HOBO and Clouclip were downloaded as Excel files for each individual participant. Due to the difference in units between the two devices, we performed a unit conversion to make the data comparable by using the equation 1 lum/ft²=10.76 lux. Additionally, there was a disparity in the frequency of data collection between the HOBO and Clouclip. To align the data collected by both devices, we calculated the average of the HOBO data at 2-minute intervals. Afterwards, we determined the effective wearing time of each participant based on the number of data input that were one-to-one matched on the acquisition time collected by each participant’s three instruments. Subsequently, we calculated the proportion of time during which the light intensity exceeded 1000 lux in relation to the total recording time at the wrist, chest and eye levels, respectively.
The results are presented as mean±SD. Statistical analyses were performed using SPSS V.25.0. For the device comparison, a paired t-test was conducted to assess the differences in light intensity measured by HOBO and Clouclip, as well as by the two HOBO devices. Additionally, linear regression was employed to establish the correlation between the two devices. Subsequently, the differences in illumination received at the wrist, chest and eye levels were compared using a one-way analysis of variance (ANOVA). As a threshold of 1000 lux was adopted to evaluate outdoor activity, the proportions of light intensity surpassing 1000 lux in the three different positions were compared using a Χ2 test. Further pairwise comparisons were performed using Bonferroni correction. Moreover, the difference in light intensity between different positions under the condition of ambient illumination ≥1000 lux or <1000 lux was assessed using a two-independent samples t-test. The difference was considered statistically significant when p<0.05.
