Department of Kinesiology, Recreation, and Sport Studies, The University of Tennessee, Knoxville, TN
Company Annual Meeting
Our office will be closed Wednesday, January 20th due to our company annual meeting. We expect to resume regular business hours on Thursday, January 21st. If you need immediate assistance, please contact our Support Team and submit your inquiry. We will respond as quickly as possible. Thank you for your patience!
Detecting Indoor and Outdoor Environments Using the ActiGraph GT3X+ Light Sensor in Children
- Published on June 26, 2013
Experts recommend children spend more time playing outdoors. The ambient light sensor of the ActiGraph GT3X+ provides lux measurements. A lux is the International System’s unit of illumination, equivalent to one lumen per square meter. Few studies have established a lux threshold for determining whether a child is indoors or outdoors.
The purpose of the study was: (1) to assess the reliability of the ActiGraph GT3X+ ambient light sensor, (2) to identify a lux threshold to accurately discriminate between indoor and outdoor activities in children, and (3) to test the accuracy of the lux threshold in a free-living environment.
In part one, a series of reliability tests were performed using 20 ActiGraph GT3X+ monitors under different environmental conditions. Cronbach’s alpha was used to determine inter-instrument reliability. In part two, 18 children performed 11 different activities (five indoors and six outdoors) for six minutes each. The optimal threshold for detecting indoor/outdoor activity was determined using ROC curve analysis. In part three, 18 children at a preschool wore the monitor during a school day. Percent accuracy was determined for all conditions.
Part one: The devices had Cronbach’s alpha values of 0.992 and 1.000 for indoor and outdoor conditions, respectively, indicating high inter-instrument reliability. Part two: The optimal lux threshold was determined to be 240 lux [sensitivity=0.92, specificity=0.88, AUC=0.96 (95% CI, 0.951–0.970)]. Part three: Results of the school-day validation demonstrated the monitor was 97.0% accurate for overall detection of indoor and outdoor conditions (outdoor=88.9%, indoor=99.1%).
The results demonstrate that an ActiGraph GT3X+ lux threshold of 240 can accurately assess indoor and outdoor conditions of preschool children in a free-living environment.