The Impact of Dynamic Light with Different CCT Ranges and Frequencies on Human Alertness

Light could have an acute effect on human performance, including task performance, alertness and phase shift. Most studies have investigated the alerting effect of static light. The aim of the present study is to investigate the effect of dynamic light of changing frequency and CCT range on human alertness and task performance. Ten participants including 7 males and 3 females took part to perform six phases of dynamic light by varying their CCT range and CCT frequency. There are six experimental phases: CCT ranging from 4000K to 10000K, with frequency at 2h, 1h, 0.5h, and CCT ranging from 6000K to 12000K, with frequency 2h, 1h, 0.5h. EEG alpha, beta power, 2-back and 3-back task and questionnaires were used to measure each subject. The results showed that, power in alpha range was significantly, i.e. lower after exposure in high CCT condition than low CCT condition. Beta power was also significantly higher in high frequency condition than low frequency. For both 2-back and 3-back tasks, participants perform significantly better in high CCT condition, but no marked difference between different frequency. It was also found that there is a significant different effect on the questionnaire score between different CCT ranges. In general, participants felt more alert in higher CCT range condition and higher CCT frequency conditions. The results can be used to overcome drowsiness after lunch, to increase alertness and to improve work efficiency.