The effect of blue light on ROS production and cell viability. (A) Intracellular ROS levels were increased after exposure to blue light for 6 hours to 24 hours. There was 1.45-fold increase in ROS after irradiation for 6 hours, 1.72-fold increase for 16 hours, and 1.96-fold for 24 hours. ROS levels were determined by dichlorofluorescein (DCF) assay. Data were expressed as mean + SD. n = 5, *p< 0.001. (B) Cell survival, reflected by ATP content, was detected using Celltiter-Glo luminescent cell viability assay. After blue light irradiation for 6 hours, 16 hours, and 24 hours, ATP content was decreased to 87%, 68%, and 49%, respectively. Data were expressed as mean + SD. n = 5, *p < 0.05, **p < 0.001.