Inappropriate lighting level causes digital eye strain among smartphone users. This experimental study employed 33 students aged 12-15 years in 3 lower secondary schools in Pathumthani province, Thailand. Amplitude of accommodation (AA) was measured by using the minus lenses method and compared between pre and post experiment under 3 lighting levels (50, 300 and 600 lux). Data were collected from 15 June to 30 August 2016, and analyzed by repeated measures ANOVA. We found the amplitude of accommodation and speed of visual task were significantly different between pre-test and post-test among 3 lighting levels (p<.01). The change of AA was increased most in 50 lux, followed by 600 lux and 300 lux, respectively. The environmental lighting condition and prolonged smartphone use in children might cause adverse visual and health effects. Parents and teachers should advise their children on proper and limited use for health and safety.
