BACKGROUND The purpose of our study was to determine if the development of refractive errors night be associated with exposure to light emitted by incandescent or fluorescent lamps. METHODS 3377 students from elementary schools, junior high schools and high schools were examined, aged 6-19 years. Visual acuity was measured, and retinoscopy was performed after cycloplegia. The parents of all students examined completed a questionnaire concerning the child's exposure to light emitted by incandescent or fluorescent lamps before the age of two. The data was analyzed using the chi-squared test. RESULTS Sleeping till the age of two with a room light turned on leads to an increase in the occurrence of myopia (P<0.01). It was also found that light emitted by fluorescent lamps leads to more frequent occurrence of astigmatism (P<0.01). CONCLUSIONS Disturbance of the daily light/dark cycle over the time during which refraction develops may disrupt emmetropization and lead to refractive errors.