Aiming at the non-visual effects of optical radiation of the flat panel display with light emitting diode backlight on human circadian rhythms, an experimental system is designed using a model of the evaluation of the circadian factor. By the method of average radiation in total space, the circadian factors of different pictures displayed on flat panel display with light emitting diode backlight are measured, and the pictures are all from the program of Average Picture Level in the International Electrotechnical Commission standard. It is found that the circadian factors of flat panel display with white and majority of colorful backgrounds are above 5.0, which are much stronger than ordinary lighting source, and are closely related to the content is displayed. The result suggests that the non-visual effect of the optical radiation of flat panel display on human circadian rhythms should be considered.