Circadian effect can be characterized by midnight pupil size

Abstract

This study investigated whether the effect of circadian effect can be characterized by midnight pupil size. A phosphor-converted LED and an RGB LED with the same photopic luminance and color temperatures but different circadian luminance were selected as the experimental light sources. The steady-state pupil diameters stimulated by these two LEDs’ lighting were obtained by the infrared video, which were affected by photopic and circadian effects together. Twenty healthy volunteers were tested at different times of a day for five working days. It was found that the steady-state pupil size stimulated by these two LEDs were significantly different at midnight, but showed no significant difference in daytime, which indicated the circadian effect can be characterized by midnight pupil size. This study was very important for the design and evaluation of healthy lighting.