The aim of this study was to determine the appropriate lighting conditions in an assumed office environment considering work efficiency and multiple levels of arousal. Eight healthy male college students participated in this study. The experimental conditions were correlated color temperatures of 3000 K and 6700 K, and illuminance levels of 400 lx and 750 lx. Each set of conditions was tested in both the morning and afternoon periods, for a total of fourlighting conditions. Work efficiency was evaluated based on contingent negative variation (CNV) using reaction time and error rate, and evaluations considered arousal level as assessed by alpha wave ratio, average amplitude of the early CNV component, heart rate variability, and level of drowsiness. Based on our results, the recommended illuminance is 3000 K at 750 lx in the morning and 3000 K at 400 lx in the afternoon.