This experiment tests the change rate of students α & β brain waves under different illuminance levels combining with three color temperatures (CCTs) to indicate the influence of light spectrum on human physiological rhythm.The result shows that the brain electrical activities have significant differences under various CCTs and illuminance levels.The excitement and sensitivity of brain are roughly proportional to the light CCTs and illuminance. Brain electrical activities are more sensible to high CCT illuminations. Keeping mental work in the same time period with the same study intensities, brain fatigue comes earlier and stronger in excitable state at high illuminace and high CCT illumination than in peacful state at low illuminance and low CCT illumination.This situation leads to the learning efficiency of students decreased sharply.An interesting phenomena is that when working in low illuminance and low CCT environment, learning efficiency of students rises with time passing by.That indicates this kind of lighting environment may lead to awake effect of brain. In some environments which have the same illuminance levels with different CCTs that bring about the similar brain activities, learning efficient change rates are different because of the diversity of light spectrum which may induce the different stimulus intensity.Further research work is needed to explain this phenomenon.This experiment points out that the long-term mental workload character during the process of study and comprehensive effect of time accumulationmust be seriously considered in classroom lighting design.