The influence of different wavelengths of light on human biological rhythms

The purpose of this review was to discuss the influence of light on humans in the environment, focusing the relation between the quality of light and human biological rhythms, and also to apply the results on lighting planning to a living space which takes into account human health and comfort. The main discussions were as follows: 1) The effects of light on the behavior of core temperature and melatonin vary depending on its wavelength. Light with long wavelengths, such as light with a low color temperature and red light, had little influence on the human biological rhythms. On the other hand, green and blue light--light of mid-short wavelength such as light with a high color temperature--had a greater influence. 2) From the relation between the stimulus received by each photoreceptor and the inhibition of core temperature and melatonin, it might be concluded that the photoreceptor responsible for transmitting light information that affects biological rhythms is M-cones. 3) A higher light intensity was required in the morning than in the evening to induce the inhibition of melatonin secretion. This result suggests the possibility of existence of a diurnal change of sensitivity of the photoreceptors (M-cones). 4) From all these results, it is proposed in the field of living environment and living engineering that light with a low color temperature should be used for low-level lighting at night, and high-level light with a high color temperature in the morning.