Effects of the morning irradiation of light with different wavelengths on the behavior of core temperature and melatonin in humans.

Following the previous studies on the influence of light with different wavelengths on human biological rhythms during nighttime, present experiments were conducted to investigate the influence of morning light on the behavior of the core temperature and melatonin in humans. The experiments were carried out in four subjects with normal color vision. The subjects were exposed between 4:00 h to 9:00 h to red, green and blue light of 1,000 lux and 2,500 lux, and with an incandescent light of 50 lux as control. The main results were as follows: No differences in the behavior of core temperature and melatonin were found under the influences of red, green and blue light of 1,000 lux and the control light of 50 lux. On the other hand, a tendency to promote the increase of core temperature and the fall of melatonin secretion was found after exposure to green light of 2,500 lux, compared with control and red light. These results indicate that the behavior of core temperature and melatonin differs according to the wavelength of light, and that the phenomenon arises with morning as well as nocturnal irradiation. However, the intensity of light required to bring about the phenomenon seems to be different between morning and evening; an irradiation of 1,000 lux x 5h at night in the previous report, and one of 2,500 lux x 5h in the morning in the present experiments, were found to be necessary for green light to cause the effects.