Key result
Exposure to bright light with a high color temperature (6500 K) more strongly suppressed the nocturnal fall in core temperature and melatonin secretion than light with a low color temperature (3000 K).
Why the study?
Does exposure to high color temperature light compared to low color temperature or dim light affect nocturnal core temperature and melatonin secretion in subjects with normal color vision?
Does exposure to high color temperature light compared to low color temperature or dim light affect nocturnal core temperature and melatonin secretion in subjects with normal color vision?
Exposure to high color temperature light at night suppresses the normal nocturnal fall in core temperature and rise in melatonin more than low color temperature light.
Supports caution on high color temperature lighting at night for circadian alignment; extends spectral data but leaves open real-world sleep impacts.
A variety of types of artificial illumination has recently become available, differing in the quality of illumination and range of color temperature. In our previous studies we found that in subjects with normal color vision the nocturnal fall in core temperature and the increase of urinary melatonin excretion were suppressed by bright blue or green light, but not by bright red or dim lights. The aim of our present study was to examine from the view point of chronobiology whether the lights of different color temperature often used in everyday life may affect core temperature and urinary melatonin secretion differently. Experiments were carried out on five subjects with normal color vision. They were exposed for 5 hr (from 21:00 h to 2:00 h) to two kinds of bright (1000 lx) light of different color temperature (6500 K, 3000 K) with dim (50 lx) light as a control; after exposure they slept in darkness. Our main results were as follows: The light with a high color temperature of 6500 K more strongly suppressed the nocturnal fall of the core temperature and the nocturnal increase of melatonin secretion than the light with a low color temperature of 3000 K. This difference was particularly evident for core temperature during the sleep period following experimental illumination.
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Morita et al. (1996) studied Healthy subjects with normal color vision (n=5). Bright light (1000 lx) of different color temperatures (6500 K and 3000 K) vs. Dim light (50 lx) was evaluated on Nocturnal changes in core temperature and urinary melatonin secretion. Exposure to bright light with a high color temperature (6500 K) more strongly suppressed the nocturnal fall in core temperature and melatonin secretion than light with a low color temperature (3000 K).
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