The Progression of Circadian Phase during Light Exposure in Animals and Humans

Under normal conditions of exposure to light and darkness, the circadian pacemaker is exposed to steeply fluctuating light intensities. For a human being, clouds, shades, retreating in a building, closing one’s eyes, and electric lighting all modify light intensity as provided by the sun in major ways (Beersma et al., 1999). The circadian pacemaker uses the whole fluctuating ligh