Figure 21From: Transdisciplinary unifying implications of circadian findings in the 1950sTerminology follows usage in physics. The broader division of biosphere spectra into 3 domains uses the circadian range of 1 cycle in 20–28 hours as a reference for frequencies (not periods!) higher (ultra) or lower (infra) than circadian, in keeping with precedents of nomenclature in physics.Back to article page