%0 Journal Article
%T Circadian light
%A Mark S Rea
%A Mariana G Figueiro
%A Andrew Bierman
%A John D Bullough
%J Journal of Circadian Rhythms
%D 2010
%I BioMed Central
%R 10.1186/1740-3391-8-2
%X The suprachiasmatic nuclei (SCN) in the hypothalamus host the master circadian clock that organizes and orchestrates the timing of all daily biological functions, from complicated physiological systems to single cells. The SCN in humans have, on average, an intrinsic period slightly greater than 24 hours [1] that is modulated by the temporal pattern of light and dark on the retina. As a result of the earth's rotation on its axis, the temporal pattern of light and dark on the retina synchronizes the SCN to a matching 24-h period. Recent research has demonstrated that disruption of the natural, 24-h pattern of light and dark from rapid flight across time zones or from rotating shift work can lead to a wide variety of maladies, from poor performance to sleep loss, weight gain, and even breast cancer [2-9]. Because it is increasingly evident that retinal light and dark exposures can profoundly affect human health and well-being, it is increasingly important to be able to quantify both light and dark as stimuli to the human circadian system.The present paper deals with the evolving definition of circadian light. Technically, the adjective circadian must be used to modify the noun light because light is defined specifically in terms of optical radiation capable of producing a visual sensation in humans [10,11]. Strictly speaking then, light cannot be used synonymously with optical radiation capable of producing a non-visual, circadian response in humans or with optical radiation producing a visual response in another species. Nevertheless, in the vernacular, light is used as a term to describe optical radiation with a spectral power distribution anywhere within the "visible region" of the electromagnetic spectrum (approximately 380 nm to 730 nm), irrespective of its biological consequences. Moreover, the term light is always used, with or without strict regard for its ability to stimulate human vision, as a noun to describe the stimulus to rather than the response from a
%U http://www.jcircadianrhythms.com/content/8/1/2