MEASURING LIGHT AS A STIMULUS FOR THE HUMAN CIRCADIAN SYSTEM

摘要

Light is defined as radiant energy capable ofproducing a visual sensation in humans (CIE, 1978). Light incident on the human retina also regulates the timing of the circadian clock in the brain. Although there is no formal definition of "circadian light", recent research has shown that the spectral sensitivity of the circadian system is quite different than that of either the photopic (V_(lambda)) or scotopic (V'_(lambda)) luminous efficiency functions used throughout the world to measure light. Since neither of the conventional luminous efficiency functions represents the spectral response of the circadian system, it is necessary to develop new measurement devices to characterize "circadian light" for humans. Moreover, since both the duration of light exposure as well as the timing of light exposure are so important to the circadian system, a device to measure "circadian light" must also be able to represent light exposure accurately to the circadian system for extended periods of time. The Daysimeter (Bierman et al., 2005) was developed to measure circadian photic stimulus. It necessarily has two detectors to represent the subadditive response of the circadian system (Figueiro et al., 2004; Figueiro et al., 2005; and Rea et al., 2005) and has sufficient memory to capture circadian (and photopic) light exposures for seven consecutive days. It also contains accelerometers to record user activity patterns. The paper describes the Daysimeter and presents some new circadian light data showing differences in light exposure patterns for different subpopulations.