On the Role of Exponential Smoothing in Circadian Dosimetry

The effects lighting has on health through modulation of circadian rhythms are becoming increasingly well documented. Data are still needed to show how light exposures are influenced by architecture and lighting design and circadian dosimetry analyses should provide duration, phase and amplitude measures of 24 h exposure profiles. Exponential smoothing is used to derive suitable metrics from 24 h light measurements collected from private dwellings. A further application of these modified exposure time series as physiological models of the light drive is discussed. Unlike previous light drive models, the dose rate persists into periods of darkness following exposures. Comparisons to long duration exposure studies suggest this type of persistent light drive model could be incorporated into contemporary physiological models of the human circadian oscillator. Exponential smoothing is used to convert noisy light exposure time series into circadian variables for amplitude, phase and duration of light exposures (or photoperiod). This modifies the reciprocity view of dose calculation, and matches the duration-response of melatonin suppression to light. As well as applying these calculations to personal light exposures, available light exposures within buildings can be analyzed using these metrics to investigate the effects of design on circadian entrainment. Data for a sample of private UK dwellings are analyzed in contrasting seasons.