Int. J. Environ. Res. Public Health 2011, 8(11), 4272-4283; doi:10.3390/ijerph8114272
Article

Estimation of Effective Day Length at Any Light Intensity Using Solar Radiation Data

Received: 16 September 2011; in revised form: 19 October 2011 / Accepted: 4 November 2011 / Published: 10 November 2011
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract: The influence of day length on living creatures differs with the photosensitivity of the creature; however, the possible sunshine duration (N0) might be an inadequate index of the photoperiod for creatures with low light sensitivity. To address this issue, the authors tried to estimate the effective day length, i.e., the duration of the photoperiod that exceeds a certain threshold of light intensity. Continual global solar radiation observation data were gathered from the baseline surface radiation network (BSRN) of 18 sites from 2004 to 2007 and were converted to illuminance data using a luminous efficiency model. The monthly average of daily photoperiods exceeding each defined intensity (1 lx, 300 lx, … 20,000 lx) were calculated [defined as Ne(lux)]. The relationships between the monthly average of global solar radiation (Rs), N0, and Ne(lux) were investigated. At low light intensity (10,000 lx), Ne(lux) and Rs showed a logarithmic relationship. Using these relationships, empirical models were derived to estimate the effective day length at different light intensities. According to the validation of the model, the effective day length for any light intensity could be estimated with an accuracy of less than 11% of the mean absolute percentage error (MAPE) in the estimation of the monthly base photoperiod. Recently, a number of studies have provided support for a link between day length and some diseases. Our results will be useful in further assessing the relationships between day length and these diseases.
Keywords: solar radiation; effective day length; luminous efficiency; light intensity; circadian rhythm
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MDPI and ACS Style

Yokoya, M.; Shimizu, H. Estimation of Effective Day Length at Any Light Intensity Using Solar Radiation Data. Int. J. Environ. Res. Public Health 2011, 8, 4272-4283.

AMA Style

Yokoya M, Shimizu H. Estimation of Effective Day Length at Any Light Intensity Using Solar Radiation Data. International Journal of Environmental Research and Public Health. 2011; 8(11):4272-4283.

Chicago/Turabian Style

Yokoya, Masana; Shimizu, Hideyasu. 2011. "Estimation of Effective Day Length at Any Light Intensity Using Solar Radiation Data." Int. J. Environ. Res. Public Health 8, no. 11: 4272-4283.

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