Illumination at Twilight
- 1 January 1963
- Vol. 14 (1) , 9-+
- https://doi.org/10.2307/3564956
Abstract
The nature of light units is discussed. Methods of its measurement in the conditions of low light intensity during and after sunset are described. It is emphasized that, with a clear sky and with no obstruction by trees, etc., the light intensity can be predicted with considerable accuracy for the entire period of twilight; it depends, of course, upon the latitutde and the date. The duration of activity of many crepuscular animals (e.g., mosquitoes) is rather rigidly controlled by the amount of illumination and the rapidly of its change. The crep is elaborated as a useful unit. It is calculated as the time of day minus the time of sunset, divided by the duration of twilight. The crep is positive after sunset and negative before sunset. Several tables gave corrections, sun''s altitude corresponding to crep, illumination corresponding to positive altitude of the sun, etc.This publication has 1 reference indexed in Scilit:
- Twilight and the ‘Crep’ UnitNature, 1961