Interger, day of the year (1..365) or (1:366) for leap years; or an object of class Date, or a characterr Date or character like as 'yyyy-mm-dd', e.g. '1982-11-23'
Value
Daylength in hours
References
Forsythe, William C., Edward J. Rykiel Jr., Randal S. Stahl, Hsin-i Wu and Robert M. Schoolfield, 1995. A model comparison for daylength as a function of latitude and day of the year. Ecological Modeling 80:87-95.