Optimum days means the longest or 12 hours /equinex or the shortest day hours in a particular place over a period of the year. Therfore, optimum days in the tropics are: End of Sene 14, Meskaram 13, Thahisas 12, Megabit 12 and Sene 14 . Where as optimum days in the temprates are: End of June 21, September 23,December 21, March 21 and June 21.