As far as i know, weed grows in the spring/summer. When the days are long,hot, and the sun is intense. Hense having daylite for 18hours a day, dark for 6. (18/6), the sun is more intense and bright (6500K, daylight).
Harvesting season is winter/fall. Less intense light, shorter days (12/12), warm white (2700K).

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"the devil went up to washington, he was looking for a grow to squeal. he was in a bind cause it was drinkin time and he was willing to make a deal, when along came a young man named firebird growin and growin it hot, and larry calls the piggies up and says "boy lemme tell you what" - fdd2blk