summer solstice is the longest day of the year, the amount of day light will start to decrease after this by about 2 min a day. but this is for the uk, id assume it would be the same there.
doest make too much difference i ahve noticed, cause if got some plants out side and they have been growing for about 7-8 weeks now and some of them are starting to show sex. which is strange cause they dont normally do this for another month or so.

psy