Not out-side i'm afraid. They depend on the great big HPS in the sky. In my youth i had an outdoor grow that i tried to have a 12/12 flower in the middle of summer in Spain. I Did this buy working out the best 12 hours of the longer day the sun was highest for, then i would roll them into my dads garage that was completely dark for the other 12 hours. Needless to say it wasn't my best grow as this amount of daily calculation whilst stoned & surrounded by beautiful women & countryside is just not sustainable.