Quote Originally Posted by growbe
During the propagation stage, lights should be left on as long as possible, up to 24 hours per day. Strong initial growth will make the young plants healthier and more resistant to disease, ultimately providing better yields. As the plants begin to mature, however, light duration should be reduced.
Plants use periods of darkness, too. During dark periods, plants continue to take in oxygen and give off carbon dioxide in a process called respiration.
I agree 100% except for the last sentence. (bold text) lol Think about that for a second...

This is one of the best aspects of indoor cultivation. You can control many aspects that mother nature doesn't bother with.

Bottom line with almost ANY plant is during propagation the more light the plant receives the faster it breathes (grows). Because of this, a good source of CO2 is absolutely REQUIRED for propagation under 24hrs of light. This creates a chain affect wherein good soil is also needed too.

I don't recommend 24hrs of light unless all other conditions are completely ideal...

I believe it HAS been proven that the light reduction over a period of time yields a healthier plant overall. I don't think it changes the actual AMOUNT of the yield but I do believe it has a HUGE affect on the quality and potency of the plant.

Always remember though, 12/12 is the MINIMUM required for growth. Never ever go below that. At least from my experience.