It's very unlikely that an 8 hour dark schedule will work with anything other than autos, but the people who are saying that 12/12 is the only way are wrong.
Many strains will flower with less than 12 hours of darkness. Some indicas are happy to flower under 11 or 10 hours of darkness, whereas equatorial sats are usually closer to requiring 12/12. Hybrids are anybody's guess, depending on their genetics. There are many early flowering strains out there than will flower well before the equinox outdoors.
I won't comment on non-24 hour cycles, since I have never seen anything concrete either way, but some of the theory seems good. I once talked to an experienced grower who swore by 6/12, with the theory that plants only photosynthesize effectively for 6 hours per day, after which their efficiency starts to drop. He said that yield was only minimally effected, but he shaved 25% off his flowering time. I have no reason to doubt his word, but since I never saw the results for myself I consigned it to "possible", rather than concrete fact in my mind.
As the guy above me said, nature is more fluid than solid. 12/12 works, and is the easiest way to guarantee flowering, but it is not set in stone as the only way, or even the best way.
Many strains will flower with less than 12 hours of darkness. Some indicas are happy to flower under 11 or 10 hours of darkness, whereas equatorial sats are usually closer to requiring 12/12. Hybrids are anybody's guess, depending on their genetics. There are many early flowering strains out there than will flower well before the equinox outdoors.
I won't comment on non-24 hour cycles, since I have never seen anything concrete either way, but some of the theory seems good. I once talked to an experienced grower who swore by 6/12, with the theory that plants only photosynthesize effectively for 6 hours per day, after which their efficiency starts to drop. He said that yield was only minimally effected, but he shaved 25% off his flowering time. I have no reason to doubt his word, but since I never saw the results for myself I consigned it to "possible", rather than concrete fact in my mind.
As the guy above me said, nature is more fluid than solid. 12/12 works, and is the easiest way to guarantee flowering, but it is not set in stone as the only way, or even the best way.