I havent ran one on 12 12, but im debating it. Everything ive read just seems like it will still run, just be smaller because its not getting as much light as it would on 18/6 or 20/4. My cab is on 12/12 with my cups for the party cup competition. Im gonna fill up my empty space with something so i might drop 1 auto in the mix. Ive got plenty of freebies to fill up the rest with photos though. When this finishes i think im gonna do an all auto run and try to get some big ones. If i do an auto ill let you know and you can watch. Ive got so many strains i want to pop right now i can hardly contain myself lol. Growing cannabis is definitely teaching me patience!