i ran a 400hps bulb in a 430 ballast for over a year before i noticed it was not a 400 ballast. it was given to me by a friend who told me it was a 400. so you can run i 400 in a 430 ballast just not the other way around. the 430 is much better. my first grow with that ballast was with a 430 bulb but i broke it at harvest so i got a 400 not realizing it had been a 430. when i finally realized i had a 430 ballast(now with only a 400 bulb) it made alot of sense why i got such a better yeild the first grow and could not seem to duplicate the results.