i think cool col is correct though;light/heavy days are a good idea. i dont do them , but i know they work quite well (West side training), so it wouldnt hurt. But I also do heavy and light in one work out (a variation of 5b5, which works both types of fibers). This seems to be working for me quite well, although the volume might be considered high by some people. Here is a chest work out that I do :
1 or 2 light warmup sets (probably just the bar)
5x3 heavy flat barbell bench
5x5 heavy incline barbell bench
2x10 light weight incline dumbbell press
2x10 light weight dumbbell flat flies
once every 7 days. heavy weight, low reps for one type of fiber, lighter weight, heigher reps for the other, but this volume is quite high that if i do 2x/ or 3x a week i will definately over train.