Lights question

I've got a 600w MH/HPS setup. I've been watching a lot of grow vids lately and I've noticed some growers will grow their veg out at a lower wattage and when they make the flip, they use higher wattage. For example, 400w for veg and then use 600w for the flip. I don't have a 400w bulb but I do have a dimmable ballast. Should I dim my 600w back to 400 for the veg or just go a full 600w for both veg and bloom?

600 all the way

im no expert but id say it would depend on when and if u hit the light saturation point.

http://www.marijuanagrowing.com/showthread.php?1506-Measuring-Light-Efficiency

when they are very small the plats cant take advantage of the very strong lights . but once they pass the 3 inch mark its time to turn up the juice they will grow very fast . any smaller then 3 inches you can use cfl if you want to save on the juice bill best a t5 . i use only 120 watts from led to veh but flower under 600 or 1000 watts . and i comes down to are you in a hurry . more power faster veg .

Veg areas are generally smaller than flowering areas so a smaller light can produce the same total light per area...

In this case my veg and flower tent are the same tent. One day I'll make the upgrade to veg and flower tent. It's small -2x4x5- and there won't be any more than 3 plants going at a time.

running a 600w mh @ 400w is cool

less heat, when your plants are in smaller pots less heat is better because smaller pots heat up faster and getting the roots over 21c or so can give you rot issues

plus why waste an extra 200w if a 600w hps is enough to cover them in their last weeks of bloom then 400w of mh should be more than ample to veg and start flowering them with