how tall

im going to be using 400 watt MH for veg, HPS fpr flower, on a moving track, what would the max height of the plants be

All depends on the strain. Could be a 6' sativa or a 2' indica. Time will tell.

It depends on the height of your ceiling and the strength of your light. The tops of the plants should be about 12-18 inches from a 400 watt light on a light rail.

Remember, once you switch to 12/12 the plant can grow up to 100 % to 150% taller

what im trying to say is how far down will the light be effecteive, so ill know when to stop veg, if I veg to 2 feet it will go to 4 feet, in 5 gal pot about 13 in tall, ceiling 8 feet tall, afghani kush, will the light take care of a 4 foot plants,

if you veg to 2 feet and plant is indica will end up at 4 feet
if you veg to 2 feet and plant is sativa plant will end at 6 feet

a highbred mix of ind and sat based on mix end height to vary accordingly




a 400 w mh will give you whut you need in penetration for a normal veg unless growing big monster trees
i use a 4oo and a 25o together in a double bulb hood
i have heard the 6oo is the best reults for money and wattage

gluck

General rule of thumb for a 400, 3'x3' area and the light penetrates 3' effectively. I use a 400 and like to grow 24" to 36" plants.