so im getting ready to order a 400w hps growlight with tha hood and ballast and everything.. and i was ganna use the hps light for flowering and get a MH light for vegging... so i was wondering do i just needa btuy a MH bulb or a whole new hood and ballast and everything do i just needa buy a MH bulb and screw it in where tha HPS once was? sorry for my stupidity
A hood and socket should take any type of HID bulb. As for ballasts, there are separate MH and HPS ballasts and they also make switchable ballasts (2 in 1). If you try to fire an HPS bulb in a MH ballasts, bad things will happen. Its actually not required that you veg with MH. You could do both cycles using an HPS. Not a huge difference in growth.
If that is a digital ballast then it will run both MH and HPS. If not, and if it is not a switchable ballast, then it is made to run only one or the other. If it is a HPS ballast you can run a MH conversion bulb off of it, which is a special MH bulb made to run off HPS ballast. Always match bulb wattage and ballast wattage.