which bulb for what type of grow?

[slo-han]

Hey guy's and gals, Im considering a 400 watt unit for the fall, it comes with and MH bulb - I don't recall the value or use of MH or HPS. It can use both but will I need both? - -thanks slo

[Mega nute]

Hey Slo, some people swear that they have to start MH for veg. And HPS for flowering. The MH has more blue light which is good for veg. The HPS has more red for flowering! Now having said that, I have never used anything but HPS. You can raise a nice crop with just HPS. There are some issues with stretching if you don't watch! But I have always been able to bend and tuck or a fimming of the top not which is no more then a cut of top knot on a 45 degree angle. One last note, the HPS was the best all around light until L.E.D.'s. I have to tell you that I used a 400 watt HPS for a few years before I went to the 1000 watt HPS and now, the L.E.D.'s. Hope this helps Slo, Mega

[Schmokin]

If you have both MH and HPS then use the MH for veg and the HPS for flowering. If you can only have one bulb then it needs to be the HPS which works just great for an entire grow.
As Mega says though, LEDs are making great advances and a modern LED can easily perform as well as HPS for a fraction of the running costs. You need to get a good one though, there are lots of cheap imports available that will work fine for vegging but struggle to provide enough power for flowering.