How big of a difference in yeild would I see flowering with a 400W MD bulb compared to a 400W HPS bulb?
MH bulbs are not intended for flowering your buds will take much longer to develop and finish and may not be as dense as would be with a HPS.
There won't be a huge difference between HPS and MH but HPS tends to produce better bud If you want, just use the MH with 2100k CFLs
cool. I was thinking that the spectrum that the HPS puts out was tits for flowering and since the MD puts out a different light spectrum i might end up with so-so buds using it. The HPS is rocking so far so I'll stick with it, but next time I might try going the distance with the metal halide.
if you want to use Metal Halide like I said before in other posts use Ceramic Metal Halide from Philips it is full spectrum with more red than HPS and more blue than MH with considerable UVB output I got pics coming on Thursday of my bubbleberry and NL that I finished under CMH and they are the frostiest buds I have ever grown or seen in person that is for sure. UVB= THC production and the density is definitely there just not as much bud as might have been with HPS. Quality is definitely better with CMH but yield will be a bit more with HPS. That is why I might be doing a 600 HPS coupled with a 400watt CMH when I do my grow in my own place.