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I would definitely get an HPS for flowering if it isn't too much more trouble for you (if you already have a switchable or the CORRECT digital ballast, or you could get a conversion bulb).
There are a lot of people that don't ever even bother with MH because everyone agrees that if it comes down to a MH or HPS for flowering you always go with the hps
Not that a MH won't do an adequate job, its better than using any LED set up for flowering, but 15% I would guess yes!

True

That's the info i've gathered as well.

Just looking to see if someone has done it first hand experience and has also flowered under HPS to compare the results.

Well lots of people have and that is why they don't use them to flower and why we are reciprocating what we heard from them
MH = Great for veg
HPS = Great for flower
MH and HPS = even better
Some people go nuts and have say 2 or 3 HPS for every MH in their grow room for flower, and 2 MH for every 1 HPS in veg

I've understanded this from day 1.

Anyone have first hand experience flowering under M/H ?