I've notice that even the color corrected HPS bulbs produce more sparce growth than say a Hortilx blue MH at 6500K.

I've also noticed that it takes about 2 weeks of 12/12 before growth slows and flowering begins.

Given this, it seems it is better to keep plants under the MH bulb until flowering actually begins, about 2 weeks of 12/12. Then put them under the big HPS for flowering.

Anyone agree?

Huuu?

I never thought of that before.
The first 2 weeks of flowering are like a growth spurt. It's actualy in flowering mode during the growth spert.
Your point makes sence though.
It would also save some $ if you had a big op.

I'v allways been a fan of hps and cfl togeather for flowering. Get all spectrums of light.

I use MH the first two weeks of flowering and then go to HPS+6500CFL. Works for me.