I am setting up a stealth compact grow box that will be using LED's and I want some supplemental lighting. I am considering buying a 250w flowering CFL's or 150W HPS. Which would be better to help with flowering? Also without a direct exhaust to the light will the HPS get to hot for a vented 42" X 36" area?
Depends on your ambient temps I paid $90 total for a 125w cfl and hood for it. I bought one for Veg, seems to work great! Never used one for flowering. Based on your requirements, I'd get a CFL. HPS puts off like 10 deg more heat alone even with proper cooling. The CFL you just need a fan above it to remove ambient heat tha collects in the box. The HPS heat straight comes off the light and makes everything hot hot hot! Seems like you've already chosen LED's as your main light source. Did you get a big panel? Adding HPS seems like it would drown out the LED's?
I keep the area pretty cool both in summer and winter. The 250w CFL is actually more expensive. I have about 520 CFM for my vent system. Would that be enough to remove the heat from either lamp? I got 2 of the 90w UFOs R/B and a 45w white LED panel to give me the rest of the spectrum.
I would go HPS, the intensity and heat gives it the right kind of stress to flourish. Don't worry about it "drowning out your LEDs, I have seen peppers grown using LED and HPS and they looked MUCH healthier than those grown just with HPS.
I am not really worried about it drowing out the LEDs but I think I am going to add the HPS to supplement the LEDs.