Will a 400 watt MH/PSMH bulb work on a 400 watt HPS ballast? Don't worry about the ignitor, because it will be removed if needed.

Any answers?

In my experience they have worked, although mercury lamps tend to cycle on HPS ballasts, or at least some of them, mh lamps I have not run longterm on HPS ballast, but I had very fully run up a few and the went to full brightness.

400w HPS seems to underdrive the lamp slightly when I compare it to an actual Mh light with proper gear (incandescent is there so you can see those are two different lights... Prevent confusion)

Here is mercs, it is slightly underdriven, but has not cycled yet, they'll work, but I'm not sure how good for the lamps it is...

While I always recommend you match ANSI codes of both ballast and lamp, I can tell you that a 400w MH lamp (M59) CAN work on a 400w HPS (S51) ballast...but not perfectly as HomeBrewLamps stated. I know of a business that relamped all of its 400w HPS parking lot fixtures with standard M59 lamps and it worked fine, the lamps lasted about their usual rated life of 18,000 hours. They are now on their second relamping with the metal halides and still no issues with the HPS ballasts. So, as far as the combination being damaging to the ballast...I dont think theres a problem. However, the MH lamp will run at reduced power, so if youre looking for highest performance and output this is not the way to go. I tested this combination with a watt meter between the lamp and the ballast and the lamp is in fact only running at 350w, which in most cases is still enough to vaporize enough halides to get the lamp close to its rated color, it will look just slightly cooler though compared to running on its rated ballast.

Thanks for the answers! Also, does color temperature affect the power requirements?

Colour temperature should not affect the power requirements.