I am wondering if it is safe to run standard probe start metal halide, standard pulse start metal halide, mercury vapor, and HPS retrofit lamps for mercury vapor ballasts on digital aquarium and grow light ballasts. I especially would like to know if Westinghouse Econolux and Sylvania Unalux HPS lamps can safely operate on digital grow light ballasts and aquarium ballasts safely.

Seeing as how a lot of digital ballasts are only designed for certain lamps, and need the correct lamp to function properly, I'm going to say no. And I really wouldn't want people trying just in case something gets damaged or a fire starts from it!

Adding to this, as I have said before, I only advocate running lamps on anything other than the correct ballast when that ballast is unobtainable, and even then only use a ballast that is as close a match as possible. That's what the ANSI code system is for. If you don't have the right ballast but it is available, get one. Save up for it if you don't have the money right now..!

Experimentation within certain limits is fine, but running lamp/ballast combinations that may be unsafe and could cause damage or injury isn't advisable, and I don't advocate discussing how to do it here.

I've had minimal problems running ceramic halide, probe start MH, pulse start MH, or HPS lamps on electronic ballasts. Virtually all HID "grow light" ballasts simply shove rated power into the lamp regardless of lamp type. Constant power, rather than constant current. This is because it is expected that the user switches between lamp types periodically to optimize growth at either vegetative or flowering stages of their... "tomato plants".

If the grow light ballast is "high frequency"like 100Khz-some CMH lamps will fail  QUICKLY on a HF ballast.Read the information about the lamp on the box or package!Many say NOT to run their bulbs on a HF ballast.HF bulbs are DESIGNED to run on HF ballasts and so marked.The ballast will say on it if its HF.

Yeah, that's the one exception, although I never figured out why. (Do you know?) All of the 50-150W ceramics I've had run fine on electronic ballasts, but the 400W variety I have did not.