So i was busy dinking around with my various ballasts n' such today, I had taken an HPS 400W ballast (without the ignitor) and hooked it up with a 400W MV, also in parallel with that merc was a 250W(i think? the lamp was unlabeled) halogen, i lit it up and the halogen was really bright for a bit then the merc kicked on and the   dimmed down a bit, slowly as the MV came to full brightness, the   went back to fullish brightness, but none of that is really the important part, So i had that set up going for a bit, then i accidentally hit the halogen with a screwdriver, the outer capsule did not break but the filament broke and what resulted was very interesting, first the filament broke of course it still glowed orange a little at the bottom of the capsule, then an arc established this arc went from blue to green then finally red, after it had turned red (this was in the space of 10 seconds) it extinguished and knocked the mercury lamps arc out aswell, while the arc in the halogen capsule was going the merc was also putting off a bit of a show, it was flickering between pinkish-red and its original colour (it is a coated lamp)