I know HPS arc tubes will still flicker and glow shortly after the bulb has expired, as I experienced this not too long ago. I thought that Halide bulbs were supposed to go out altogether at the end of their lives, but I've yet to see one burn out. But since it a conversion bulb, maybe it would still react like an HPS that's prematurely burned out.

Buy another bulb, hopefully that'll fix it. If not, it could be any range of things. Good luck! :thumbsup: