A question...

I want to ask a question; how often do the new bulb get through with a cracked arc tube (not just automotive HID bulb - any HID bulbs in general)? I have noticed this on my modified HID spotlight right after turning it off - the crack was very hard to see, which is only apparent and easily noticeable when the arc tube itself is at 800 - 1,000 degrees. I was wondering how common is it that the bulb occasionally leave the factory with a dodgy arc tube.

I will relamp my DIY spotlight soon as I don't want it to blow up on me.

I'd say that the bulb was cracked on installation or handling after testing. The Xenon inside would have leaked out if it were defective and probably would not have struck an arc. It gets expensive rather fast doesn't it?

I had a bulb break on me this past week. The bulb was rated at 350 watts and previously been overdriven at 500 watts. This time, 30 seconds after the arc being struck, pow!. Magic smoke from the bulb and small glass shards within the light. This time I lucked out that the mirror wasn't damaged. With my recent luck, I don't know how that happened.

That's possible. I had to gingerly handle the Xenon Metal Halide bulb as I am paranoid of it popping in my face - it's possible it was handled roughly at the factory.

And, that's good you didn't get hurt. The HID bulbs like to fail spectacularly, thus strict driving rating and handling, although some lower wattage HID bulbs can resist rough handling (ie. Xenon metal halide bulbs installed in car headlights).

Occasionally they fail hard with little warning (change in emitted color) or no warning at all, even if they have been gingerly handling and fed properly. What I didn't understand here is that the metal halide bulb installed in my DIY spotlight light up just fine even if there's a problem with the arc tube - probably because it's brand new.