Bulb/Ballast Issue

[watts]

I have a 400 watt xtrasun magnetic HPS ballast powering a 400 watt Ushio MH conversion bulb. It's been working fine. Not that old. I went to unplug it for about 40 minutes today. I plugged it back in and the bulb is lit but very very dim, like barely lit. I unplug it for 20+ minutes and plug it back in, same problem. I'm not using a timer. I can't figure out the issue so any help would be appreciated.

 

[Mr Blah]

Got another bulb to try? How long did you leave it plugged in?

 

[watts]

I just tried a 400 watt Hortilux HPS bulb and it's working fine. So I'm assuming it's the bulb. Why would the bulb even glow though? I figure it wouldn't work at all if it was bad. Inside the bulb looks ok to me, nothing exploded or bent out of shape.

 

[Mr Blah]

Just one of those things....Well at least I can't explain it.
Glad to hear it isn't the ballast.