How often do you guys replace your HPS bulb?

I am coming up at 6 months of daily 12/12 use for my400 HPS bulb. I see no noticeable difference in intensity but since it degrades gradually I really can't tell. So how often do you guys change yours?

I change mine every 6 to 9 months. I've heard 6 mo for best efficiency.

i do it approx every 6mos or after i've done 2 runs with the bulb.

alright, thanks guys I'll get a fresh one for the next run.