When to change halides?

[2bafish]

Am currently running 3 250 watt 14k phoenix bulbs. Its been 16 months since my last bulb change. They still seem bright but when should i replace them. What recommended. Also do halide bulbs lose the blue color over time. Any input is appreciated.

[Aquattro]

I wouldn't run them past 12 months. The bluer bulbs, maybe even less. My 400w Radiums got switched out at 9 months or my corals would brown out..

[George]

How long do you run them everyday? and what ballasts? Those answers will determine how often you should change your bulbs, roughly. FYI, I am running my phoenix 250W 14K on e-ballasts 6 hours a day. I change them once a year.
Here are a couple articles in my bookmark that you may find useful:
http://reefkeeping.com/issues/2007-04/ac/index.php
http://kb.marinedepot.com/article.aspx?id=10857