when to replace HQI lights?

[hammcd]

Ive got a 150w Coralife HQI running a 14k Phoenix bulb. The bulb has been running since 4/5/11, so just over 7 months at 7.5 hrs per day. I was told that most HQI bulbs start to degrade right around 7 months and while you can keep them until 9-10 months, to maintain the best light youd replace them every 7 months...is this what most people do...or do you replace later like 9 months and change the photoperiod to componsate?
thanks

 

[hammcd]

not enough money to change ballasts or fixture at the moment so lets assume it is putting out enough light...how often should i change the HQI to be safe without testing the par...does everyone else use the 7 month rule?

Edit: ahh just read the article..thanks for the link

Edit: also, if i wanted to change the coralife ballast to an icecap or something similar, is that easy to do...this is the fixture i have as it comes with the biocube HQI system:
http://www.marinedepot.com/Coralife_Aqualight_Advanced_Tank_Mount_1_150_W_14_000K_HQI_Double_Ended_Metal_Halide_Pendants-Coralife-ES53601-FILTFIMHPDDE-vi.html">http://www.marinedepot.com/Coralife_Aqualight_Advanced_Tank_Mount_1_150_W_14_000K_HQI_Double_Ended_Metal_Halide_Pendants-Coralife-ES53601-FILTFIMHPDDE-vi.html</a>
could an icecap work with this?

 

[hud3339]

I ran my 250w Phoenix 14k for 6-8 months then I would change it, I now run led's so I don't change anymore.

Edit: I ran my 250w Phoenix 14k for 6-8 months then I would change it, I now run led's so I don't change anymore.

 

[hammcd]

yeah i need to just buy an AI SOL

 

[mcphock]

I changed my HQIs every nine months and never had an issue with that. Although I too have jumped on the AI wagon.

 

[hammcd]

what AI did u get and for what sized tank?

 

[mcphock]

I have 4 over my 120. Sol Blues.

 

[schwaggs]

I used to run my 250W HQI Phoenix bulbs for 18 months. I tested PAR once when changing bulbs and measured similar results to the article linked above. I also never had a problem with burning or such when replacing the bulbs so that leads me to believe output was not that significantly different from 18 month old to new bulbs. I replace them now at 12 months attempting to avoid algae growth from spectrum shift but that is not proving too helpful.