Bulb life is one of those "follow the masses things". There have been tests run by reefers who have access to very sophisticated test equipment that have provided general guidlines on bulb life. Usually the MH bulbs are used for approximately 12 months when using a standard magnetic ballast, and there have been claims of extending that life to 16 months when using electronic ballasts. Now at the end of 12 months, most of us cannot tell the bulb needs to be changed, that is because as a bulb ages, it slowly will shift the primary range in the color spectrum that it is generating light in. Often t an undesirable red/yellow shift which promotes the growth of undesirable algae. And if that algae gets a foothold in your tank, it is VERY difficult to erradicate.
The article at the link below is very good comparison on different MH bulbs, with different ballasts. Bottom line of the report is that the XM bulbs are one of the best in fulfilling the desired spectral output. Especially when you look at a cost comparison.
http://www.advancedaquarist.com/issues/oct2002/feature.htmThe author of this article, Sanjay Joshi will be presenting on lighting this month at the Seattle reef club meeting. A few of us will be making the trip to learn more about lighting our tanks. This should be a very informative presentation.
Rick
