MH bulbs

[Samw]

Here's some info for this old thread. I came across this article as I was Googling for Phoenix bulbs. It claims that the MH bulb that is being tested lost around 20% of its output by month 6. By month 12, it has lost 25%. By month 18, it has lost 30% of its output. By month 24, it has lost 34%. By month 27, it has lost 37%.

Light Output of the Phoenix 14,000K DE MH Bulb Over Time

http://reefkeeping.com/issues/2007-04/ac/index.php

"The light output of the six Phoenix bulbs shows an initial decline over the first three to four months and then levels off at about 75% of their initial output. From these data I raise the question: “If a bulb is not replaced at six months, when it has lost 20% of its output, then why would we replace it at 12 months when its output has fallen only another 6%?” It may be more cost effective to plan the lamp number and placement based on 70-75% of the bulbs' initial output levels. "

"this bulb would appear to still maintain 70% of its output at 18 months, 66% at 24 months and 63% at 27 months of use. "

Originally Posted by howdy20012002

I have a question...
For MH bulbs, do u wait to change them once they burn out?
Or do they lose their wattage as they get older like PC?
If yes, how often should u change them...my 90 came with the used MH bulbs and I am not sure how old they are.
As well, is there really that much of a difference in the different brands of bulbs?
Thanks for the info
Neal