Bulb Performance?

[jhornik]

I've heard certain bulbs hold there PAR longer than others, is this correct or does anyone know where I can find info on this? For instance, I run 2 400W XM 15k on a PFO ballast and am looking at getting Radiums but heard there PAR drops signifigantly after just a few months.

Thanks,

Josh

[Rickyrooz1]

Here is a good link.
http://reefkeeping.com/issues/2007-04/ac/index.php