Replace them every 9 months I do. I have had this arguement with FW
folks before whom insist that PC
bulbs just dont wear out and I have given up as its a lose lose situation. Both parties know they are right and that never works out good.
In the saltwater world there is a noticable difference between bulbs that are 9 months old and new bulbs over a tank. The higher K
bulbs will slowly fade into lower K
spectirum of light output as the bulbs age.
If you doubt their has been a noticable change I suggest the following. If your tank has bulbs that are side by side I suggest changing out one with a new bulb of the same K
rating as the old bulbs. Then look at the tank with one side having anew bulb and one side having an old bulb. If you dont have that ability then I would take a photo of the tank with the old bulbs and then take a photo fo
the tank with the new bulbs. Preset the white balance with the old bulbs and I suspect you will be amased at the differences between the two images that would have only been taken moments apart.