When do you replace your HPS bulbs?

great thread and very informative i needed to see something like this thanks all.

I use a high end photo light meter, set on a 4' stick taking reading in several places and after 6 months of use the light out put is

one half or less than a new bulb reads.

So I replace all my bulbs every 6 months ,might be a waste but I DON'T THINK SO

Daddy