When do you replace your HPS bulbs?

[LOC NAR on probation]

Replace once a year is a good rule for running 12/12 year round.

LOC NAR on probation Reviewed by LOC NAR on probation on 04-09-2011. When do you replace your HPS bulbs? I coming up on the completion of third grow with my current HPS bulbs (600 and 400). Just wondering when they start to lose effectiveness and when you experts say its time to get new one. Feedback appreciated :) Rating: 5