I replace my Hortilux 1000's after every 2 crops. I only VEG them under those lights for 2 weeks and flowering for about 65 days.
Sort of depends on the proverbial "cash situation".
I noticed that the lifetime of the bulbs far exceeds the # of hours in one flower cycle.
If cash allows, every 6 months.
Right now Santa took my HPS ballast back to the North Pole.
That capacitor was replaced ... but it turns out it needs a new power cord.
I replace my Hortilux 1000's after every 2 crops. I only VEG them under those lights for 2 weeks and flowering for about 65 days.