Hello Stellybutton,

Welcome to the boards. Sorry nobody piped up on this, so I'll give you my take.

I'm a firm believer in changing out HPS bulbs after 2 grow cyles of 12/12 or abt 16 weeks or so of use.

I just mentioned somewhere else that just 10hrs of use equals a loss of abt 20% of the Intial lumens you started with and it continues down steadily after that. That BTW is according to Hortilux, that makes some pricey bulbs.

I use cheap "generic" bulbs and buy them by cases of 6 at a time.
Tho recently in a partnered grow I sprung for some PSMHs from SunPulse (1000w) and they cost abt $160 each, sooo I might try to use them longer. Wait, I already have. Time for me to check them with a light meter.

OM