I use the LUX meter with the HPS & MH bulbs and replace the bulbs when the lux starts to diminish at a set distance out and I use a infrared temp gage for the canopy and that helps me decide if the bulbs are dying or not.
By this summers end I will probably make the switch to LED's though.
Morning, I follow this pretty closely from GWE
https://www.growweedeasy.com/lux-meter
if you haven't bought a light meter and you have an Iphone I suggest getting the Photone app. Its cheaper and more accurate.
https://apps.apple.com/app/photone-grow-light-meter/id1450079523
I never worried about that when I used hps. The heat was always a concern. I replaced my bulbs once a year.
I use the LUX meter with the HPS & MH bulbs and replace the bulbs when the lux starts to diminish at a set distance out and I use a infrared temp gage for the canopy and that helps me decide if the bulbs are dying or not.
By this summers end I will probably make the switch to LED's though.
i replace mine ever 6 months ..... i hope 2 go led this summer .... do u have 1 in mind i like hlg i have one in veg now ...