Jimster said:

HIDs lose some of their initial brightness and can have altered light spectrums from when they were new. I have noticed a difference between bulbs with 2 grows on them, and a new bulb, side by side, measures brighter. What does the arc tube look like? When they are ready to be replaced, at least in my judgement, is when the tube turns darker, or sort of burnt looking when not running. When new, the tubes are clear and slowly stuff seems to accumulate on the sides, reducing efficiency. Some might be better than others at having longer lives. FWIW, Eye Blue Hortilux, one of the better manufacturers of bulbs, seem to have less brightness compared to others, although the spectrum is more balanced. I also found that using HPS gives me a considerably larger yield than regular MH. I try to use HPS and 10K finishing bulbs during the last few weeks, prior to that I use a HPS and 3200K MH for initial flowering. I swap out the HPS for a 6K bulb for vegging... using both the 6K and 3200K temp bulbs for vegging. It's a simple bulb change, and since I'm using old school magnetic ballasts, I use a 1000w MH to HPS conversion bulb... best investment I made in 35 years! The previous best investment was the old school magnetic ballasts I bought in the 70s... still humming along!

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