This may be a stupid question but I am kind of new to Metal Halide lighting.
I am growing a couple of citrus trees indoors under a 250W Metal Halide light I bought last year. The bulb in my fixture was made in 1999, I bought the fixture complete in Jan. 2009, and it has run 16 hours a day every day since then. Since I have put ~7000 hours on the bulb and it was used when I bought it I suspect this bulb is near the end of it's life. I just learned how much these things dim over their lifetime and using a couple of charts I found online it seems to indicate that by the 7000 hour mark my bulb will be producing about 45-50% of it's initial light output, and since it is probably much older than that (the bulb was quite black from use when I got the fixture) the light output is probably 40% or less.
I have 2 spare brand new 175W MH bulbs in my closet, and I am wondering if it is safe to use them in the 250W fixture? Will it damage the 250W ballast or destroy the bulb, or would it function perfectly fine as a substitute until I can find a new 250W MH bulb?
Also, does anybody know a good local place to get a new 250W MH bulb? If it matters it is the ED28 size, has an E39 base and is mounted horizontally. I found a seller on EBay in Ontario for ~$25 and was going to order from him but I know it will take 2 weeks or more until the bulb gets here, hence my question about the 175W bulb as I now feel a bit rushed knowing how crappy the current bulb is.
Thanks for any help