bulb or ballast problem?

[DMK]

i posted this also in lighting forum but knew it would get more looks here:
my MH bulbs are overdue for being changed. they're 18 month old geiseman megachrome 14.5K 250W, run off of a PFO dual HQI ballast. in past few weeks i've noticed 1 bulb either take up to 20 min after other comes on, before it lights up, or out of nowhere 1 bulb just shuts off and then comes back on within a few minutes. is this a sign of old bulbs ready to go or a ballast problem? all equipment only 3 years old, and it good shape, kept clean and dry and free of salt. i hope it's just a sign of old bulbs.

 

[j0tca]

Most bulbs have a total lifespan of about 4000-6000 hours. At 18 months, thinking 10 hours a day that's 5400 hours. You're bulbs are well into the failure range and my guess is that it's the bulbs.

Don't look for further problems when you know of one already.

 

[Wiskey]

The way to tell would be switching the bulbs, put the working one on the non working one's side and visaversa, if the previously bad bulb, keeps being bad, then you know it is the bulb. If the one that worked fine before, now does not then you know it is the balast.

HTH,
Whiskey