well like this morning. I went to check it. It should have been on. It was off. The bulb was cool. I unplugged it and plugged back in. It started working but i dont believe it is anymore. It may have stayed on for 2 hours!!! I was waiting for it to cool back down. There is no smell! Humming and warm when the bulb is on or off???? It is humming and warm when the bulb is on. My lights are off 1pm to 5pm.you need to:
Never turn off the bulb until its 100% done warming up
never turn on the bulb unless its 100% cool.
Never turn off the light and then turn it on within 30 minutes at least
as for your problem, is the ballast still humming and getting hot, does it smell funky? Does the bulb look broken inside?
i have a new hps bulb that should be here tues. It is a digi ballast.i second goat on the this one. What kind of ballast do you have. Mag coil or digi? If there is no physical damage to the bulb upon close inspection i would suspect the ballast. The only way to know for sure would be replace the bulb. If it ends up beingthe ballast you still have a new bulb for your new ballast. I don't know about your bulb prefferance but you can get 600 w hps xtra bright bulbs on ebay for $35 shipped. I use them with no probs.
http://cgi.ebay.com/600w-600-watt-hps-hydroponics-sodium-grow-lights-bulb_w0qqitemz280334221252qqcmdzviewitemqqptzlh_defaultdomain_2?hash=item414538bfc4