I had a very close call last weekend when I returned home and walked inside to a very strong odor of smoke and burned plastic. I immediately thought of my hydroponic tomatoes with the 600 watt high pressure sodium bulb with ballast that does get warm when operating. My suspicion was confirmed and the ballast appeared to have overheated and caught fire while I was gone. Luckily it was sitting on a metal table and the fire burned itself out when the circuit breaker tripped and cut power.
The smoke smell is still present and will probably hang around for a while. I'm not quite sure what caused the device to overheat, but it did send a chill up my spine when thinking of what could have happened. I consider myself pretty lucky.
I cleaned up the mess and relocated my plants to metal shelf rack and hung up one of my seed starting florescent lighting systems above the pots for now. I am afraid it may not be strong enough for the plants when they get larger and I may have to come up with a more powerful lighting system.
The plants seem to have weathered the mishap just fine despite the fact that they were without light for a while intil I got the replacement system set up and functioning. Commercial grow lights can be expensive and I will have to see just what I can afford.