What kind of bulb is that?
Looks like a spot light bulb.
I'd HIGHLY recommend replacing those with one or two 200w CFLS or 4-8 50w cfls.
Cfls are much cooler than those, that would make sense why you keep burning plants. It's the bulbs
200w Cfls you can place 4 inches away from plant foliage with a fan running to maximize light. Light dims down exponentially with distance so right now your plant might have 420w of light shining on it but it's only receiving a fraction of that.
Also consider putting that plant in a cabinet or some other smaller area that you can wrap with mylar or paint flat white to better reflect light back towards the paint instead of wasting it on coats and shoes or whatever else is in that closet.
BTW, autos are plant that can automatically flower without changing light schedual.
A consistent light schedual is very important, you shouldn't be giving it "about 14 to 18 hours" of light, you need to be giving it exactly 18 hours of light for veg or exactly 12 hours of light for flower. This also has to constantly be the same on/off time every day. You can accomplish this by using a simple timer.