I'm using my 15 yr old Viking D1 and at times I leave it on the entire time I'm sewing, pressing and back to sewing. This could be 4 - 7 hrs at a time and as you can see its still going strong. Also I've learned how to change my lightbulbs myself and always have a spare in case it goes. I don't live near a large city to pick a lightbulb up quickly so always keeps spares of parts that might go more quickly than others. My last lighbulb lasted 5 years and still didn't go out but when I took it in for normal service the guy mentioned the bulbs (2) were just about ready to go out on me so had him change them both. Never fails when one goes out the other one is just on the tail of the 1st one to follow.
One time I left the machine on all night as I forgot I had left it on. I tend to do that with my iron too but it has an automatic off if left alone for a period of time. Just last night I thought I had left it on but this morning I found I had turned it off. Thank goodness.