I have just replaced the ballast in the fixture over my desk for the second time in less than 5 years. This is as much or more than the lamps. It is a 2 lamp 120V T8 electronic. The fixture is on a lot. What is the expected life of a ballast? (they are pretty low end ballast I am sure)
We have 75 buildings in our school system. Most are 277v on the lights and most are T8 2 or 3 tube. It's not uncommon to see ballasts last 7-10 yrs. With that said ... most of our rooms burn all day (no repeated on/off cycles); I suspect that has some effect on the life. Our newer schools have occupancy sensors that shut off the lights regardless of the switch position but they haven't been in long enough to see if it affects the ballasts. The ballasts and bulbs that don't seem to last are the gym fixtures that use 8 compact fluors (4 ballasts) per fixture.
I just changed the 2-lamp T-8 ballasts in one of the shop lights over my bench for the second time in probably five or six years as well. Like the OPís, it also gets a lot of use. I remember back when the T-8 electronic ballasts first came out, they would frequently burn out sometimes only within a year or two. Those GE Triad ballasts come to mind. To me anyway, the newer ones made in the last few years seem better as far as life span goes, but IMO, they still donít last anywhere near as long as the old potted magnetic ballasts used to.