Typically the bulbs are rated for a certain number of hours, and there is a meter that keeps track of how long the bulb is on (ok, so I'm not sure about DLP bulbs, but it is true for projectors). Also, I don't know how these bulbs work, so I can't say if this type of problem is related to the bulb.
Anyways, poke around your TV and see if there is some sort of power-on meter.








