2400mp bulb burned out?

I have a Dell 2400mp projector that I've been using for a while.  The other day, in the middle of normal use, the bulb shut off and the orange 'lamp' light came on solid.  Looked in the owner's manual, and this seems like a totally normal bulb burn-out.  Ordered a new bulb, and planned to install it today, but before I did I decided to turn on the projector one more time.... and the lamp lights up perfectly!  Anyone have any idea what's going on?  Does the orange light come on before the bulb is actually burned out, but when it's getting close?  Need to use this for a performance, so I want to know if I should plan on this shutting off again in the middle of the show.... but I also don't want to replace the bulb if there's more time left on this one.