Poor picture quality on Infocus SP61md10 (RCA HD61THW263)

I have a Infocus SP61md10 (same as RCA HD61THW263). It worked fine for about the first year. Then it started getting darker and has been very dark for the last 18 months. I have adjusted the brightness to maximum. The manual states that when the lamp goes out I will get a 5 flash on the indicater light. This has not happened, so to me this indicates that the projection lamp has not failed. I thought that the projection lamp might get darker as it approaches failure, but after 18 months???? Has anyone experienced this problem (a dark screen, not completely black but a very poor quality picture). Due to the very high price of a new projector lamp, I hesitate to purchase one if the problem could be caused by something else (maybe the ballast, or something else that I can't imagine). I have searched for a bulb only, but have not found one for this TV set.