A projector lamp inevitably loses brightness after each hour of use, which causes image degradation. We suggest you follow the specified lamp life hour rating as a guide to when the lamp may need replacing. For example, a projector with a 4000 hour lamp would require a lamp change once those 4000 hours are up. You can find light usage time stats in the Information page of the On-Screen-Display menu. This doesn't mean the lamp will suddenly fail when it reaches its estimated lamp lifetime. You can continue to use the lamp until complete failure, but doing so impacts image quality.