If streaks are visible on a projection screen, what should be done in order to alleviate the problem?

Question

Quizplus · Accepted Answer

Clean the projector's focusing bulb
If streaks are visible on a projection screen, the projector's focusing bulb should be cleaned. The most common cause for streaks on a projection is improper cleaning. If the focusing bulb or glass slides are cleaned with a moist cloth, the streaks that are left behind will be projected on to the screen.

If Streaks Are Visible on a Projection Screen, What Should