1210s "light orbs"

My projector has two VERY faint orbs near the middle of the display area.  These are only visible when the display is projecting a black background.  I was wondering if this is a sign of some malfunction or if it might simply be a couple of dust particles that have landed on a mirror / lens.

I just read the suggestion that I should periodically open the lamp casing and shoot some compressed air in there.  I will give that a shot and see if it rectifies the issue.  I just thought I would ask just in case that doesn't fix it.

At a projection distance of about 15 feet the orbs are about 4 inches wide and they overlap.