Best way to do searchlight effect, moving light spots, how?

[BdR]

For a game idea I was wondering, what is the best way to do a searchlight effect?

So I mean the entire screen is darkened, except for a few circles of light that move across the screen. Ideally the light circles could move independently from each other, so one moving up and another moving to the left. I understand that you can make the screen darker by adding a black Graphic rectangle over the entire screen, and then setting its Alpha to 0.5, but there need to be moving holes in it so to speak.

See the video below for a scene from the Amiga game "Hostages", that is kind of the effect what I mean.

https://www.youtube.com/watch?v=T3ja89l95Ts#t=1m45s

Any ideas on how to go about this?