reasonably doable: you won't get light within a steady beam, but an explosion that spawns a light and an emitter that makes it look like you're firing a beam of light at something
The problem is that moving the light quickly with a method like that (laser pointer style) will leave dots everywhere instead of an actual beam.
So, like the flashlights from Valve Games?
Could you post a screenshot of that?
I made a thread just like this a few weeks ago, but this needs to be made already. It doesn't need a beam, it just needs to light the spot that it is pointed at.