Dirt On Camera (BF3 and Metro Last Light)

that top picture isnt really a good pic. it's been touched up far too much to be a realistic picture of game graphics.

as for the bottom one a simple way to get that affect is to have a particle system near a light source spawn particle with very high reflection/specular light values.

I don't think that second one is light reflecting off the camera, it's light reflecting off dust particles actually spawned in game.

a lot of that lighting is just well done lighting code. The large halo's are just accurate reflections of light reflecting off objects projected onto the wall. That's not faked or anything they actually calculated light reflections.

If you want good quality lighting and you don't know much about lighting i'd honestly suggest you check the asset store. For high quality lighting it's probably easiest just to pay.