I'm gonna need some more details on what you're trying to do, and how you're thinking of implementing it.
Can you throw up a screenshot of a game with a similar effect?
- Are you trying for lightmaps (most likely?), or polygonal lighting?
Usually with lightmaps you just set the blending function to the correct one, and (IIRC) draw the light map on top of it. (IIRC) Or start with a full-screen black, draw your lightmaps onto it, and then merge that with the non-lit version at once. (Sorry, it's been years since I had to do this so my mind is a bit hazy.)
And you mention collision, and pixels. Are you making a TILE map game, or a PIXEL/bitmap game?
For lightmaps, you do the above, they're just "lit" bitmaps using known light patterns like a circle.
For polygonal lighting, you again draw to a "shadow buffer" or "light buffer" the size of your screen and merge in, but for "collisions" you're actually sending out rays from your light-sources and marking any spots they cover/hit.
There's tons of lighting tutorials for various game libraries on the internet. Try googling "light maps 2d tutorial." If you can identify the type of lighting you're looking for, we can drill down more into the details of how to implement it. But right now, there's "a thousand ways to skin a cat" so the best/easiest way to implement it depends on what specifically you're looking to implement.
Here's some example quick googles:
Here's polygonal: (and you can fuzz/blur it to make it look softer)
Here's a lightmap (just lightmaps):
Here's a lightmap:
Notice how the lights are all "the same." They don't have to be, you can vary size, intensity, etc. But the key here is they're not polygonal. They're not "rays" sent out from a lightsource that collide. Which means you can run into artifacts where they don't get clipped by walls (unless you specifically add that check).
But there are no hard-and-fast rules. Lightmaps can be made more "collision aware" and vertex lighting can be made more like lightmaps. Again, it really depends on what you're looking for.