Day 1 - false start
I was going to create a dual-stick shooter in a dark cave where the only light is the light from projectiles. I got a functionally working prototype [youtube link] wrt lighting effects. Unfortunately, despite the smooth appearance, it's actually dropping FPS and there's only a few bullets on the screen and so it's not particularly viable. It seems the pygame blend modes are great for either one-time-then-cached image modifications or blitting small areas. But having a "shadow layer" that you blit light away from with gradient images...well...I'm not sure what I expected, performance-wise.
I'm going to go down to the next item on my ideas list and start over today.