Efficient method to farm souls of light/night?

What I did was to build an artificial meteor biome using 50 blocks of meteor ore inside the underground corruption and hallow. By the time you have reached hard mode you should be able to one hit kill the meteor heads. Within 10 minutes in each biome I was able to get all the light/dark souls I'd need to make every end game item. I've not yet tried using statues and a lava film to farm souls, but considering that spawned mobs don't drop cash I suspect it possibly won't work. However, a corrupt bunny/fish spawner placed inside of the underground hallow/corruption should work just fine, netting you both the massive cash and a ton of souls.

I recommend fighting either King Slime in Hallow worlds, or the respective evil bosses, in Crimson or Corruption worlds. This is what I did, and I found it to worked great!

The reason I don't fight King Slime in both biomes is because he can be annoying to spawn, whereas the evil bosses are very easy to summon.

You can sell the crimtane/demonite for easy gold.