Spawning. Slimes spawn in the Overworld in specific "slime chunks" below layer 40, regardless of light levels. They can also spawn in swamp biomes between layers 50 and 70 in light levels of 7 or less.

What light level can slimes spawn in?

Slime chunks can only be found below Y level 40 regardless of the light level, although they can naturally spawn in swamps between Y level 50 and 70 in light levels seven or less.

Do torches stop slimes from spawning?

Individual mobs (slimes or otherwise) can spawn in non-colliding blocks like torches and pressure plates, but entire packs cannot; the initial pack spawn requires an actual, empty air space.