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.

Why are slimes not spawning in my slime chunk?

Slimes are shy - they won't spawn if other mobs are nearby. Assuming your area is in the correct zone (inside a Slime spawn chunk and within ~40 blocks from bedrock), you also need to check the ravine nearby and light it with torches to keep other mobs from spawning nearby and stopping the Slimes from spawning.

Do torches prevent 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.