Mob Spawning Light Level

/gamerule mobSpawningLightLevel 0

Mobs can only spawn at light level 0

/gamerule mobSpawningLightLevel 15

Mobs can spawn at any light level

/gamerule mobSpawningLightLevel 7

Mobs can spawn at light level 7 and below (same as normal)

/gamerule mobSpawningLightLevel 10

Mobs can spawn at light level 10 and below