Light Level

The light level condition checks the block light level or skylight level. This means we can check if mobs are spawning in an area.

Argument	Description	Default Value
min	The minimum light level	0
max	The maximum light level	15
mode	Either BLOCK, SKY, or BOTH (see below for info)	BOTH

Mobs can spawn at light level 7 and below

BLOCK

BLOCK only checks light from light sources, such as glowstone, torches, lava, etc.

SKY

SKY only checks the exposure to the sun. This means that your light level will be low if you are underground or under a ceiling.

BOTH

BOTH checks both BLOCK and SKY and uses whichever value is bigger. This is what Minecraft does to check if mobs can spawn.