The amount of light this block will emit in a range of 0-15. Higher value means more light will be emitted. Reference values: torch (14), glowstone (15), redstone torch (7), soul torch (10). Monsters cannot spawn on blocks with light level 8 or higher.
Alternate Simple Representations
This item can also be represented as a Integer number.
Samples
Block Fabricator
"minecraft:light_emission": 7
Block Gray Ore
"minecraft:light_emission": 15