Minecraft wiki entry for Overworld, associated text: During the daytime, the sun acts as a powerful light source, with a light level of 15, the maximum. Sunlight is strong enough to grow plants and affect the way mobs spawn, among other interesting effects. During the nighttime, the moon is the only natural light source. However, moonlight is comparatively dim; the light level falls to a minimum of 4, allowing hostile mobs to spawn. Other than during thunderstorms, nighttime is the only time players may sleep in a bed.