Minecraft wiki entry for Night_Vision, associated text: Night vision greatly increases the brightness, so the player can easily see in a light level of 0. However, it is not as bright as a light level of 15 (e.g. with the "Moody" brightness setting, it is similar to block light level 12–13 and no sky light in the overworld within the "Bright" brightness setting), and as such the player can distinguish between light levels.