Light

Light (or lighting) in Minecraft affects visibility, mob spawning, and plant growth.

Brightness


There are 16 light levels, which are specified by an integer from 0 (the minimum) to 15 (the maximum). The game uses the light level of a block to compute the brightness of a given block.

The brightness of a block depends on both the level of light from other blocks and the level of sky light. Note "sky light" here is not reduced at night, instead the brightness curve itself changes based on the time. In this it matches the sky lighting value on the debug screen.

In general, lighting due to blocks results in a higher brightness, which is balanced by the fact that light due to blocks effectively starts at 14 (solid light-source blocks emit a level of 15, but that's for the light source block itself) while sky-light brightness is 15 outdoors. Light due to blocks also tends towards orange in the middle ranges, while sky light in the Overworld daytime is white.

In the Overworld with the "Moody" brightness setting, full daylight reaches 98% brightness, while at night brightness is reduced to about 17% and is shaded blue. Full darkness is about 5% brightness.

In the Nether, sky lighting doesn't play a role since there is no source of sky light (although if there were, it would reach about 99% brightness). Full darkness with the "Moody" brightness setting is at about 25% brightness, which is only slightly darker than a block light level of 7 and no sky light in the Overworld, and is shaded orange like block light.

In the End, sky lighting wouldn't play a role even if there were a source of sky light; this can also be seen if lightning is summoned in the End, there is no flash of brightness like there is in other dimensions. Full darkness in the End with the "Moody" brightness setting is about 28% brightness, and is shaded towards a bluish-green rather than the orange of the Nether and of block lighting.

Spread
The light from light-emitting blocks decreases by one light-level for each meter (block) of distance from the light source. Note that this applies to each of the 3 axes including N/S, E/W, and up/down. This fact is significant for preventing hostile mob spawning. If a torch (level 14) is placed on a wall two blocks up from the floor, the light level on the floor one block away from the wall will be 11 (e.g. 14 minus 2 down, minus 1 south). If the torch were placed on the floor at floor level, then the light level on the floor one block away from the wall will be 13 (e.g. 14 minus 0 down, minus 1 south).

Light decreases diagonally by "taxicab distance", or the sum of the distance along each axis. This means that if a torch (level 14) is placed on the floor, the light level on the adjacent floor blocks in all four direction will be 13 while the diagonal blocks in all four directions will have light level 12 (e.g. 14 minus 1 south, minus 1 east). Along a floor, this effect produces a diamond-shaped pattern of illumination around the light source. Remember, light decrease takes place in three dimensions. This means that if a torch (level 14) is placed on a wall one block up from the floor, then the block on the floor that is diagonally one block way will have a light level of 11 (e.g. 14 minus 1 south, minus 1 east, minus 1 down).

Blocks
The following values are the brightness of the block itself:

Light-filtering blocks


Opaque blocks prevent the spread of light; a 21×21 square of opaque material is enough to spawn mobs in the shadow underneath. By contrast, some transparent blocks such as glass and portal interiors have no effect on light level. All other transparent blocks reduce the spread of light.

Leaves and cobwebs do not have any extra effect on block light, but they do diffuse sky light. The light level from sunlight or moonlight is the same in each block of air in the column of air above the highest obstruction in the column. When placed, leaves and cobwebs obstruct that light column so that the lowest air block above the leaves acts as other light sources do. As you descend below the leaves, the light level diminishes with distance like it would from other light sources such as torches. To control this effect, create an opaque 1×1 chimney with leaves at its opening above you.

The following values are the amount each block decreases the light value. The light emitted decreases by one for each block of distance from the light source, more depending on the block through which it passes.

Effects of light
Note: Keep in mind that light level is only one of the considerations that apply to mob spawning and plant growth.

Smooth lighting


Smooth lighting (which includes ambient occlusion as well as interpolating lighting across block faces) is a lighting engine that blends light levels and darkens corners to add semi-realistic shadows and glowing from light sources.

This lighting engine is set on by default, and can be set to minimum, maximum, or off by accessing Video Options from the Options menu.

Trivia

 * In Minecraft's source code, the luminescences are defined using the floating point values in the third column. In a weird quirk, these floating point numbers are fractions of 16, but are multiplied by 15 to get the integer light value.
 * This means that both 0/16 and 1/16 (0.0 and 0.0625) correspond to the integer light value 0.