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.



In the Overworld and the End, the brightness of a block decreases by 20% per light level. Note that this is an exponential decrease, so light level 13, for example, represents 64%, rather than 60%, of the maximum brightness. A light level of 0 corresponds to a brightness of 3.52%.

In the Nether, the brightness decreases by 10% per light level. For example, a light level of 13 equates to a brightness of 81%. A light level of 0 represents a brightness of 20.59%, approximately light level 8 in the Overworld, providing a permanent dim ambiance within the dimension.

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.