Light

Light (or lighting) in Minecraft affects visibility, mob spawning, and plant growth. There are two types of light: sky light, which is provided by the sun, and block light.

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. Light is completely monochromatic and cannot be truly colored.

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 toward 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, 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 toward 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. In other words, 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 directions is 13 while the diagonal blocks in all four directions has 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. Light is also able to spread along complex, twisting paths if blocked by opaque blocks, using a kind of flood fill algorithm.

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 away (i.e.- not touching the wall) has 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 Blocks
Light blocks have an associated value between 0 and 15 inclusive. When placed as a block, they produce this light level.

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 iron bars 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. This means that below these blocks, the sky light level decreases by 1 for each block of distance downward, starting at the obstruction. In Java Edition, water has the same effect. This effect can be clearly seen by creating an opaque 1×1 chimney with leaves or a cobweb at its opening at the top.

The following values are the amount by which 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 it passes through.

Mobs also cast circular/tridecagonal shadows; however, these are unrelated to the light level.

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 (including 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. It affects only how the world is rendered on the screen, not how blocks calculate their light level, so it has no effect on mob spawning or crop growth. It is set on by default. Paintings and water are unaffected.

$$, smooth lighting can be turned on or off in the Video settings, accessed from the Settings menu. $$, it has three settings: minimum, maximum, or off, and can be changed 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.