Light



Lighting in Minecraft affects visibility, mob spawning, tree growth, and whether flowers and mushrooms will stay planted. Lighting can be provided by sunlight, torches, Jack 'o' Lantern, fire, lava, in-use furnaces, locked chests, Nether portals, redstone lamps, redstone repeaters, redstone comparators and certain other objects.

Effects of light
Keep in mind that light level is only one of the considerations that apply to mob spawning and plant growth. Refer to each mob's wiki page for more details.

Notes:
 * &Dagger; These restrictions only apply when spawning from a monster spawner, and not from a Silverfish block.
 * &dagger; Sunlight does not affect Snow and ice.
 * &dagger;&dagger; Applies to the light level of the block "above" the flowers, saplings, or seeds rather than the block they are planted in. Also, flowers, saplings, & crops will not uproot if exposed to direct moonlight.

Trivia:
 * The Halloween Update version Alpha 1.2.0 allowed monsters to spawn in higher light levels at lower depths, using the formula 16 - (Layer ÷ 8). At level 8 and below, mobs could spawn even in sunlight. Notch reverted mob spawning to the original method in version Alpha 1.2.1, saying, "it was way too annoying. I have plans on what to do with this."

Light-emitting blocks


The following values are the brightness of the block itself. The light emitted decreases by one for each square of distance from the light source. Glass does not diminish the light that passes through it, but water or ice reduces light that passes through it by 3 (2 for passing through +1 for normal block decrease). 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.

Light-filtering blocks


Solid blocks prevent the spread of light, while glass and portal interiors have no affect on light level.

All other transparent blocks reduce the spread of light. The following values are the amount each block decreases the light value. The light emitted decreases by one for each square of distance from the light source, more depending on the block it passes through.

Smooth lighting
Smooth lighting (which includes ambient occlusion as well as interpolating lighting across block faces) is the lighting engine added in Beta 1.3, with the help of MrMessiah. This lighting engine is set on by default, and can be enabled or disabled by accessing Video Options from the Options menu.

The engine blends lighting to add semi-realistic shadows and glowing from light sources. It darkens inside corners, resulting in small spaces appearing much darker. Before Beta 1.3, the feature could only be obtained by modifying the game with the help of MrMessiah's BetterLight mod.

In 1.5, a "Maximum" smooth lighting toggle was added, which fixes bugs with stairs. However, this is an optional toggle as it decreases performance slightly. The previous smooth lighting was put under a "Minimum" toggle.

History
Minecraft has an extensive history when it comes to lighting. Classic’s lighting model is simple and only checks whether a block is exposed to the sky. Indev’s model is more complex and considers a block’s distance from the nearest sunlight and from the nearest light-emitting block. Alpha’s model is a refinement of Indev’s, calculating sunlight and block-emitted light separately and using a different scale of light intensities. An earlier Beta update improved upon Alpha's model by adding the smooth lighting option, and in a later Beta update, the whole lighting engine was again rewritten to be much more efficient, have more detail, and be smooth in transition of lighting differentials.

Classic


In Classic, “sunlight” is emitted by the top edge of the map and will hit any block that is under it. It will pass through transparent blocks to light blocks underneath. Blocks that do not receive light are in a dim shadow that remains at the same level of brightness no matter how far they are from a light source.

Indev/Infdev
In Indev and Infdev versions there are 16 degrees of brightness, with a maximum of 15 for full daylight and a minimum of 0 for almost complete darkness. Brightness is a linear scale and represents its value divided by 15, so for example 15 is 100% ($15/15$) and 13 is 86.67% ($13/15$).

Each block that emits light has its own luminance value and the light value diminishes by one level each block from its source. If the neighbouring block already has a greater light value, it is ignored. The process is repeated for each block whose light value just changed.

During the day, sunlight has a maximum light value of 15. At dusk, it steadily decreases until it reaches a night-time minimum value of 4 representing moonlight. Sunlight is emitted by the top edge of the map, but does not diminish with distance from its “source”. A block lit by sunlight will be equally bright at any height or depth.

Minecraft - Pocket Edition currently features non-Smooth Lighting.

Alpha - Beta 1.2_02
Lighting in Alpha through pre-Beta 1.3 works as Indev and Infdev, except that the scale is different and is not linear.

Full daylight provides the maximum brightness of 15. Each value below this is 80% as bright as the one above it. For example, 14 is 80% as bright as sunlight, and 13 is 64% bright. This means that Level 0 still has 0.8¹⁵·100% = 3.5% of the maximum brightness.

Sunlight in Alpha has its own light array and a behind-the-scenes optimization to make dawn and dusk smoother: the amount of light from the sky is pre-calculated and saved along with the blocks, because it never needs to change except when blocks are added or removed. During dusk, nighttime, and dawn, a "darkness" value is subtracted from the sky to create the effects of different times of day.

In the Nether, light decreases by 10% each level, rather than the normal 20%. This means it will never be totally dark in the Nether. The minimum light value is 20.59%, providing a permanent dim ambience equivalent to normal world's level 8.

Beta 1.3 - Beta 1.7.3
Lighting from Beta 1.3 to 1.7.3 works the same as how it was in Alpha, but is greater optimized to allow smooth lighting.

Beta 1.8 - 1.4.7


In Beta 1.8, a new lighting engine was implemented. The new engine has added and changed the following:
 * The lighting of an area is influenced by the type of light source that is lighting the block: moonlight gives a blue tint, torches and lava give a reddish tint, and complete darkness and sunlight are the same as before.
 * Changes in lighting are now instant, and can be gradual as changes in the time of day and the state of rainfall now smoothly change the lighting value rather than individually updating the lighting of chunks one by one.
 * Using the new instant lighting, non-sunlight lighting now subtly flickers, although this feature is purely cosmetic and has no effect on gameplay.
 * Sunset is much more intense and realistic than before, and its intensity dims if the player turns away from it.
 * At extreme depths, black fog closes in. At the bedrock level, a torch can no longer be seen from 11 squares distance. This effect is inhibited by proximity to open sky (i.e. the degree to which the place where you are standing would be lit by sunlight), whether or not the sun is currently up. Digging a shaft from the surface down to your room will allow you to see far, even at bedrock level.
 * When inside the void, lighting operates similar to Classic, where objects in the void will remain at a constant brightness, regardless of how far they travel away from a light source, provided that they remain directly underneath an opening into the void. The brightness of the particular "column" of space is based on the current light level at level 0, the bottom bedrock layer. This applies to all entities, as well as particles.
 * Additionally, sitting in the void underneath a shaft which allows sunlight directly into it will remove the void fog, regardless to whether is it daytime or not.

1.5
As of 1.5, there were several lighting optimizations, including more realistic lighting and lighting interacting correctly with slabs and stairs. However, furnaces emitting light from all sides, and black spots in world generation were not fixed. As well, there are now three different levels of smooth lighting: Off, Minimum, and Maximum.

Future
In snapshot, Dinnerbone fixed black patches in world generation, and began overhauling the lighting systems such as changing the lighting of blocks to allow for directional lighting.

World generation issues were temporarily fixed, but Dinnerbone reverted these changes due to performance decreases. .

Trivia

 * Hostile mobs can spawn in areas where there should be light, but there isn't. This is because the game thinks there is a light level of 0.
 * Smooth Lighting is not apparent on the top of water or on paintings.
 * A 21 x 21 square of opaque material is enough to spawn mobs in the shadow underneath.
 * If Zombies or Skeletons are in water or in the low light levels caused by trees, they can survive through the daytime.