OverviewThere are 16 levels of light, the highest being produced by Sunlight. Light is decreased (or blocked entirely) when a block is situated in front of a light source. The block which decreases light the most is the base of a piston. The light level of a block affects whether or not certain Hostile Mobs will spawn on it.
Levels of Light
The light level determines if hostile or passive mobs will spawn. For example, a Cow will spawn in light level 7 or higher on Grass blocks. This is also the case for Pigs, Chickens and Sheep. Hostile mobs, such as Skeletons and Zombies, will spawn in light levels 7 or lower. A player can keep Hostile mob from spawning in an area by lighting up the area with torches or other light-emitting objects.
List of light levels in Minecraft:
13: Active Furnace
12: Sunlight (during rain or snowfall), Glowing Obsidian (Pocket Edition only)
11: Nether Portal blocks
9: Redstone Ore (when touched)
8: Sunlight (during thunderstorms), Ender Chests
7: Active Redstone Torches
Smooth lighting is the lighting engine added in Beta 1.3. This lighting engine is on by default (it is always on in Minecraft: Pocket Edition), and can be set to maximum, minimum or off by accessing Video Options from the Options menu.
The engine blends lighting to add semi-realistic shadows and glow from light sources. It darkens inside corners, resulting in small spaces appearing much darker. Before Beta 1.3, the feature could be only obtained by modifying the game with the help of MrMessiah's BetterLife Mod.
The "maximum" smooth lighting toggle fixes bugs with stairs. However, this is an optional toggle. The "minimum performance" does not fix the bug.
Minecraft has been evolving over time, and the lighting system itself has changed along with it.
Smooth Lighting didn't exist in Minecraft Classic. Instead, light spread on dim-lit areas. "Sunlight" was emitted by the top edge of the map and would hit any block that was under it. It would pass through transparent blocks to light blocks underneath. Blocks that did not receive light were in a dim shadow that remained at the same level of brightness, no matter how far the block was from a light source.
Alpha - Beta 1.2_02'
Lighting in Alpha through pre-Beta 1.3 worked similar to Indev and Infdev, except the light scale was not linear.
Beta 1.3 - Beta 1.7.3
Lighting from Beta 1.3 to Beta 1.7.3 worked the same as it was in Alpha, but was optimized to allow smooth lighting".
Black patches in world generation and structure generation were fixed in update 1.7.2.