Redstone Torch

A redstone torch is special block in Minecraft that interacts with Redstone. It has several functions in redstone circuitry, but the primary purpose is to act as a power source.

As a light source
Redstone torches have a light level of 7 and will not melt ice or snow due to their low light level. This means they have half the light output of a regular torch, allowing mobs to spawn nearby.

Placing a redstone torch can be a good indication of whether there is adequate lighting on a block to prevent mobs from spawning. Redstone torches have the maximum light in which mobs will spawn, so they can be helpful when spawner farming.

Although one redstone ore block will produce 4-5 redstone dust, redstone is much harder to find than coal, and is made into torches at a 1:1 ratio (rather than 1:4). Therefore, using redstone torches as light sources is merely a cosmetic application and little else; unless you happen to have more redstone than desired.

As a redstone circuit component
The primary function of a redstone torch is to provide a power source for wires and circuits. Wires in turn are used to operate doors, pistons or switches from a distance. The torch can power the wire for a length of 15 blocks, and takes 1 "redstone tick" (2 game ticks) in Minecraft world time (approximately 0.1 seconds) for power to flow through it.

If redstone is scarce, and the only purpose of the torch is to supply power (i.e. not being used in any logic gate), it can usually be replaced with a lever, with the added advantage of being turned off if the need arises.

The redstone torch will constantly power a set of wires while placed, and is used as a "block-based" switch sometimes. It acts as an inverter, or NOT-gate (and is labeled as such in the game's source code), in redstone circuits, and turns off when any adjacent switch, lever, wire or pressure plate is turned on. See Redstone circuits for more information on using redstone torches in circuits and logic gates.

Redstone torches can be used to sabotage/activate traps and mechanisms as well as opening locked iron doors making it useful for raiding parties in multiplayer. A door circuit designed to be closed when constantly powered prevents this vulnerability.

Redstone torches will burn out when switched between the on and off states too often (8 or more off-on-cycles within 100 ticks or approximately 5 seconds). This can happen if the player clicks a lever quickly and repeatedly with the lever being hooked up to a redstone torch, or when the player creates an infinite feedback loop by inadvertently or purposely wiring a redstone torch back into itself (a one clock). This will cause the torch to repeatedly apply and remove current, allowing the torch to come back on and once again apply current to itself. This causes the torch and any mechanisms wired to it to rapidly activate and deactivate repeatedly and could crash the game depending on the complexity of the mechanism.

This is likely why Notch programmed the torches to burn out. When burnt out the torch will issue a puff of smoke and a hiss similar to an extinguished fire. Then it will ignore any events which would normally turn on the torch until enough time has been elapsed so that there are 7 or less off-on-cycles within the last 100 world ticks. After that a new event of unpowering the blocks adjacent to the torch is necessary to turn it on again (current state of the blocks is ignored, it requires a new on-off-edge or a general kind of block update). There is no limit how often a single redstone torch can burn out.

Trivia

 * In the source code, redstone torch is called.
 * The redstone torch has the same placement rules as the regular torch, as seen by this chart.
 * Before redstone repeaters were added, redstone torches were used to extend signals like this:

where the 2nd Torch (the torch further to the right) is attached to the adjacent block.


 * Alternatively, one could use a double inverter, which uses exactly the same amounts of materials as the above method, but can be used in a one block high space (at the cost of being 2 blocks longer):

where both torches are connected to their adjacent blocks.