Redstone Torch

A redstone torch is special block in Minecraft that interacts with Redstone. It in itself has several functions in redstone circuitry, but (arguably) one primary purpose: to power redstone.

As a light source
Using a redstone torch as a source of light is not recommended because it has just half the light output of a regular (coal) torch. Redstone torches will not melt ice or snow due to their low light level (7), and will not prevent mobs from spawning (though one will decrease the probability of a mob spawning). 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. However, placing a redstone torch can be a good indication of whether there is adequate lighting on a block to prevent mobs from spawning since it has a light level of 7, the maximum light in which mobs will spawn, or you could use it while spawner farming when you need light to see but not too much for the mob to stop spawning.

As a redstone circuit component
A redstone torch can provide a power source for wires. This is their primary function. 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 typically happens 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 apply a current to itself thus turning it off and removing current allowing the torch to come back on and once again apply current to itself. This will cause 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.

Redstone torches can also burn out if one clicks a lever quickly and repeatedly with the lever being hooked up to a redstone torch or leads a wire from the torch, up one block, and reconnects it to the torch.

Bugs

 * When trying to make an RS-NOR Latch or other redstone circuits, sometimes the redstone torches burn out unexpectedly.
 * If you have a redstone torch on top of a block and powered redstone dust powering the block that the torch is attached to, the torch will not turn off as it should, this seems to depend on the coordinates of the torch. Place the torch somewhere else and it may fix the problem. If the problem persists move the torch to another location, or replace the redstone dust powering the block with a repeater.
 * If you burn out a redstone torch by rapid use and try to replace it, it will instantly burn out again when powered
 * In Beta 1.8 the redstone torch will not be turned off if power from redstone dust flows through it. Other power sources (like levers) will still turn them off though IF directly powering the torch.
 * In 1.2.3-current, placing a redstone torch (happens with torches/is more noticeable with torches) hanging on a wall that is surrounded everywhere but the bottom will still light up what is beneath it, however the block itself will not be lit.

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:

or one could use an inverter which reverses the charge but still extends the signal.