It is not known whether the behaviors described in this page apply to Bedrock Edition as well, due to Bedrock's source code not being as easy to decompile as Java's.
A redstone signal (also known as redstone power) is a property common to all blocks in the game. Its value, known as signal strength, can range between 0 and 15 (inclusive).
Behavior
Redstone signals are directional, meaning that a redstone power source can have different signal strengths for each direction—certain redstone components emit a signal with a strength greater than 0 only for some directions. For the sake of simplicity, signal strength 0 is often referred to as the lack of a redstone signal.
The actual direction of a signal is inverted compared to the one that can be observed in-game: for example, the signal emitted by a redstone torch that's powering a piston above itself has the DOWN direction.[note 1] In the aforementioned example, the piston extends only if the direction it's facing doesn't match the direction of the signal.
There are two types of redstone signal: signal (conceptually similar to the community terms weak power or activation) and direct signal (conceptually similar to the community terms strong power or block powering). Most blocks use the default signal strength value of 0 for both signal and direct signal, however redstone power sources override this value, usually depending on the block's current state.
Signal
Signal is a type of redstone signal that powers the block adjacent to the power source for the specified direction.
Direct signal
Direct signal is a type of redstone signal that does not power the adjacent block for the specified direction, but instead powers the direct neighbors of that adjacent block, if it is conductive. The strength of direct signal is either always 0 (for blocks that lack direct signal) or matches the strength of the block's signal.
Misconceptions
Over the years, the redstone community has come up with various theoretical explanations that tackle certain redstone quirks. Unfortunately, these explanations do not always match what's actually happening in the game's code, therefore leading to some misconceptions.
Redstone dust power
Some players believe the reason why all other power sources can power redstone dust through conductive blocks but redstone dust itself cannot is due to the existence of two types of power: soft power and hard power. According to this logic, redstone dust emits soft power and every other power source emits hard power.
In reality, the cause of this phenomenon is that the strength of the emitted signal and direct signal of all redstone wires in the game is temporarily changed to 0 whenever any redstone wire is checking for power. This is controlled by the shouldSignal
boolean flag, which is then set back to true after the signal check.
Redstone dust can still be powered by other connected redstone wires even while the shouldSignal flag is set to false because it checks their POWER blockstate.
Emitted signals
A redstone power source that emits a direct signal with a strength greater than 0 for a given direction always also emits a signal with the same strength[note 2] for that same direction—otherwise, the power source wouldn't be able to power the block directly adjacent to it, but would instead only power the neighbors of said block.
This is different compared to the community's interpretation of redstone signals, according to which a redstone power source only emits one signal type per direction.
Unusual signal strengths
Use at your own risk.
At the bottom: a comparator reading a hopper with signal strength 15.
Signal strength can technically be any non-fractional number between -2147483648 and 2147483647 (inclusive), due to it being a signed 32-bit integer. All redstone components are however limited to the 0-15 range, excluding comparators. A comparator that reads the items from a container can output a signal outside of the usual range if the container in question has negative item stacks (signal strength below 0) or stacked unstackable items (signal strength above 15) inside of it. Such items can be obtained with the use of bugs, which might or might not have been patched depending on the game's version.
When a comparator that has an unusual signal strength interacts with any powerable component excluding other comparators, that component will reset it to either 0 (if it's less than 0) or 15 (if it's greater than 15). For example, using a comparator with signal strength 20 to power a piece of redstone dust causes the latter to emit a signal with a strength of 15.
