A semiconductor light-emitting diode (LED) is a device that produces light when electric current passes through semiconductor material. LEDs became common in modern displays because they are compact, efficient, durable, and can be controlled electronically to form segments, symbols, or pixels. They replaced or supplemented older display technologies such as Nixie tubes and vacuum fluorescent displays.
In cyber security, LEDs are not a security mechanism by themselves, but they can provide useful physical status indicators on computers, network equipment, and embedded devices. Attackers may exploit poorly designed indicators or connected display systems to mislead users, while defenders can use device lights as one clue when checking power, activity, or network status. Because indicators can be disabled, altered, or absent, they should not be treated as definitive evidence of a device’s state.