A device used in some instruments to display numerical and alphabetical characters. It consists of an array of light-emitting diodes, LEDs, which are semiconductor diodes that emit light when a forward bias is applied. LEDs are small, cheap, and have relatively low current and voltage requirements and long life. Their power consumption is, however, significantly higher than that of LCDs. In an LED display these diodes are arranged in such a way that by selectively illuminating individual ones in the array, simple characters are formed on the display. Seven diodes suffice to display the digits and some letters.

Single LEDs are used almost universally where single on/off indicators are needed. Most colours are now available and high efficiency diodes are replacing incandescent lamps in some applications.