In LEDs (light-emitting diodes), the production of light takes place in a semiconductor crystal which is electrically excited to emit light. When a current is passed through the solid crystal, it induces electroluminescence. A housing protects the semiconductor from environmental conditions.

LEDs produce monochromatic radiation. The colour tone of LED light is defined by the dominant wavelength. LEDs come in the colours red, orange, yellow, green and blue. White light is produced either by mixing the three RGB colours (red, green blue) or by applying the same conversion principle found in fluorescent lamps. Here, the light of a blue LED excites luminescent material, changing part of the blue light into yellow. Overlaying the non-absorbed blue light with the yellow light emitted produces white light.

LEDs are extremely efficient: the luminous efficacy of white LEDs is already up to 250 lumens per watt (lm/W). The intensity of LED light declines very slowly (degradation), sudden failure is rare. The life of an LED – which is very long at over 100,000 operating hours – is defined by the degradation time to 50% of the original luminous flux. Excessively high operating or ambient temperatures shorten an LED's life considerably.