Few parts are as ubiquitous as light-emitting diodes: the lack of classic light bulbs means they get pressed into usage as indicators, even in basic electronics tutorials. This article looks at them in more detail and focuses on less common applications and pitfalls in LED usage.

Physics: How LEDs work and how their spectra look

Even though this text focuses on practical applications, a small excursus into semiconductor physics is justified. A light-emitting diode is a diode that is doted with specific chemicals. These ensure that the excess energy in forward conduction is – partially – emitted as visible or infrared / UV light. Depending on the chemical used for doting, different colors are achieved. Unlike a regular diode, however, LEDs are not well suited to rectification applications – their forward voltage is high, while the reverse breakdown occurs very early.

Initially, manufacturers provided red, green, and yellow LEDs. Blue LEDs have been available for about ten years, with pink and purple LEDs being relatively new constructions (see, e.g., the unboxing video at https://www.youtube.com/watch?v=tFjaeYsQ2vs). Sadly, purple LEDs sometimes yield rather unsatisfactory (read: blueish) colors.