LED stands for Light Emitting Diode.

An LED is a semiconductor device. In more technical terms, it is a PN junction diode which emits light when an electrical current flows across.

Although the LED was invented in 1962, it is not until 1968 that it has been commercially available.  The first visible LED was only available in red. Yellow, orange and green followed in the 70s but did not catch on on popularity until years later.

In the 70s, we saw red LED displays appear on household devices such as watches and calculators.

The original package for LEDs was a round casing with a dome shaped top, in either 5mm or 3mm diameter. These packages, still widely in use today, are called T1-3/4 (5mm) and T1 (3mm). The dome shaped top acts as a magnifier lens and the material as a diffuser.

Multi LED packages appeared at the end of the 70s, arranged in bar graphs in which individual LEDs were visible or light bars in which several LEDs were placed in a larger, diffused package.

It took more than two decades to see other LED colors, with the first blue LED in 1994. Research and development of the blue LED was motivated in part by its possible application in television displays, as it would allow covering the whole visible spectrum by combining blue with red and green.

White LEDs followed shortly after blue, but not by combining all colors. Instead, white has been achieved by an application of phosphor coating on blue LEDs.

The industry has come a long way since the original red LED. I still remember when the first LED calculator entered our house in 1975.