A Short History of LEDs
Early red LEDs were dim indicators; efficiency has grown enormously since.
First glimmers
In 1907 the engineer H. J. Round noticed a faint glow from a crystal of silicon carbide when current passed through it. In the 1920s Oleg Losev studied the effect more closely, but the light was too weak to be useful.
The first practical LED
In 1962 Nick Holonyak Jr. made the first visible-light LED, a dim red one. Red indicators appeared in calculators and equipment through the late 1960s and 1970s, followed by green and yellow.
The blue breakthrough
Blue was hard to make efficiently. In the early 1990s Isamu Akasaki, Hiroshi Amano and Shuji Nakamura produced bright blue LEDs, work recognised with the 2014 Nobel Prize in Physics.
White light follows
Putting a phosphor over a blue chip gave white LEDs in the mid-1990s. Improvements in efficiency and falling prices then made LED room lighting, screens and headlamps common.
Try it yourself
Sketch the circuit on paper first, calculate the values, then build it on a solderless breadboard using a low-voltage supply. Measure with a multimeter before you make anything permanent.