History of LED (Light Emitting Diode)#

LEDs are used everywhere in the world today — for lighting, displays, and signaling.
Let’s take a look at how the LED was born, refined, and developed.

1907 — “Wait… it just glowed. What was that?”#

1907, in a laboratory in England.
Henry Joseph Round, a radio communication engineer, noticed a strange phenomenon when he passed an electric current through a silicon carbide (SiC) crystal.
“Whoa! It’s giving off light at the contact point!”
Round reported the phenomenon in the journal Electrical World.
But at the time, no one imagined that this faint glow would one day replace the lighting of the world.
The light was simply too weak to seem useful.
And so the seed of the LED was quietly buried.

How Does an LED Control Its Brightness?#

Take a close look at Christmas tree lights. The lights don’t just turn on and off — they gradually get brighter and then gradually dimmer. In other words, the brightness is being controlled.

Is the LED’s brightness really being controlled? No! In fact, it’s tricking our eyes into thinking the LED’s brightness is being adjusted. Let me explain the principle.

A Simple LED Circuit#

I’ve prepared a battery, an LED, and a switch. By connecting them in series, I built a simple electrical circuit. As shown in the figure on the right, when the switch is closed, current flows and the LED turns on. Conversely, as shown on the left, when the switch is opened and the current is cut off, the LED turns off.