Some variations of the basic diode are:

the Zener diode which doesn't conduct unless the voltage is over a threshold, written Vz. The Zener effect, for which this diode is named, was discovered by Clarence Melvin Zener, in 1915.

The Light Emitting Diode, or LED. All diode radiate energy from the P-N junction, LEDs are made to make that light visible. LEDs are the little lights on your computer, or monitor.