What is the difference between LED diode and Zener diode?

A diode is a semiconductor that conducts in a single direction only, whereas a zener diode conducts in both forward and reverse biased directions. 

Although both LEDs (light-emitting diodes) and Zener diodes are types of diodes, they have various uses and function differently:

1. LED (Light Emitting Diode):

LED is primarily used for emitting light when current passes through it in the forward direction.

It converts electrical energy into light energy.

LEDs are commonly used in lighting applications, indicator lights, displays, and various electronic devices where visible light emission is required.

LEDs have a forward voltage drop, typically around 1.5 to 3.5 volts depending on the color and type of LED.

2. Zener Diode:

A Zener diode is designed to operate in the reverse breakdown region, meaning it conducts when the reverse voltage applied across it reaches a specific threshold voltage known as the "Zener voltage."

It is used for voltage regulation and voltage reference purposes.

When the reverse voltage across a Zener diode exceeds its Zener voltage, it conducts heavily, limiting the voltage across it to its Zener voltage.

Zener diodes are commonly used in voltage regulation circuits, overvoltage protection circuits, and as voltage references in electronic circuits.

Zener diodes are typically characterized by their Zener voltage and their breakdown voltage tolerance.

In conclusion, both LED and Zener diodes are types of diodes; however, when reverse-biased, Zener diodes are utilized for voltage regulation and reference, whilst LEDs are primarily employed for light emission. They have varied roles in electronics, which is reflected in their different applications and working theories.