The LED

LED - Stand for Light emitting diode.

They have two contacts the Anode(+) and the Cathode(-)

A diode in electronics, can be compared to a one way valve in a water system.

When current flows through the led, (+/- 10 to 20 milli-amp) The arc is seen through the lens of the LED.

An LED, like most diodes, requires at least 0.6 Volts for current to pass through it

The Legs of the LED is in different length the Annode ( or positive leg ) is slightly longer than the Cathode (negative leg).

The negative side of the Led is flattened on the rim of the lens to allow to to determine which side is which , if the legs is already cut shorter.