Glossary:Ballast

From Restarters Wiki

Whereas a conventional resistor only draws a current equal to the voltage divided by the resistance, in the case of a LED or a lamp utilising an electrical discharge through a gas or vapour (such as a florescent tube) the current increases rapidly once a certain voltage is reached. The current must therefore be limited by the circuit driving it. There are several ways this can be achieved but they are all referred to as a "ballast".