Originally Posted by
PdalPowr
I have been told a resistor is necessary but not told why.
The lighting circuits I have built without resistors seemed to work well.
As in most builds they get built better if we know what goes where and why.
as hinted by the other answers, the circuit needs to limit the amount of current that can flow through the LED.
Sometimes this is done with a resistor.
Other times, a regulator circuit is used.
Still other times, the designer used a battery that can't provide much current, or whose voltage is barely sufficient to get the LED to conduct.
The literal answer to your question is "no, a resistor is not always required", but the general idea of needing to limit the current is quite true.
Steve in Peoria