L star LEDS. Why is the Resistor needed?

[Ripper]

On my sabers, on a straight connection and on a Hasbro O-B-1 board I used no resistor. Because when I did, it just dimmed the heck out of the LED. And on all the diagrams I looked at, they never say the ohm or v needed. But with no resistor I get a bright light. I used the diagram from cardcollector's tread. The 3.7 - 6V set up with no recharge port. I needed no port cause the batteries come right the bottom of the saber. I'm using a 3.7 V 18500 Li bat. So I'm guessing if I go higher with my voltage on the power. Like two 14500's I may need one. Am I right or what. Some help please masta, I know not what I do!

[Azmaria Dei]

without knowing which LED you're using, i can't help much - but if you're using an LED rated for 3.4V or more, you can leave the resistor out without a problem most of the time. and if it's working for you as it is right now, just stick with it. you'll probably reduce the lifetime of the LED to around 35-45 years, but i'm guessing you'll be happy with it lasting that long as well as the brightness.

[Ripper]

I have three colors; Red, cyan and green Luxeon Rebel stars. The red is straight to the power. The Cyan has a hasbro board and the green has a Luke ROTJ board. all but the luke run on a 3.7 v bat. The luke has the original batteries.