help with resistor

[mikesibe1]

I'm going to use 100 5mm 20 ma red leds. My battery is 5 volts. Which resistor would I need

[Silver Serpent]

Insufficient information for a meaningful answer.

More importantly, we need to know the forward voltage of your LEDs, and how you intend to wire the LEDs together.

You *will* need to make segments, otherwise 100 LEDs in series, at an estimated 2v forward voltage, would require a 200v power supply. Wiring them all in parallel would require 2A of current, which is far more reasonable. But one long chain will give you bright LEDs at one end of the chain, and dim LEDs at the other.

http://forums.thecustomsabershop.com/showthread.php?17109-Tutorial-FJK-s-quot-Down-and-Dirty-quot-guide-to-Ohm-s-Law will teach you how to calculate a resistor value.

As an aside, I've never heard of a 5v battery. What kind are you using?