LEDs typically require 10 to 20mA, the datasheet for the LED will detail this along with the forward voltage drop.
For example an ultra bright blue LED with a 9V battery has a forward voltage of 3.2V and typical current of 20mA.
R = (9 - 3.2) / 0.02 = 290 Ohms
Fuente: http://www.kitronik.co.uk/news-info/what-resistor-should-i-use-with-my-led
Led azul: máximo 3v
Voltaje para Leds ultrabrillo
Led rojo: máximo 2vLed azul: máximo 3v
