I am direly confused on this. I've used 220 Ohm resistors in the past for all of my LEDs (at least that I can remember), however nothing on my arduino+breadboard with a few leds on the 5V breadboard rail had worked.
I finally looked at the data sheet for the LEDs from the overseas place I ordered them from, and they seemed to require 35mA or so rather than 25.
I calculated that to be ~80 Ohms (5V-2V(drop) = 3V / 0.035A) = ~85 Ohm.
This explained perfectly why they had not started working, so I pulled out a 100 Ohm (which read out to about 95 with a multimetre) and set it up.
Now the LED did not light, to my surprise, feeling the resistor which was just out of curiosity felt sharply cold - of course realizing that it is so hot it overloaded the nerve endings on my fingers being too hot to touch.
My rough calculations were:
3V / 95 = ~35mA, and 3V? * 0.035A = .105W, seemingly not enough to cause much heat at all, especially over 3-5 seconds and being rated for ~.25W
Can you understand what I am doing wrong, or what could be going wrong?
My circuit is just 5V pin -> breadboard -> 100Ohm resistor -> LED -> Ground pin.
I just cannot make sense of it.
edit: I very recently shorted an LED without a resistor from 5v->gnd, possibly damaged something..