i am trying to understand basic electronics so i don't need to only copy projects i see on the internet, but also be able to create my own.
So, my problem is that i am trying to figure out how to find the right Resistor to use with LEDs.
I know about the Ohm's Law: V=IR and i though i should be able to use it to find the R value.
But my problem is that i have the LEDs for reaaaaaaally long time and i have no idea about any of it's values.
I have read often that a average LED takes about 20mA current.
So it would make something like:
V = I R
R = V / I
R = 5 / 0.020
R = 250 Ohm
But what if i don't know the I from the LED, how can i find that out?
Also, i read about this formula for calculating the Resistor for a LED:
R = (Es - Eled) / Iled
Es - source voltage (V)
Eled - voltage drop across the LED (V),
Iled - current through the LED (A)
Would it be better to use this formula?