# Resistor on LED

I am conecting a green LED to 5V and I need to calculate resisitor value. Those are parameters from the datasheet:

• Vf=3.6-4V
• If=20mA.

According to Ohm's law: R=(Vi-Vf)/If, so when I change values I have R=1/0.02=50 ohms.

But it seems to me that this is too small. I read in several sites that the resistor shoul be 1k or at least 330 ohm. So I don't know which resistance is right.

• The maximum Vf for this LED is 20 mA. That doesn't mean you have to operate it at 20 mA. Jul 4, 2020 at 16:57
• Also 3.6V to 4V is exceptionally high for a green LED. It might be one of those new technologies. Typically, a green LED would have approximately 2V over it. So that might explain why you typically have seen larger resistors before for a green LED, but your LED might need lower. Jul 4, 2020 at 17:10
• @ThePhoton: That should be the max If, not Vf. The Vf the OP mentioned sounds very high for a green LED - he probably took values from the Absolute Maximum Rating table, rather than the more sensible operating values. Jul 4, 2020 at 17:11
• LEDs are not at all fussy about the operating current, as long as you don't exceed the Absolute Maximum rating. I've had some green LEDs that I had to run at under 1 mA to get the brightness down to an acceptable level for my use. Jul 4, 2020 at 17:13
• @cerouno Please provide a link to the actual data sheet. Jul 4, 2020 at 18:17