The data sheet for this LED gives the forward voltage range, at forward current of 20mA, of 2.8 to 3.8V. How can I choose a sensible current-limiting resistor value for this device, given such a wide range of possible forward voltages?
If I have a 5V supply and the forward voltage is 2.8V, I would need a 110-ohm resistor to give 20mA forward current (the rated value). But then if the forward voltage on a particular one was actually 3.8V, I'd only get about 11mA - and considerably less brightness. And of course operating from a 3.3V supply it's going to pretty random whether the thing switches on at all.
Am I misreading something?