but since people say datasheets tend to be wrong, I'm aiming at 900mA.
Note 1: Pulse width ?100?s, repetitive frequency = 100 Hz
Since the arduino pin supplies 20mA, that means I'll need a resistance of around 172ohms. Correct?
However, the whole concept of driving the LED so hard is wrong, what are you doing with the LED that needs driving it for so short a duty cycle and as hard as this?