When Driving An Indicator L.E.D.

[tumbleweed]

I'm pulsing the IR L.E.D. in a Solid State relay (see link) and would love to avoid translating through a mosfet down to the nominal forward voltage of the L.E.D. shown in the data sheet. Pulses are from 1 to 40 milliseconds long. All of supply is a regulated 5 volts. Can I skip the translation voltage?

Once you figure out how an LED works, then you can skip any additional circuitry you have driving the MOSFET relay LED input, and just treat it like a normal LED.
All you need is a resistor in series with the input LED. According to the datasheet you want a min of 3mA to turn it on, so to be safe calculate R so that you get 5mA,
something like R=(5V-Vf)/0.005, where Vf is the LED forward voltage taken from the datasheet.