Hi Kyrill,
Excellent calculator; thanks for sharing it!
Pretty straightforward stuff: deduct 2V from the rail voltage, pick the current desired (3mA for a green or red LED, 0.2mA for a HE blue LED), divide the mA into the deducted dropped voltage (in this case 48V for a 50V 100W AKSA rail) to get the kilohms of the dropper resistor.
Cheers,
Hugh