Driving a 5V LED on computer chassis with 3.3V
What they're saying is the '5V LED' has internal resistor. Your card also has a resistor (220 ohms). So what will happen is that the LED will be very dim since it will be running on 3.3V -&gt; 220 ohm -&gt; LED dropping resistor in series.
If you can modify the LED to short out the resistor it could work, or replace it with a plain (non-resistor) LED.