How to power a low voltage LED with a high voltage source?
You just need to put a resistor from the 28V in series with the LED unit. The LED drops 2.2V at 30mA. So this added resistor needs to drop (28 - 2.2V) = 25.8V. 

A further calculation needs to be made based upon the current you want through the LED. Lets say you want it really bright so choose the full 30mA rating of the LED. Ohms law tells us that the resistor value (R) will be 25.8V / 0.030A = 860 ohms. You could pick a standard value resistor like 910 ohms or even 1K ohms but the current through the LED will be slightly less. The 1K ohm resistor would result in about 25.8mA through the LED. This current level is still probably way more than you need for a panel indicator. Even 10mA is often more than needed. So a resistor with a 3.3K standard value would allow a current of 7.6mA. This size resistor has a nice advantage in that it would only need to be a 1/4 watt rating instead of the other smaller values that would need to have much higher wattage rating. 

Using the 28V rated LED unit is just going to be an indicator with an already integrated resistor inside that does the same thing as if you add one yourself.