"Ideal" Solid State Switches?
One way is to use a comparator to compare the input against a 3.3 Volt reference. 

The output of the comparator can be used to drive a BJT or MOSFET to provide the requisite current gain - or the LED can be driven directly by the comparator if a suitably high output current comparator is used. 







simulate this circuit &ndash; Schematic created using CircuitLab

Note that comparators often have a current sink output, so a pull-up resistor would be needed at the comparator output for this to work... but that is getting into specifics.