Simplest circuit to briefly (100ms) power a 1W LED?
Assume you have 20 digital outputs available to drive 20 LEDs
So each of them can be independently addressed
Since, only one LED is driven at a time you can have single constant current sink circuitry
It is like connecting anodes of all the LEDs to the VDD via MOSFETs separately but cathode of all LEDs, tie them together and connect them to constant current sink
One simple constant current sink is BJT with emitter resistor..current is set using (voltage at the base minus 0.7 ) / emitter resistor.
MOSFETs can act like switch to connect to the positive voltage while the BJT constant circuit will control the current for each LEDs..
Brightness will drop if two or more LEDs are turned on simultaneously