@fungus
Please keep things in perspective.
those strips can draw a LOT of amps - a 5m strip with 60 LEDs/m and all the LEDs turned on needs over 18 amps.
Well durr! My grandmother can suck eggs as well. Well are discussing the techniques by which this can be done we are not talking about a universal solution. Why stop at 18A?
A 2R2 resistor at 18 amps will drop 40 volts
You know what, I can do ohms law as well.