A LED might need 30mA and lets try a couple voltages.
With a 9V battery (9v-2.1v) / .030A = 230 Ohms
With 220V supply (220V - 2.1) / .030A = ~7.3M Ohms
The 7.3 Ohm resister is @ 6.5 Watts
The 230 Ohm resister is @ 207 mW
So what about the LED? What is the different wattage? What if I did 1 million volts? What governs the max voltage?
With a 9V battery (9v-2.1v) / .030A = 230 Ohms
With 220V supply (220V - 2.1) / .030A = ~7.3M Ohms
The 7.3 Ohm resister is @ 6.5 Watts
The 230 Ohm resister is @ 207 mW
So what about the LED? What is the different wattage? What if I did 1 million volts? What governs the max voltage?