I just a little confused on a couple of things. I know that “Power in is Power out!”
Watts (Power) is the product of Amps (current) x Volts.
In a resistive load like a light bulb, the resistance does not change significantly (well maybe a little with the difference in heat). We can assume that it does not, so this parameter does not even enter into the equation.
Power (watts) = Volts x Amps.
100W = 220V x ?A
Or
?A = 100W/220V.
A = 0.4545
Complete- 100W = 220V x 0.4545A
A 100W light bulb will draw 0.4545 amps of current at 220 volts of electrical potential.
NOW let us change the Voltage.
100W = 120V x ?A
?A = 100W/120V
A = 0.8333
Complete- 100W = 120V x 0.833A
A 100W light bulb will draw 0.833 amps of current at 120 volts of electrical potential.
The Power (Watts) Does not change.
If you change the voltage, and the Resistance of the load does not change, the Amp draw is what is changing. NOT THE WATTS.
It will still be a 100W light bulb.