Picture a lightbulb, one 6V another 12V. if you’re feeding 1A to each one, the 6V bulb will get 6W (6V×1A) while the 12V bulb will get 12W (12V×1A).

Think of the 12V bulb as 2 identical 6V bulbs in series. Same current, but twice the light.

Just play with the math…