HID's don't have a filament like a regular light bulb does. They use an arc of high voltage electricity that jumps between two electrodes. That's what the light actually is, an arc of electricity. Also, they are a delicate bulb made from thin glass w/an exposed conductor that runs the length on one side of it. Easy damaged by being heavy-handed.
Think of them as you would a florescent light. The primary power supply is the 115-120VAC provided by the power company, but the lights require a much higher voltage to light and continue operating. The ballast is a step-up transformer that pushes the voltage from 115v up to +/-20,000!! But HID's also require a starter, usually called the igniter that gets things started. In mine they are in-line between the ballast and bulb.
DO NOT put HID's in your high beams. In all places I know of it's illegal to do so, as these are std "reflector," not projector housings. Besides, you will not be doing yourself or other driver's/pedestrians any favors.
HID's do not work like regular tungsten or halogen bulbs and require something to focus their light output, such as the projector lens we already have in our low beams. These are not a perfect solution because they are designed for halogen bulbs, but they work quite well just the same. W/O a projector lens, the light will not be focused and will scatter wildly. You will actually see LESS, but other driver's will be blinded.
This is less critical in fog lights because they throw a low, wide pattern focused by the small housing and fluted reflector (or lens) compared to normal headlamps.
Lastly, take it from me and take the time to remove the front bumper cover and headlamp housings to install HID's.