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Yes, HID headlights are legal in South Carolina as long as they comply with specific regulations, such as being within the acceptable color temperature range and not causing excessive glare to other drivers. It is important to ensure that the headlights are properly installed and aligned to meet state requirements for usage on the roads.
If you're smart, you don't. "HID kits" are widely available, but they are (all) illegal and dangerous. See the related link for a detailed explanation.
HID headlights refer to high definition headlights. These are headlights that use LED lightbulbs in them so drivers can see clearer and farther ahead in the dark.
You could find information about hid headlights on Wikipedia, at http://en.wikipedia.org/wiki/Headlamp. Hid headlights are usually attached to the front of a vehicle like a car or motorcycle.
...If they're hid, what difference does it make?
HID headlights are far more brighter than normal Halogen bulbs that are normally in headlights. HID are often thought of as safer because they have a blue glow to them and resemble daylight more than normal bulbs.
Halogen headlamps must use halogen bulbs. "HID kits" are widely available, but they are (all) unsafe and illegal.
If you're smart, you don't. So-called "HID kits" to convert halogen headlamps are widely available, but they are (all) illegal and dangerous; halogen headlamps must use halogen bulbs.
No
Aftermarket HID's are illegal in ANY state. Period.
HID kits are illegal no matter what the "color temperature rating" is. It is illegal and unsafe to install HID bulbs into a headlamp that was not originally designed to accept them.
From what i understand, HID kits are illegal unless you have a projector installed on your car so it controls the light output of the HID's. Projectors spread the light evenly and have a cut off point which don't blind on coming drivers. Don't just install the hid kit, replace your headlights with projects =)