Post Master General
Join Date: Apr 2012
Location: Bowling Green, VA
I Ride: '09 ZX6R
HID work by arcing through a gas, same as a fluorescent light just a whole lot smaller. Usually the gas is Xenon. They were first developed to provide light for arthroscopic surgery, as you can blast the light down a fiber optic line and have all the light dumped out the end of the fiber. When it became practical to install them on cars, it was natural that they would eventually find their way to bikes.
Because they need to produce that arc, the voltage at the bulb is extremely high. During the time it takes the ballast to create that high voltage, the amount of power consumed by the HID system is many times what it consumes once it's up and running at 'normal' temp. 3-5 times more.
That means a 55W HID can draw as much as 275W for the time it takes to charge the ballast. Starting two at the same time means 550W. Total headlight budget for two 55W halogens is 110W....... that means the alternator has to work harder longer, and that makes heat. Usually kills the stator first, after some period of time. Burns up at the top, where the oil cooling is least effective.
Not to mention the heat load at start up, HID also take some period of time to reach full brightness.
LED do not use as high of a voltage, and consume the same amount of power the entire time they are on. More expensive than HID at this point, as they are just entering the market and HIDs are beginning to lose favor so the prices are falling drastically.
"Basic stuff fellas. Use your head for something other than to break your next fall."