OK, here we go.....
Normal bulbs are incandescent, which means they have a filament (little wire coil). Most car bulbs are sealed bulbs with halogen gas to help stop the glass from shattering from the heat generated.
Lately they have been using Xenon gas to allow the filament to run hotter and whiter, to aproduce more light from the same wattage filament.
REAL Xenon bulbs, such as the 172 et al. have HID bulbs, which stands for High Intensity Discharge. Some older cars (E36 BMW, some Mazdas) use these bulbs, but they are not the Xenon type, maybe halogen.
HID bulbs have NO filament. They are a high pressure bulb, the size of a golf ball, which is filled with gas, say Xenon. There are two electrodes on the back of the globe, which pass high amounts of current, which excites the gas, and the gas ionises, and emits photons of light (yay chemistry lesson!).
So, you CANT put normal filament type Xenon replacement bulbs into a old car and expect the same brightness and colour as a 172, which has HID bulbs.
Thats why the Cup has no xenon. the whole unit must be heavier (even though i think they should throw away the bumper bars b4 they throw away those beautiful xenon headlights
)
So, there you have it. in a nutshell...
hope this helps...
Paul
