It doesn't take much to switch out a head light bulb, but it takes a lot of science to actually create one. Inside those little replacement bulbs is, among other components, one key element: Halogen.
Halogen bulbs are quite common in today's vehicles. Halogen and other gasses combine to create a constant light output throughout the life of the bulb. It's the Tungsten wire within that creates the need for replacement bulbs. Despite the chemical process initiated by the halogen, the wire burns up and the bulb goes out.
And that's why a variety of replacement bulbs are filled with xenon instead. Xenon High Intensity Discharge (HID) light bulbs replace the halogen with xenon and the wire with a ballast, ultimately generating a whiter light source. It is, quite possibly, the most advanced replacement bulbs you can find. (Read more.)
Tire Rack carries a number of xenon-filled replacement bulbs from brands like Hella and PIAA. Search by vehicle to determine what fits.