In the US the Porsche HID (known as Litronics) uses the Philips 4100K HID bulbs. I import them as well. They cannot be used alone. HID bulbs run on 35W and require a ballast to power. They do not have filaments like halogen bulbs and they work by igniting an arc in a compressed gas capsule and by exciting the gas creating illumination at 3,200lm. They are about 350% brighter than a 55W H7 halogen bulb.
Because they do not have filaments you need very high voltage to ignite an arc through an air gap. Air is an insulator and it requires 23,000 volts to allow the arc to jump the gap. Here's a simple electrical formula. Voltage X Amperage = Wattage.
A 55W halogen bulb running at 12V will draw 4.58 amps. That is what creates heat. An 80W H7 running on the same 12V will be brighter but now draw 6.66 amps and produce about 46% more heat than the 55W bulb.
A 35W ballast in HID will draw 35W at 12V which is only 2.91 amps and therefore less heat and power from the vehicle. It will simply act as a transformer and raise the voltage to 23,000 Volts and as a result drop the current to around 0.001527 amps (or 1.5 milliamps) That is why HID burns much much cooler than halogen.
Remember, it is not high current (amperage) that's required to ignite the HID bulbs, it is merely high voltage and voltage does not create heat, only current does!
The second item built into the ballast (Hella is used in Porsche and sometimes Bosch, all German made) is the igniter or starter. They help initially ignite the bulb and the xenon gas in the capsule also aids in this process. The more xenon gas, the bluer the light, the more krypton gas, the more purple the light. Philips Ultinon bulbs are rated at 6000K which makes them more purple. The 4100K factory bulbs are pure white. They may give off color at certain angles because they are running through a Hella crystal projector.
The spherical shape of the projector tends to bend the white light at angles and when light is bent the different colors travel at different speed thus allowing faster colors like blue and purple hit your eyes first. The same effect can be seen in a quality cut diamond when it bends the light and gives off colors in the blue-purple hue.
There is alot more technical data about lighting and HID, but this is good general knowledge for those interested. I will link you here to my company's FAQ on HID's for a little more detail.
HID FAQ
Hope this helps shed some light (pun intended!)