text: ?Bi-Xenon? - 996 Series (Carrera, Carrera 4, Carrera 4S, Targa) - RennTech.org Community
  August 15, 2003 in 996 Series (Carrera, Carrera 4, Carrera 4S, Targa)
  I thought I knew this, but, now I'm not sure. I owned the Xenon headlight option on my '99 C4....and I've ordered the P74 Xenon option on my incoming GT3. (sometimes called "Bi-Xenon"?). My buddiie's new GT3 just arrived home with the P74 option and upon inspecting the headlights I find a Xenon low beam in a projector beam housing that levers up and down as the car attitude changes (just like my old '99 Xenons), and a halogen (looks like an H7) bulb below that adds to the Xenon low beam when high beams are selected (just like my old '99). So what's "Bi" about the P74 Bi Xenon option, and how's it any different from my old '99 Xenons? <_<
  From the Tech Information Book
  Additional equipment (I-no.) for all models instead of the previously known "Litronic", is now the new gas discharge light system known as "Bi-Xenon", which, in terms of
  range and road surface illumination, is adapted to the superior performance. In technical terms these headlamps are basically the same as the standard headlamps
  of the 911 Turbo, the only difference being an additional grooving in the protective glass (same as halogen basic headlamps)
  Technically speaking, there is no difference between "Litronic" and "Xenon". Both systems are based on the principle of the gas discharge lamp. Trademark protection of different manufacturers accounts for the different system names. The name "Bi-Xenon" is a reference to the fact that gas discharge lamp technology is also used in the high-beam headlights. Unlike the "Bi-Xenon" system, the "Litronic" system uses a conventional halogen lamp for the highbeam headlight.
  With the Bi-Xenon projection module, the light generated by the D2S xenon lamp is projected onto the road surface by means of a large glass lens measuring 70 mm in diameter. By moving a beam mask, the beam exit area can be enlarged compared to that for the low-beam headlight so that the xenon light (similar to normal daylight) can also be used to produce the spread beam of the high-beam headlight. The mechanical concept of the beam mask is based on an electronically actuated solenoid which moves the beam mask to the high-beam position when the high-beam signal is issued. When the high-beam headlight is switched off, the moving beam mask is raised to the low-beam position and held there by a pretensioned spring so that the specified light/dark boundary is maintained reliably even in the event of a system failure.
  The "Bi-Xenon" system offers the following advantages in low-beam mode:
  * very high light volume
  * more light in the boundary zone in front of the light/dark boundary
  * homogeneous illumination of the entire road surface
  * high colour temperature enables good colour vision
  * the sharply defined light/dark boundary prevents passing vehicles from being dazzled
  * to prevent the driver of the vehicle and the drivers of oncoming vehicles from being dazzled, the headlights are coated with "anti-dazzle" paint at the necessary points and have a periphery illumination reflector
  * Xenon high-beam headlights
  * lowering the beam mask provides a wide and very brightly lit illumination zone even at long range (particularly important on winding roads)
  * supplementary halogen headlights ensure long-range illumination (important when driving at high speeds along straight roads)
  * considerably better switching behaviour when flashing the headlights as well as improved homogeneity compared to previous gas-discharge systems.
  The overall impression of the large headlight with typical Porsche design is achieved thanks to an illumination reflector (to reduce the subjective dazzling of oncoming traffic) and a halogen lamp which is used for the side marker light and which produces light that perfectly matches the colour of the xenon lights.
  Edited August 16, 2003 by Loren
  Thanks Loren...That explains my observations. There is still a supplementary halogen high beam bulb (probably still an H7), but, the Xenon illumination switch to high beam mode is different and improved. So, as before with my Litronics, I may search for slightly better H7 supplementation high beam bulbs.
  The Halogen bulb is for flashing your lights. Xenon systems take to long to power up so the conventional halogen bulb takes its place.