Hector Fratty

Xenon 25W is increasingly being seen and planned as an optimal solution for better lighting in the near future for most cars. Evaluated on its merits, it is probably the best compromise between better lighting performance and cost.

The 25W Xenon system has five advantages and one obstacle. The first two advantages, weight and volume reduction, were presented in last week’s newsletter.
Now we discuss two more advantages; the remaining one and the challenge will be discussed next week.

Advantage 3: shorter Light Centre Length.
Why do HID bulbs look like they have since 1989? It’s because at that time it wasn’t yet certain whether projector or reflector optics would be the preferred solution for Xenon headlamps. The reflectors in use at that time had focal lengths of 24 to 27mm, while the projectors had focal lengths of 13 to 16 mm. The LCL, the distance from the bulb reference plane to the beginning of the light source, was set at 27.1 mm; this is close to the H1 bulb’s value of 25mm. By and by, reflector optics lost the competition.
In Europe, Xenon reflectors play absolutely no role anymore; 100% of new developments are projectors. In America and Japan, the reflector shares are dropping constantly due to the emerging AFS systems, in which projectors offer more flexibility in turning with a simple pivot. Early in the history of Xenon headlamps, an LCL similar to that of the H1 bulb (with which there was a great deal of accumulated experience in reflector and projector optic design) prevented a substantial additional challenge in designing new optics for the new light source.
Now that optical techniques for Xenon are well established and the projector is clearly the preferred solution, there’s strong incentive to seek a shorter bulb. The European expert working group discussing the 25w Xenon system is presently favoring an LCL of 17.1 mm, 30% shorter than present 35w Xenon bulbs. This is a 10 mm savings in geometry and depth. This is a significant step because the dominating and longest element in headlamps is the projector. 20 years ago, packaging constraints were a good bit less tight than they are today, so there was no real impetus to think about these 10mm. Now we have a new opportunity to do so.

Advantage 4: Low-voltage external electrics
HID headlight bulbs are lit with an arc started with high-voltage pulses; steady-state operating voltage is 80v (bulbs with Hg) or 40v (mercury-free bulbs). Past system designs needed costly interfaces with high-voltage connectors, EMI-shielded cables and often very late and expensive activities in EMI/RFI countermeasures. The fully-integrated 25w system presently under development is targeting a solution with fully-contained high-voltage electrics; outside the bulb/ballast module would be only automotive line voltage of 12V or 24V. What does that mean for the car manufacturer, the set makers and the end users?