Xenon lights vs. projector beams (longish)

["Frank Amoroso" <famoroso@sprintmail.com>]

Judging by the responses I have gotten, it seems as if not everyone is aware
of the differences between a Xenon headlight and a projector beam headlight.
So sorry for the BW here but I am pretty Philesque when it comes to lighting
technology. I take freely from personal research, Hella, PIAA, and Osram
literature, etc.

Let's start with a regular headlight which has been in use forever. A
parabolic headlamp has a paraboloid reflector. The bulb filament is located
at the focal point. The reflector picks up light from the bulb and reflects
it as a parallel beam. The beam is distributed by the lens which is
optically patterned (very poorly in the USA). The headlamp sometimes has a
bulb shield to stop drivers of oncoming vehicles from being blinded. This
means that part of the light from the bulb is lost. An effective paraboloid
headlamp needs a relatively large reflector, to collect allot of light, and
its lens is as vertical as possible. A reflector with a large focal length
is good for long range light. Conversely, one with a short focal length is
good for short range light. Examples: pretty much any car manufactured prior
to 1985 has this type of headlamp, the current Jeep Cherokee and Wrangler
still do.

Next let's discuss projector beam headlamps. These look like an "eye" and
are more expensive to produce than a parabolic headlamp. A projector beam
headlamp functions  rather like a slide projector. The bulb is positioned at
the focal point on the ellipsoid (the reflector). A shield (instead of a
slide in our projector example) is used to produce the light cut off (at an
angle in th e case of Euro low beams, or flat in the case of fog lights).
The convex lens projects the light (very accurately) onto the road. Thanks
to this design the lens can be raked more sharply. The end result is more
light output for better vision, a sharper cut off, and minimum glare.
Projector beams are smaller, and more expensive, but produce superior
lighting performance. Sometimes the lens has a certain color and the ensuing
light that is thrown could be mistaken for the bluish light that Xenon
lights emit.

Xenon or High Intensity gas Discharge (HID) lighting systems emit daylight
quality light and brightness far outshining and outdistancing most high
beams. Without the use of a filament HID lamps fire an electric charge (in
the case of Hella, 28,000 volts) to strike the arc in a pressurized capsule
of Xenon. At this point the system in the 911 Turbo runs the lights on 35
volts AC. The results are pretty impressive, consuming one third the energy
of standard halogen lighting while delivering three times the beam power.
This technology significantly reduces heat generation. Which brings us to
color temperature or Kelvin rating. Color temperature is a unit of measure
for the color of light , it is not related to the heat of the light source.
A higher color temperature represents a color closer to actual sun light.
>From the red end of the spectrum to the blue: 2600K Incandescent Bulb, 3200K
Halogen Bulb, 4300K HID Bulb (PIAA), 5250K Sun Light.

Here is the part that has been confusing some listers: Xenon's are (to the
best of my knowledge) always projector beams, but projector beams are not
always Xenon's. This is due to the superior light dispersion of the
projector beam focal system. So, to recap, projector beams are a way of
aiming the light on the road and a Xenon set up describes the light source.

Gas discharge lamps have been in use for many years where high-intensity
light and high efficiency have been needed, notably in international sports
stadiums. In close cooperation with European lamp, headlight and car
manufacturers, OSRAM has managed to apply this technology to cars. Of
course, the dimensions of the lamps had to be considerably reduced.
As explained, gas discharge in an automotive lamp is like a miniature flash
of lightning. A high-voltage pulse is applied to two contacts in a glass
bulb filled with xenon, one of the inert gases. This voltage is discharged
in a spark-over between the contacts to produce a very bright arc only a few
millimeters in length. Once this arc has been produced, voltage can be
considerably reduced with the aid of electronic control gear, so that the
xenon lamp consumes only half as much electricity as a conventional halogen
headlight lamp, despite giving out more than twice as much light.
In 1991, the first BMW with the new OSRAM xenon lamps for the dipped beam
rolled off the assembly line. A large-scale field trial produced extremely
encouraging results. Practically all drivers polled (89%) felt safer with
xenon headlights at night-time and in poor weather conditions. The light was
found to be more comfortable and less of a strain on the eyes. Drivers were
able to read road signs and spot objects on the road at greater distances
than they could with conventional headlight lamps.
The new light sources also offered benefits to the automobile industry.
Since xenon lamps emit much less heat than tungsten-halogen lamps, designers
were able to create more compact, and more aerodynamic headlights. The gas
discharge lamp therefore offers three major advantages all at once: new
design options, improved aerodynamics which leads to a reduction in fuel
consumption, and lower power consumption to the benefit of other parts of
the car's electrical system.
In the Autumn of 1994 the second-generation xenon headlights were
introduced. Since then, all cars with xenon light are also fitted with an
automatic headlamp beam adjustment system. Last I checked, thanks to the
DOT, this height adjustability was illegal in the USA, while it has been
standard issue in Europe. This adjusts the position of the headlights and
hence the direction of the light beam to compensate for heavy loads and
bumpy roads.

Hopefully this clears up some of the recent confusion regarding different
lighting systems. If you have a halogen bulb be it 9004, 9006, H4, H1, etc.
you do not have Xenon's. If you need to purchase a Xenon capsule you are A)
styling, and B) hating it, because the life of a Xenon capsule should far
exceed the life of the vehicle.

Exclaimer: I do not work for or have any affiliation with Hella, PIAA, or
Osram, but I wish I did!

                                    Hope this helps,
                                    Frank "Desperately Seeking Xenon"
Amoroso
                                    '93 S4