Jaguar XJ-S. Manual - part 165

 
 

655

 

NOT-SO-BLUE BULBS:  The second type of “blue bulb” doesn’t have the dichroic filter coating that gives the golden 
appearance, but rather a simple light blue tint on the glass.  The objective is white light, not blue.  These are a better 
idea than the golden bulbs described above.  Stern again:  “They come in 9004, HB2 (H4), 9005, 9006, 9007, all DOT-
approved.” 

They’re still not a good idea, though.  Stern goes on to say, “The question of whether these filtered lights might be 
better has been tested by good researchers, and they find not only that any theoretical advantages vanish when the 
context of the study is actual driving tasks on actual roads -- that is, no seeing benefit -- but also there is a glare 
disbenefit with such filtration.  Just say NO to blue-filtered lights of any kind.” 

It is this author’s opinion that the popularity of blue-tinted lights -- other than with morons who care more about being 
“cool” than about safety -- is largely a result of the poor wiring in most automobiles, which causes headlights to operate 
at reduced voltage and therefore appear yellow and weak.  Before considering any blue crap, please install relays or 
upgrade the wiring as discussed beginning on page 642. 

 

YELLOW BULBS:  Yellow is a legal color for headlights, with some areas permitting a yellowish shade of white 
while others permit downright yellow.  This is for good reason; Daniel Stern says, “Until the mid 1990s, headlamps in 
France were required to produce yellow light.  This was accomplished in one of several ways:  yellow headlamp lens, 
yellow glass balloon in front of the bulb, yellow glass balloon as part of H4 bulbs, and dichroic filter coatings on 
halogen bulbs.  This last method was the best, since it produced the required yellow color with very little loss in 
absolute light intensity.  Yellow glass filters caused up to a 15 percent reduction in absolute intensity.  In the mid '90s 
(1994, if I recall correctly) the yellow-light requirement was dropped for new cars in order to bring France into line 
with general European Community regulations.  Yellow bulbs can still be had and used on pre-'94 cars, however. 

“It's not directly apparent that yellow is a magically great color for lights.  It's what happens when you subtract blue 
from an auto lamp.  Blue is the shortest wavelength and, as such, scatters the most readily.  When blue light strikes 
water (rain, fog, snow) it scatters in all directions and makes on-road vision very difficult.  Blue also is a very difficult 
color of light to look at if it is at all intense...it stimulates the reaction we call "glare". 

“So the French figured to remove the blue from the output spectrum of their vehicles' front lamps.  The opposite of blue 
being yellow, the result was French yellow headlamps.  There haven't been any recent comparitive studies, but yellow 
lamps always subjectively ranked as decidedly better in poor weather and lower in glare than white ones, and this 
matches my own experimental experience with fog lamps and headlamps that produce yellow light.  

“One problem with this conclusion as applied to headlamps in France is that the dichroic technology came along very 
shortly before France rescinded the yellow-light requirement.  Therefore, the lamps that were being compared with 
white lamps were almost universally yellow by dint of earlier methods (yellow glass) which reduced the absolute 
intensity of the beam, which may or may not have had a large part in reducing the glare.  Because the requirement for 
yellow light no longer exists (though such light is optional in many countries) we probably will never know the 
vagaries of the answer to this question.  Suffice it to say that yellow light makes a better fog lamp if you intend to use 
the fog lamp in poor-visibility conditions without any drawback in dry conditions, and modern dichroic techniques of 
"yellowing" the light take away some of the drawbacks (reduced amount of light) that used to be a problem with yellow 
lights. 

“These days there are quite a number of dichroic (yellow-pass) lighting products on the market.  There are bulbs with 
this coating, as well as auxiliary lamps whose lenses are so treated.  There's nothing the matter with doing it either way 
(though my preference is for the coating to be on the bulb, because this makes it easy to switch between clear/white 
light and yellow light as desired). 

“There are two commonly available levels of dichroic-filter coating strength on auto headlamp bulbs:  A light coating 
which "skims" the highest-frequency blues off of the output spectrum, causing a yellow-tinted white light, and a heavier 
coating that blocks all of the blue frequencies from being output, causing the full-depth yellow light that we used to see 
in French headlamps.  The deeper yellow tint is more effective at cutting through obscured environments (rain, fog, 
snow, dust), but the lighter coated bulbs meet international definitions of "white" light for headlamps.  I've done 

 
 

656

considerable experimentation with various mixes of bulbs and my own preference for maximum visibility in bad 
weather is: 

-Lightly-filtered headlamp bulbs to produce legally-white light that gives considerably less glareback in bad 
weather 

-heavily-filtered fog lamp bulbs to produce yellow light that does not glare back at all in bad weather (full-
strength yellow is legal in auxiliary lights) 

“I like clear bulbs in driving lamps, because if you're worried about glareback, you're not using your driving lamps!” 

So if the bulbs with blue dichroic coatings appear gold when you look at the bulb itself, what do the bulbs with yellow 
dicroic coatings look like?  “The legal-yellow ones reflect a light purple, while the full-tint ("French") yellow ones 
reflect a deep blue.” 

 

HIR:  Howard Chu mentions another advance in headlights:  “GE's HIR bulbs, which have a bulb coating that reflects 
infrared.  This again allows visible light to escape unhindered, but keeps more heat in the bulb.  The point here is that 
the filament glows because it's hot, so if you can keep more heat in the bulb, you can keep the filament glowing brighter 
with less electricity.” 

 

“XENON” HALOGENS:  Nathaniel Musselman found that Hella offers bulbs that look and work just like standard H1 
or H4 bulbs except that they have xenon gas in them.  They claim that the use of xenon gas improves light output and 
eliminates UV radiation that may damage plastic lenses and housings.  Hella describes these bulbs on their web site at: 

 

 

http://www.hella.co.nz/xenon.html

 

Note that this site claims repeatedly that these bulbs are a plug-in upgrade, but that’s because the site is in New Zealand 
and the guys setting it up forgot that the World Wide Web is world-wide; if the car is US-spec, they will definitely not 
plug in unless you have already upgraded to E-code headlight assemblies. 

Daniel Stern says, “The gas mix in such a bulb does have a higher percentage of Xenon, but it's not exclusively Xenon. 
 Also, the gas mix in the new type bulbs is under higher pressure.  This allows the filament to run hotter, which 
produces more light.  It's not a knock-your-socks-off improvement, but it is certainly noticeable. 

“The newest types of bulbs all use this new gas mix formulation (which also is under a higher pressure).  For instance, 
the H7 is one of the newest headlamp bulbs.  All H7 bulbs have this newly-tweaked, higher-pressure gas mix, and the 
results have been good, with the H7 achieving a higher luminous flux (amount of available usable light) from a given 
wattage (55w in this case) than was achievable in a bulb of this general type with the old gas mix under the old lower 
pressure.  So after a few years' experience with H7s, the manufacturers have moved to update the older traditional bulb 
types with the new gas mix under the new, higher pressure.” 

 

HIGH INTENSITY DISCHARGE (HID):  Gas-discharge xenon lights, such as the strobe bulb in your timing light or 
camera flash, work by firing an arc through a tube containing xenon gas.  HID headlights work similarly by providing a 
continuous arc to provide a continuous light.  These lights have no filament; the arc travels through the gas itself to 
produce the light.  The same arc provides high and low beam; the arc is physically moved from one position to another 
by application of a magnetic field, so the light doesn’t really turn on and off when switching between high and low 
beams but rather “moves”.  The HID headlight system provides a purplish light and gives more light than halogen 
headlights for one third the wattage. 

Daniel Stern:  “HID headlamps, which have a bluish appearance, are legal.  It's because they're not actually blue, they 
just appear more blue than the halogen lamps surrounding them.  They are higher in blue and blue-green wavelengths, 
but this is specifically noted and approved in CMVSS108 and 108.1 (And, for US readers, in FMVSS108).” 

 
 

657

J.C. Whitney (page 691) offers an HID conversion kit that will fit any headlight that uses H1, H4, or 9004 bulbs -- 
which, when combined with the earlier suggestions to replace the round sealed beams with H4 units, means you can fit 
them into any XJ-S.  Cost is a mere $800 per kit -- and you’ll need two kits if you plan to do four headlights. 

Worth it?  Apparently not.  Stern again:  “There are many unsafe, illegal and noncompliant products on the market, 
mainly consisting of an HID ballast and bulb for "retrofitting" into a halogen headlamp. Often, these products are 
advertised using the name of a reputable lighting company ("Real Philips kit!  Real Osram kit!") to try to give the 
potential buyer the illusion of security.  While some of the components in these kits are sometimes made by the 
companies mentioned, reputable companies like Philips, Osram, Hella, etc. never endorse this kind of "retrofit" usage of 
their products. 

“Halogen headlamps and HID headlamps require very different optics to produce a safe and effective -- not to mention 
legal -- beam pattern. It is not some great feat of upgrade engineering to put an HID capsule where a halogen bulb 
belongs, it is just plain foolishness.  Some types of halogen headlamp bulbs (9004, 9007, H3) use a transverse (side-to-
side) and/or offset (not directly in line with the central axis of the headlamp reflector) filament, the position and 
orientation of which is physically impossible to match with a "retrofit" HID capsule.  Even those halogen headlamps 
that use axial-filament (9005, 9006, H1, H7) bulbs are not safely or legitimately "convertible", regardless of what kinds 
of clever products the junk vendors come up with. 

“The most dangerous part of the attempt to "retrofit" Xenon headlamps is that sometimes you get a deceptive and 
illusory "improvement" in the performance of the headlamp.  The performance of the headlamp is perceived to be 
"better" because of the much higher level of foreground lighting (on the road immediately in front of the car).  
However, examining isoscans of the beam patterns produced by this kind of "conversion" reveals less distance light, 
and often an alarming relative minimum where there's meant to be a relative maximum in light intensity.  When you 
think you can see better than you can, you're not safe. 

“It's tricky to judge headlamp beam performance without a lot of knowledge, a lot of training and a lot of special 
equipment, because subjective perceptions are very misleading.  Having a lot of strong light in the foreground that is on 
the road close to the car and out to the sides is very comforting and reliably produces a strong impression of "good 
headlights".  The problem is that not only is foreground lighting of decidedly secondary importance when travelling 
much above 30 mph, but having a very strong pool of light close to the car causes your pupils to close down, worsening 
your distance vision...all the while giving you this false sense of security.  This is to say nothing of the massive amounts 
of glare to other road users and backdazzle to you, the driver, that results from these "retrofits". 

“In order to work correctly and safely, HID headlamps must be designed from the start as HID headlamps.  The only 
safe and legitimate HID retrofit is one that replaces the entire headlamp -- that is lens, reflector, bulb...the whole 
shemozzle -- with optics designed for HID usage.  It is possible to get clever with available products, such as Hella's 
modular projectors available in HID or halogen, and fabricate your own brackets and bezels.  But just putting an HID 
bulb where a halogen one belongs is bad news all around.” 

 

ALTERNATIVE CONTROL SCHEMES:  Besides upgrading the hardware in the headlight systems, there may be 
benefits to changing the ways in which the headlights can be operated.  It would be possible to add dozens of schemes 
here, each complete with wiring schematics, thereby significantly adding to the poundage of this book.  Rather than 
going that route, I have decided to merely put forth some of the more intriguing ideas that have occurred to me or have 
been sent to me, and leave it to the owner to figure out how to implement them if he so desires.  Basically, any of them 
can be achieved with a switch or two, a couple of relays, and a couple hours of fiddling with the wiring. 

John Napoli suggests rewiring the car so that the low beams remain on when the high beams are on, so all the filaments 
are putting out light.  The early European headlamps with two H1 bulbs did this from the factory, and show how easy 
the rewiring is -- simply adding a jumper between terminals 56 and 56b on the main/dip relay.  However, perhaps it 
should be noted that those early cars had separate bulbs for high and low beams, while later cars have both filaments 
within the same bulb.  Overheating or early bulb failure might be the result.  Hence, try this modification at your own 
risk. 

 
 

658

If you have the 4-headlight system, Daniel Stern suggests you can go nuts with control schemes:  “In a quad-round 
system, there are four holes and six filaments.  Nobody ever said you have to have two matching pairs of lamps, or that 
you can't rewire the setup to create 3 beam distributions rather than just two (or even five if you're adventurous).”  Just 
as an illustration, one of Stern’s alternative setups is to provide three levels of light: standard low and high beams, plus 
a “mid beam” arrangement with the outer headlights on high beam but the inner headlights off.  This setup makes good 
sense if the inner high beams are an H1 assembly with really long-range capability, and it only requires one switch and 
a relay.  Using all four high beams will provide truly excellent visibility while you are alone on the road but the H1’s 
can be turned off to avoid blinding another driver you are following at a distance while still keeping the outer 
headlights on high beam to provide good visibility at closer ranges.  And since you have switched from four headlights 
to two, that guy thinks you have switched to low beam already and doesn’t get mad at you for blinding him. 

 

 

Fog/Driving Lights

 

 

FOG LAMPS -- DEFINED:  In the US, fog lamps are yellow illumination lamps mounted low on the front of the car to 
provide visibility in foggy conditions.  However, in some other countries, fog lamps are markers mounted at the rear of 
the car to enable other drivers to see you in foggy conditions.  Naturally, Jaguar is only moderately helpful in keeping 
these two applications distinct in their manuals and schematics.  In this book, “fog lamps” shall always refer to the 
yellow lights at the front of the car; when talking about the lights at the rear, the term “rear fog lamps” or something of 
the sort will always be used. 

 

FOG LIGHT SHORTS:  Jim McGuinn reports that he had an intermittent short circuit in the fog lights that he found 
was the rear of the bulb socket assembly arcing to the housing.  A bit of electrical tape solved the problem. 

 

FOG LIGHT KIT:  While fog lights were standard equipment on XJ-S’s for many years, Bill Kubida reports that 
somewhere around ’93 they became an option -- and therefore Jaguar started offering an official fog light kit.  “The 
addition of the front fog lights requires the addition of a suitable switch to the array of existing switches.  For reasons 
known but to God and Jaguar, the addition of the single additional switch requires the following: 

a) removal of the switch block to the left of the trip computer which has a button for the rear screen heater and 
another for the rear fog lights.  This switch block is then replaced by a new one having a front fog light switch 
and a rear fog light switch; 

b) removal of the switch block to the lower left of the steering column which has a button for the hazard 
warning lights and a blank-out plate.  This is then replaced by a second switch block having a hazard warning 
light switch and another for the rear screen heater. 

“I am certain that if we put a Cray IV to work on it for a couple of years a more complex system could be figured out, 
but personally, I doubt it.” 

 

AFTERMARKET FOG LIGHTS:  If your car didn’t come with fog lights, or your original fog lights met a curb, you 
don’t really need to contact Jaguar; fog light kits are available everywhere, and any rectangular model can be installed 
under the front bumper and look fine on the XJ-S.  It’s a good idea to check on the availability of replacement lenses, 
since they are prone to damage.  You might also check to see if the lenses are thick and substantial to resist all but the 
most powerful impacts.  And you might check the availability of covers. 

You might also wanna check the quality of the light and the pattern.  As with most things, you get what you pay for.  A 
good fog light will direct the light downward around the front of the car, staying under layers of fog if possible; a cheap 
fog light will leak light upward causing glare.