This material is principally from discussions
and flame-wars in rec.autos.tech
from 16 December 1989 through January 1990.
Most of this was written with experience from the US. The rules and regulations regarding Automotive Lighting vary some, and sometimes quite widely from country to country (and in the US from state to state). So before purchasing or installing any equipment, check for the regulations which apply in your country or state. You are responsible for the safety and compliance of your vehicle to your local standards.
Basically, in countries where the vehicles travel on the right hand side of the road, the beam pattern is 'level' to the left of the lamp's vertical axis, and rises slightly to the right. This pattern provides for road illumination ahead, and rises to show more of the edge of the road on the right. The vertical adjustment of dipped beams is typically from 0 to 4 degrees below the horizontal, with reference to the 'flat' part of the beam. The dipped beam has a short throw, similar to fogs, though is much narrower horizontally.
High (or Main) beams generally are designed to throw light further than the low beams, and spreading the light up and down from the horizontal axis.
Low beams vary slightly with the design, especially the new Ellipsoidal Reflector designs which have shown up on the BMW's and in the latest big money Japanese vehicles.
The standard style headlamps were originally incandescent tungsten filament sealed beam lamps, not unlike household bulbs. One improvement was to use a quartz-halogen lamp within the same sealed lens unit, this is typical in the USA. Another, superior design, is the European style reflector-lens unit with removable bulb. (These are generally not DOT approved in the USA, except as motorcycle lamps, and are referred to as 'conversion' headlamps.
7" diameter main beams Reflective Range
Dipped Main Beam
Incandescent Lamp 150' 1300'
European H-4 Headlamp (55 watts) 600' 5000'
Be aware that when using quartz-halogen conversion lamps that there is a much greater chance people will think you have high-beams on when you do not. In situations where the on-coming vehicle would normally be within the dimmed lamp, [up/down hills, some curves, nice frost-rippled roads, etc], you may experience more people flashing lamps at you. However, if you get people 'flashing' main beams at you whilst on smooth, straight, or level roads, then check your headlamp alignment, as it may be out of adjustment.
In more recent years the mass manufacturers in the states have again followed the Europeans manufactureres and have introduced 'aero' for flush-fitting headlamps. These are reflector-lens units with a removable bulb, unlike earlier lamps, today these are mostly made of plastic materials. The very latest lamp technology used by mass manufacturers (BMW) is an ellipsoidal reflector and lens design.
Higher wattage bulbs may not be legal in some places. It is possible to have problems with wiring over heating (melting, shorting, which can have a great risk of starting a fire). The only real way to prevent this is to _know_ that all the the power wiring for existing lamps is of sufficient quality to handle the excess current.
More frequently I have heard of the failure of headlamp switches in vehicles which do not use relays between the switch and the lamps. This is more common in older vehicles, but the usually failure mode of an overheated switch is to fail and have no headlamps function. Headlamp switches are usually multi-function switches, and are in a rat's nest of wiring buried in the ignition column. New ones tend to be expensive, and used ones often are hard to locate.
Most of the present day Aerodynamic headlamps are made of composite plastic materials, and it is unusual to find a manufacturer that would recommend or approve of using higher-than-normal strength bulbs in these enclosures.
When replacing headlamp bulbs with higher wattage bulbs, my recommendation would be to find bulbs with 'normal' low (dipped) beam wattage, and stronger main (high) beam wattage. Stronger than normal (45w or 55w) low beams will place a bunch of light in front of you, and in inclement weather, strong light means more dazzle, for oncoming traffic, and also reflected back into your eyes. As for stronger main (high) beam filaments, the longer throw is more useful.
These are examples from various manufacturers, with standard 55 watt quartz-halogen bulbs. Distance will vary between models of the same manufacturer and between manufacturers due to the optical designs of reflectors and lenses, as well as the quality of the materials, etc.~
7" diameter auxiliary lamps Reflective
55 watt Halogen lamps Range
Fog Lamp 1000'
Driving Lamp 7000'
Spot Beam 12500'
In my opinion, for most applications, fog lamps are generally the most useful of the add-on lamps available for users in temperate climates (those that have variable weather).
Fog (rain, snow) does reflect light, thus, any light which rises from the lamp, will be reflected back into the drivers eyes. Thus the designer of a fog lamp wants to aim the light forward and down. Typically a good fog lamp will have a vertical dispersion of about 8-12 degrees down from the horizontal. The horizontal dispersion will be about 110 degrees. This puts light on the road in front of the vehicle, and to the sides, but puts no light up which would be reflected (from fog, snow, rain, etc.) back into the drivers eyes.
The fog lamp housing will incorporate a shield to prevent light from leaving the bulb and then reflecting up. Fog lamps have a relatively short throw, the best being about 250-300 meters (Marchal 900 series, Hella Rallye 2000), typically the throw is less than 200 meters. Fogs are also referred to as 'cornering' lamps in some circles, because of the very wide pattern, allows one to get a good view of where the road is going, with respect to corners and turning opportunities.
Amber lenses, reflectors, or bulb envelopes will diminish the output slightly, while providing better visibility in foggy and snowy conditions. This is due to the effect that the amber colouring tends to reduce 'dazzle' of white beams, and provide for greater contrast in hazy conditions. [The same principle applies to amber or orange coloured 'driving' or 'shooting' eyeglasses. There are a number of tests done, first published by the railway safety organizations which indicated amber and black signs are more visible (day and night) than white and black or other colours.]
About the only time fogs can annoy oncoming traffic is when it would be within your lowbeams, AND when the oncoming lane is lower in elevation than your lane, (even if it is across the median), however the shorter throw reduces the distance and the wide angle means the oncoming driver would be looking nearly sideways to be 'in' the beam.
Fog lights are best mounted closer to the road, and thus the preferred locations are in or below the front bumper (unless you think you'll hit things with them). Some countries limit the distance a fog lamp may be mounted with respect to the road surface, or bumper height. Some countries may require fog lamps to be amber in colour.
It is quite common in some countries to have 'rear' fog lamps, which are basically a normal strength marker or brake light bulb, with a flood-light type red lens.
As fog lamp beams are wide do not rise, they may help to illuminate things to the side and low to the ground. Be courteous to on-coming traffic when the opposing portion of the motorway is below your level. For level opposing traffic, on-coming properly aimed fog lamps should not create any hazard.
Smaller ground-hugging critters may be spotted before the attempt to dart under your wheels. On raised roads, you may see some deer who are (hopefully) contented to graze along the road sides, giving you some warning that the more adventurous ones may be playing in traffic.
In town they help to illuminate low flying objects on the sides of the road - including bouncing balls, short people, etc.
On back roads, the come into use as 'cornering lamps', as their wide beam helps to identify opportunities for left or right turns and how much the road is turning in a curve. They are often used as cornering lamps in competition events (rallyes, etc.).
The initial studies which indicated that yellow/amber and black offered superior visibility or better contrast/definition were years ago by the Railways, which showed black and yellow (or was it yellow and black) as a much more visible combination for signs (than black and white).
US Military specifications for high visibility legends on lit/reflective switches require a green-yellow marking. This is a slight compromise for best day and night visibility. Likewise the 'safety yellow' used for some emergency vehicles in the US, is a similarly a yellow-green.
Similar studies on video display units came up with amber as the preferred tube colour for ease of reading, etc. and the same principles are behind the concepts for amber shooting or amber/orange driving eye glasses.
The loss of brightness is often mentioned as being about 15%, however this varies with the quality & implementation of the coloring.
Driving lamps are probably the second most useful auxiliary lamp for on-road vehicles, especially if you have access to faster roads or drive in open, less-populated areas.
Driving lamps will usually have a beam no broader than main (high) head lamps, but are designed to carry further. Driving lamps should be wired to shut off when the main beams are dipped (low). Driving lamps can be mounted either above or below the bumper, but above is preferred. If you get to drive quite fast and find your main (high) beams insufficient, this is an appropriate lamp, it should not be used in the presence of opposing traffic.
Specialty lamps have various beam patterns which are less useful in normal road conditions, and for the most part are illegal in many places to run on the road. Some of these lamps are for rally and/or off road racing, others are typically found on 'working' vehicles.
For operating principle of QH lamps I'll refer to "Automotive Electrical Handbook", (Jim Horner, HP Books).
As for the operating principles of the Halogen (Quartz-Halogen)
based bulbs, the basic tenants are that
The differences between the H1, H2, and H3 bulbs are basically the mechanical
mounting of the bulb in the fixture and the orientation of the filament with
respect to the base. Each has a different orientation of the filament with
respect to the base, and each base is different (to prevent incorrect usage).
Further references will describe the tip of the glass as the 'top' the metal
base as 'bottom', the top-bottom axis is the 'TB axis'. The reference to the
filament, refers to the coiled portion '_//////_'.
If you are replacing your headlamps with new units, you ought to at least
check the aiming. If you are getting 'flashed' by oncoming traffic when
you actually have your dipped (low) beams on, then you should check the
aim. Many places required that lamps be aimed properly to pass inspection,
and some may be able to issue citations if lamps are very poorly aimed.
For US spec lamps, there are small tabs on the lamp face, and garages
will often have a template or guide which assists them in aiming the
lamp. Most back yard mechanics don't have access to such templates.
This section of the instructions is written for vehicles in countries
which drive on the right-hand side of the road [USA, Europe, etc.]
If you live in the UK, or another country where vehicles drive on
the left hand side of the road, then change right* to left as necessary.
The example mentions a beam which is level and then angles up, this
type of beam pattern is common on European style replacement lamps for
standardized round or rectangular lamps.
The general procedure for aiming headlamps is to find a relatively flat
parking lot, with a wall at one end, that is somewhat dark. You should
have a 'normal' load in your vehicle (have at lest a half tank of fuel,
and don't go and clean out the trunk before hand).
Finding a reasonable parking lot is the hardest part.
Drive up to the wall, mark where the center (horizontal and vertical)
of the L & R lamps are. Best done with coloured tape, 1" or so in width,
make these lines about 6" line, so you'll be able to see them when you
back the car up 20 meters.
Now back the car up 10 meters.
To check the aiming of your headlamps on 'low' or 'dipped' beams, you'll
want to want to have your usual garbage in the trunk and at least a half
tank of fuel. Have the appropriate tool for adjusting your headlamps
handy, as well as a flash light (torch) and something convenient to cover
one of the lights with (a cloth will do, just don't whine at me if you
scratch your own paint with the zipper of your jacket or whatever).
Cover one headlamp and with the dipped beams on,the light patch should
appear as mostly flat across the top, and angled up to the right*.
On a level parking lot, the light from the dipped (low beams) should be
even (or slightly below) the tape marks. The part beam pattern which angles
up to the right* is not counted here, as the raised part, being on the right*
is off the road, not in the view of on-coming traffic.
In general, if the level portion of light is well below the marks, the lamps
are pointed down and need to be raised, the laws in most places allow lamps
to be aimed level (even to the marks) or even slightly down. Unless the
level portion is well below the line, don't aim up at this time. Repeat
this for the other lamp.
If the level portion is above the line, adjust the lamp downward so as
to be level. At this short distance, a noticeable rise means your
''dipped'' beams will rise up into the eyes of oncoming drivers at some
near distance, and they shouldn't.
Most headlamp systems are two set-screws and a fixed point - so adjusting
either set screw may affect aiming along the perpendicular axis. Thus,
while adjust the vertical rise of your lamps, check the horizontal drift.
The horizontal adjustment should be straight ahead, or barely to the
right* for the left* lamp. The right* lamp is often adjusted slightly
further to the right* of center. Neither lamp should ever be to the left*.
The center of the light patch should roughly be at or just to the right*
of where the beam starts to angle up.
After the doing this at 10 meters, move the car back another 10 meters
and repeat the process, at this point you shouldn't need to adjust up,
and maybe just a slight correction down. If you lights change level a lot
as you reverse, then maybe you didn't start with a level parking lot, and
you need to find another log.
Then when you're done at 20 meters, just back up to 30 meters and
double check the fine job you've done.
This allows for a well lit road on dipped beams, without illuminating
oncoming cars. By aiming the right* beam slightly to the right*, it provides
for illumination of the side of the road, helping to illuminate road
signs, etc.
Another trick is to also place hash marks on the rear window to
check for the 'straightness' of the lamps (horizontal aiming), this allows
you to 'target' through the back and front glass where the lamp should aim
on the wall. I've never found this necessary.
Common Bulbs & Mounting differences
Aiming Head Lamps (Main beams)
| |
---+--- ---+---
| |
========================== ground ==================================
LEVEL HIGH LOW If HIGH, then lower
*** If LOW, then raise
| *** **** | *** shows top edge of beam
***** ---+--- ---+-***
| | *****
========================== ground ==================================
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Modification history: HMTL-ified August 1995
Assembled into a FAQ January 1995
Contact: Bill C