here you will find useful basic information and handy tips relating to vehicle headlamps.
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vehicle headlamps focus the light beams generated by the light source onto the road. on this page, find out about the structure of headlamps, and what lighting technology concepts and legal regulations there are, amongst other things. here you can also find useful practical tips for dealing with plastic cover lenses.
important safety note the following technical information and practical tips have been compiled by hella in order to provide professional support to vehicle workshops in their day-to-day work. the information provided on this website is intended for use by suitably qualified personnel only.
the housing of the headlamp has the following tasks:
- carrier of all headlamp components (cable, reflector, etc.)
- fixing to the vehicle body
- protection against exterior influences (humidity, heat, etc.)
- thermoplastics are used as housing material.
the major functional aim of the reflector is to capture the greatest possible share of the luminous flux radiated by the bulb and to direct this towards the road. there are various different reflector systems available to enable headlamp designers to meet this requirement as effectively as possible.
material selection for reflectors
whereas some years ago most reflectors were made of sheet steel, the demands made on headlamps today, such as production tolerances, design, surface quality, weight etc. lead to the use of mainly plastics (various thermoplastics) for reflectors. these are manufactured with a high accuracy of mold reproducibility.
this allows tiered and multiple-chamber systems in particular to be realised. subsequently, the reflectors are coated to achieve the necessary surface quality. in the case of headlamp systems with a high thermal stress, reflectors may also be manufactured from aluminium or magnesium. in the next step an aluminium reflection layer and then a silicon protective layer are vapor-plated onto the reflector surface.
due to their exactly demarcated beam path and high luminous flux, projection modules are used very often in modern headlamps. thanks to different lens diameters, lighting functions, and installation possibilities these modules can be used for a wide range of individual headlamp concepts.
cover lenses with dispersion optics have the task of deflecting, scattering or focusing the luminous flux collected by the reflector in such a way that the required light distribution, such as the cut-off line, is produced. this previous standard concept has now almost been completely replaced by non-patterned systems.
cover lenses without dispersion optics
so-called “clear cover lenses” have no optical elements. they only serve to protect the light from soiling and weather conditions.
they are used for the following headlamp systems:
- inner lens (de system), for low beam, high beam (bi-xenon) and fog light
- separate cover lens within the headlamp, directly in front of the reflector
- free-form headlamps (ff), completely without additional patterning
material selection for cover lenses
conventional cover lenses are generally made of glass. this must be free of streaks and bubbles. however, due to the requirements mentioned previously, the cover lenses are increasingly made of plastic (polycarbonate, pc).
compared to glass, this has numerous advantages:
- extremely impact-resistant
- very light
- smaller production tolerances are possible
- much more design freedom
- the special surface coating makes the lens scratchproof in compliance with ece and sae regulations
tips for cleaning a headlight lens with plastic cover: practical tips
in order to avoid damage to plastic cover lenses, the following information should be observed:
- never clean plastic cover lenses with a dry cloth (danger of scratches)!
- before adding anything to the water in the lens cleaning system, such as a cleaning agent or antifreeze, always check the instructions in the vehicle handbook.
- cleaning chemicals which are too aggressive or of the wrong type can destroy plastic cover lenses.
- never use impermissible high-wattage bulbs!
- only use bulbs with a uv-filter!
lighting technology concepts: comparison
with today’s headlamps, the light distribution on the road is based on two different technical lighting concepts using reflection and projection technology. while the outstanding features of reflection systems are large-surface reflectors behind a clear or patterned cover lens, projector-type systems have a small light exit with a characteristic lens.
headlamp systems: overview
there are four typical headlamp systems
e.g. audi 100 high and low beam
e.g. vw bora
free-form (ff) headlamps
e.g. skoda roomster
super-de headlamps (combined with ff headlamps)
e.g. skoda superb
the reflective surface has a paraboloid surface. this is the oldest technology used for headlamp light distribution. paraboloid reflectors are hardly used today, though. they appear occasionally in high-beam headlamps and large h4 headlamps.
a: if you look into the reflector from the front, the upper part of the reflector is used for the low beam (figure a).
b: the light source is positioned in such a way that the light radiated upwards onto the reflector surface is then reflected downwards over the optical axis onto the road (figure b).
c: optical elements in the cover lens distribute the light in such a way that the legal requirements are met. this is carried out by two different shapes of optical elements: cylindrical vertical profiles for the distribution of the light in the horizontal direction and prismatic structures on a level with the optical axis which serve to distribute the light in such a way that there is more light in the most important spots in the traffic space (figure c).
d: the cover lens of a paraboloid headlamp for low beam has clear optical elements and provides the typical light distribution (figure d).
e: typical low beam distribution of a paraboloid headlamp as an isolux road diagram (figure e).
a: reflective surface used, seen from the front
b: reflection of the light onto the road, seen from the side
c: light deflection through prisms and light scatter through cylindrical optics in the cover lens (seen from above). useful light approx. 27%. 1 reflector, 2 light source, 3 bulb shield, 4 cover lens
d: typical low beam distribution on the cover lens of a paraboloid headlamp
e: typical low beam distribution of a paraboloid headlamp as an isolux road diagram * lx (unit of illuminance – 1 lx results in just enough light to read a newspaper.)
ff headlamps have reflective surfaces which are freely formed within the space. they can only be calculated and optimised with the aid of computers. in the example shown, the reflector is divided into segments which illuminate different
zones of the road and surroundings.
a: thanks to the special design almost all reflective surfaces can be used for the low beam (figure a).
zones are aligned in such a way that the light from all segments of the reflectors is reflected downwards onto the road surface (figure b).
c: the deflection of the light beams and light scatter is made possible directly by the reflective surfaces. this enables clear, non-patterned cover lenses to be used as well, which give the headlamp a brilliant appearance. the cut-off line and the illumination of the right-hand edge of the road are produced by the horizontally arranged reflector segments (figure c).
d: example of light distribution on the cover lens of an ff headlamp (figure d).
e: the light distribution at road level can be adapted to special requests and requirements (figure e).
almost all modern reflection headlamp systems for low beam are equipped with ff reflective surfaces.
a: reflective surface of an ff headlamp used, divided into segments
b: reflection of the light onto the road, seen from the side
c: deflection and scatter of the light directly by the reflective surface. useful light approx. 45%. 1 reflector, 2 light source, 3 bulb shield, 4 cover lens
d: example of light distribution on the cover lens of an ff headlamp
e: typical low beam distribution of an ff headlamp as an isolux road diagram
* lx (unit of illuminance – 1 lx results in just enough light to read a newspaper.)
super-de (combined with ff)
just like de headlamps, super-de headlamps are projector-type systems and work in the same way. the reflective surfaces have been designed with the aid of ff technology. the headlamp is constructed as follows:
a: the reflector captures as much light as possible from the bulb (figure a).
b: the light captured is aligned in such a way that as much of it as possible is directed over the shield and then onto the lens (figure b).
c: the light is aligned with the reflector in such a way that on the level of the shield the light distribution is produced, which the lens then projects onto the road (figure c).
e: typical low beam distribution of a super-de headlamp on the cover lens (figure d).
Read more: Headlight bulb replacement?
e: typical low beam distribution of a super-de headlamp as an isolux road diagram (figure e).
ff technology makes a much greater scatter width and better illumination of the edges of the road possible. the light can be concentrated very close to the cut-off line, enabling the achievement of a greater visible range and relaxed driving at night. today, almost all new projector-type systems for low beam are equipped with ff reflective surfaces. lenses with a diameter of between 40 mm and 80 mm diameter are used. larger lenses mean greater light output, but also more weight.
a: reflective surface used and shield shape (seen from the front)
b: generation of the cut-off line and slight shuttering by the shield (side view)
c: beam path and light concentration in the focal space (view from above). useful light approx. 52%. 1 reflector, 2 light source, 3 bulb shield, 4 lens, 5 cover lens
d: typical low beam distribution of a super-de headlamp on the cover lens
e: typical low beam distribution of a super-de headlamp as an isolux road diagram
* lx (unit of illuminance – 1 lx results in just enough light to read a newspaper.)
vehicle lighting regulations: good to know
installation instructions seen from the front
due to the scope of the statutory regulations, only the most important are explained here. the following regulations contain all the relevant information about headlamps, their properties, and uses:
76/761/eec and ece r1 and r2
headlamps for high and low beam and their bulbs
headlamps with h1 to h11 (except for h4), hb3 and hb4 lamps
headlamps with h4 bulbs
stvzo § 50 (german road traffic act)
headlamps for high and low beam
76/756/eec and ece r48
for attachment and use
headlamp with gas discharge lamp
headlamp with asymmetric low beam (also led)
advanced frontlighting system (afs)
|headlamps for low beam|
|width position||max. 400 mm from the outermost point|
|height position||500 to 1200 mm permissible|
|electrical circuit||switching on pairs of auxiliary headlamps in addition to the low beam and/or high beam is permitted. when changing to low beam, all high-beam headlamps must switch off simultaneously.|
|switch-on control||green indicator lamp|
|miscellaneous||if the headlamps are fitted with gas discharge lamps (high and low beam), automatic headlamp leveling and a headlamp cleaning system also have to be installed. these requirements also apply when such headlamps are retrofitted to vehicles already on the road if the retrofitting took place after april 1, 2000.|
|headlamps for high beam|
|number||two or four|
|width position||no special regulations but must be installed in such a way that the driver is not disturbed by reflections.|
|height position||no particular specifications|
|electrical circuit||switching on pairs of auxiliary high-beam headlamps in addition to the low beam and/or high beam is permitted. when changing to low beam, all high-beam headlamps must switch off simultaneously.|
|switch-on control||blue indicator lamp|
|miscellaneous||the luminous intensity of all the switchable high-beam headlamps must not exceed 300,000 candela. the sum of the reference numbers may not be greater than 100.|
|headlamps for fog light (optional)|
|number||two, white or light amber|
|width position||no particular specifications|
|height position||not higher than the low beam headlamps, but according to ece at least 250 mm|
|electrical circuit||with low and high beam. also possible with marker light if the light exit area of the fog lamp is no further than 400 mm away from the outermost point of the vehicle width.|
help in deciphering the combinations of numbers and letters on headlamps: the headlamp housing shows all the headlamp versions that are used in one vehicle type.
type approval numbers on the headlamp
national and international design and operating regulations apply for the manufacture and testing of vehicle lighting equipment. special approval marks exist for headlamps and can be found on the cover lens or on the housing.
the following can be found on a cover lens hc/r 25 e1 02 a 44457:
- code hc/r means: h for halogen-, c for low beam and r for high beam.
- the slash between c and r means that low beam and high beam cannot be switched on simultaneously (h4 main headlamps).
- the following reference number provides information about the luminous intensity of the high-beam headlamp.
- the code e1 means that the headlamp has been approved in germany.
- 02 a indicates that there is a marker light (parking light) (a) in the headlamp, the regulations for which have been revised twice (02) since publication.
- at the end is the five-digit type approval numberwhich is assigned individually for every headlamp design approval.
ece regulation 1
- a marker light
- b fog light
- c low beam
- r high beam
- cr high and low beam
- c/r high or low beam
ece regulation 8, 20 (h4 only)
- hc halogen low beam
- hcr halogen high and low beam
- hc/r halogen high or low beam
ece regulation 98
- dc xenon low beam
- dr xenon high beam
- dc/r xenon high or low beam – simultaneous operation is prohibited.
ece regulation 123
- x advanced frontlighting system
marking illuminance reference numbers
7.5; 10; 12.5; 17.5; 20; 25; 27.5; 30; 37.5; 40; 45; 50 per headlamp (in germany max. four simultaneously switched-on high-beam headlamps are permitted, and the reference number 100 or 480 lx is the maximum value that must not be exceeded)
left- and right-hand traffic
headlamp – direction of traffic flow
- left-hand traffic no arrow: right-hand traffic
- left- and right-hand traffic