Headlights

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.

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.

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

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

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.

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).

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 areas of the road and surroundings.

A: Thanks to the special design almost all reflective surfaces can be used for the low beam (Figure A).

B: Areas 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.

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).

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.

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

ECE R8
Headlamps with H1 to H11 (except for H4), HB3 and HB4 lamps

ECE R20
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

ECE R98/99
Headlamp with gas discharge lamp

ECE R112
Headlamp with asymmetric low beam (also LED)

ECE R119
Cornering light

ECE R123
Advanced Frontlighting System (AFS)