Automotive Headlight Systems and Reflector Technology

Road Lighting Fundamentals

Road lighting systems are designed with specific parameters to ensure optimal visibility and safety. They typically require a minimum illuminated length of 100m and a maximum luminous intensity of 225,000 candela (cd), which represents the luminous flux emitted per unit solid angle in a specific direction.

Beam Distribution Areas (General)

• Discomfort: The first 20m directly in front of the vehicle.
• Width: Between 30m and 50m, providing lateral illumination.
• Comfort: The area between 50m and 150m, offering comfortable long-range visibility.
• Depth: Beyond 150m, for extended forward illumination.

Headlight Projection Systems

Parallel Projection: Parabolic Focus

This system involves positioning the focus of the parabola to achieve a parallel light projection. The height above the ground for this setup is typically between 0.5m and 1.2m.

Convergent Projection: Cross Lighting

In convergent projection systems, often used for cross lighting, the lamp is positioned before the apex of the parabola. These systems utilize convergent projections. To effectively avoid glare, the European code for asymmetric beam patterns is commonly applied. This code ensures greater visibility on the right side of the road, achieved through a specially cut crystal and an inclination of approximately 15° to the right of the screen, positioned below the light beam's filament.

Beam Distribution Areas (Cross Lighting Specific)

• Discomfort: Excessive ground light that hinders forward visibility.
• Width: Between 20m and 30m ahead of the vehicle, crucial for illuminating curves and conditions of poor visibility.
• Comfort: The area between 30m and 60m.
• Depth: Lighting beyond 60m.

Key Automotive Lighting Terminology

Focus:

A point or locus where light and heat rays emitted by a source converge.

Focal Length:

The distance between the focus and the plane of the convex lens, typically between 2cm and 4cm.

Effective Light Intensity:

The intensity of light produced at the output of the optical apparatus.

Reflectors in Automotive Lighting Systems

A reflector's primary purpose is to reflect the light beam produced by the lamps in a specific direction. Reflectors are commonly made from plastic or stamped steel sheet. For steel reflectors, the reflective surface undergoes corrosion treatment before a reflective layer of aluminum or magnesium is applied. Polished aluminum has a reflectivity of 80%, while magnesium oxide reaches up to 95%.

Types of Automotive Reflectors

• Homofocal Reflectors: These parabolic sectors share a common focus, featuring a main reflector and supplementary reflectors attached to enhance front and side lighting.
• Dual-Focus Reflectors: Constructed from two parabolic sections with different focal points. This system leverages the lower reflector to illuminate a specific downward tilt on the road.
• Multifocal (Free-Form) Reflectors: Also known as complex surface reflectors, these are made from different paraboloid sectors with varying focal lengths. They utilize approximately 80% of the lower reflector to illuminate a portion of the road. This system helps eliminate dark areas in the beam, especially at road junctions.
• Ellipsoidal / Poly-Ellipsoidal Reflectors: Designed for smaller light units, these use elliptical reflectors with a projection lens and a screen or diaphragm to define clear light/dark boundaries.

Bi-Xenon Headlight Technology Explained

Bi-Xenon headlights are advanced systems capable of producing both high beam and low beam illumination from a single lamp. An actuator positions the xenon lamp at two different points, thereby achieving different reflector inclinations for high and low beams. The lamp mechanism includes an electromagnetically controlled screen to vary the light-dark boundary, ensuring precise beam control.