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Lighting Glossary Internal Aim Vs. External Aim Internal Aim: Internal Aim headlamps typically consist of the following components:
Internal Aim headlamps have the reflector and aiming mechanism located inside the headlamp assembly allowing for adjustability without moving the housing. During the aiming process, the reflector moves independently from the housing. The headlamp attaches to the car through the housing. Examples of these are the Chrysler Pacifica and Cadillac CTS External Aim: External Aim headlamps typically consist of the following components:
External Aim headlamps have the whole assembly as one unit. Reflector and lens are typically glued together as one unit. During the aiming process, the entire headlamp moves relative to the car. Examples of these are the current Dodge Ram and the older Dodge Neon. Aiming Considerations The correct aim of a headlamp is very important to the driver as well as for the oncoming traffic. Are the headlamps aimed incorrectly, there is a big risk of causing glare or further distractions to oncoming drivers. . Headlamps that are aimed too high will create excessive glare and look like high beams to oncoming drivers. On the other hand headlamps that are aimed too low will cause reduced seeing performance for the driver Method to corrently aim headlamps The U.S. vertical aiming standard for a VOL headlamp is 0.4º of drop at 25' (this tends to be 2.1”) and the VOR headlamps has no drop. Measure the distance from ground to the headlight centers, and aim the flat part of the beam cutoff at 25' distance (against a vertical wall) to be 2.1" below the headlight center height. Cover one light with something while aiming the other light, and repeat for the 2nd light. Aim the lights straight ahead for the horizontal. This applies to all headlights: projectors and reflector based. However, it is possible to aim projector a few degrees higher due to sharper cutoff.
This picture shows how the headlamp beam pattern is aligned with respect to the horizontal and vertical lines. Please pay attention to which image is VOL and which is VOR.
Reflector Type Headlamps
Relection System Light Source – The light source of a reflector type headlamp can either be a halogen or a xenon bulb. The light source is located to the reflector in a fixed reference / focal position. Reflector (with bulb shield) – The reflector surface is designed to provide the required light output and distribution. Most reflectors are typically manufactured of heat resistant plastic materials. The reflector surface is metalized to achieve the necessary reflectivity. The bulb shield is mounted inside the reflector and prevents unwanted light (glare light) to exit the headlamp. Bezel – The bezel is a cosmetically designed piece of plastic that can be of various colors and shapes. It is used to xenone the hardware designed for moving the reflector during the aiming process. The bezel also covers the gaps between housing and reflector. Outer Lens (with or without optics) – the outer lens builds together with the reflector an optical system. In the case of an optic free outer lens, the entire light pattern is formed by the reflector. If the outer lens contains optics, these optics form, together with the reflector, the entire beam pattern. Housing – The housing is usually made of plastic and is used to hold all the internals of the headlamp assembly, including the lens. The housing is the part that attaches to the vehicle at all times. Projector Type Headlamps The Projection system itself is based on the principle of a slide projector. Below is the diagram of a typical slide projector.
Projection System Ellipsoidal Reflector with condensing lens – The reflector and the lens is what is actually emitting the light coming from the light source. The light is emitted from the light source then reflected off the reflector, and sent through the lens to create the light pattern.
Condensing Lens Shield – The shield inside of a projector is used to create the ‘cut-off’ on the road. Shields make the ‘cut-off’ much more visible than the reflector types.
Cutoff Shield |
