Automatic levelling devices
Manual levelling devices were used in older Halogen headlamps. The way to adjust was directly at the headlamp with a screwdriver. No switch installed on the dashboard.
The adjustment of the low beam has to be carried at every change / repair of headlamps.
The risk of a bad adjustment can include:
- dazzling of oncoming drivers (1% error in the aiming = dazzling is multiplied by 20)
- lack of visibility for the driver (1% error in the aiming = lighting efficiency is 20 times worse at 50 meters)
Further regulation changes have been enacted to control the use of Xenon lamps. Xenon systems generate such a bright light that even dipped lights dazzled in the lower dipped area. For this reason, regulations where brought in that state that an automatic adjustment system must be fitted to ensure that the lights are operating at the correct level regardless of vehicle load. Whereas quartz halogen systems can be fitted with manual (driver controlled) levelling, Xenon systems must have auto-levelling.
This calls for additions like suspension sensors and electric stepper motors in order to identify the need for a change of position as well as to physically make the change. All the above are controlled by a lighting ECU.
The low beam must be aimed in a certain range (between -0.5% and -2.5%) Legislation imposes 6 positions (depending on the load of the vehicle)