The new auxiliary lights for commercial vehicles from Hella are subjected to extensive testing – simulation under road conditions in Europe's largest light tunnel
Before a new auxiliary headlamp for trucks from Hella "sees the light of day", it is subjected to a marathon of inspections and tests. For example, the influences of heat, cold, moisture, splashes and permanent stresses are thoroughly examined. After all, commercial vehicle headlights are especially required to function perfectly in a range of climatic and road conditions. "We work under time pressure in the most difficult conditions. We have to be able to rely on our light - everywhere and at all times", says Detlef Tillmann, General Manager of Kreuzburg GmbH in Hagen, Germany.
Hella therefore subjects the new commercial vehicle auxiliary lights to extensive construction, testing and inspection programmes. The selection of materials is also extremely important. For permanent use in changing conditions, usually only a housing made of metal and premium plastic comes into question. A special weatherproof seal also offers reliable protection for use in changeable climate zones. The light holders are made of metal in order to safely and consistently withstand vibrations, shocks and rolling motions. In addition, during construction on the CAD monitor using Hella's own programme, not only is the best light power calculated and simulated, but the most favourable type of reflector with the least build up of heat is established. Highly concentrated heat radiation should be avoided because high heat stresses have a direct effect on the durability of the materials.
A hard series of tests then begins for the prototypes: a solar simulator with 1600 Watts of power radiates bundled light onto critical zones on the headlight and tests whether the burning glass effects do not thermally overexert the composite materials. The resistance to temperature changes is then tested in the climatic chamber. The prototype is constantly changed from one extreme to the other – the climatic chambers are subjected to temperatures between minus 70 and plus 180 degrees Celsius, whereby changing humidity levels are also possible. If required, these climate changes can be carried out over a period of weeks. A quick succession of temperature shocks is produced in a double chamber system in which a lift transports the light back and forth between the temperature extremes within a few seconds. These tests ensure that the plastic used does not become too brittle in low temperatures or too flexible in high temperatures.
These tests are followed by ongoing tests on vibrating machines which apply different oscillations in frequency (how frequently per second) and amplitude (how large in the hub) to the prototypes. This helps recreate driving operations on poorly maintained roads and ensures that the heavy glass lenses, for example, can be permanently attached to light plastics, despite their heavier mass, and can withstand the dynamic occurrence of changing vibration stresses at all times. In the 24 hour operation test, the light remains switched on for 24 consecutive hours. This is how it is ensured that the surface desposition of the reflector does not detach or change, by becoming matt for example. Such a change would not only be visible on the clear glass, but would also have a negative effect on the quantity of light available on the road.
In the heat test, the light is subject to a temperature of 50 degrees Celsius for an hour in order to simulate a traffic jam in summer. No deformations should occur here. The reflector must also withstand the respective temperature increase in the housing without any damages. In the splash test, the light is constantly sprayed from all sides in a closed chamber with a swivel bar with 24 high-pressure water nozzles. If the lights manage this, rain, splashes or cleaning in a vehicle wash should be no problem at all. In the condensation test, the light is constantly switched on and off while subjected to high moisture levels – by sprinkling with cold water for 24 hours. Due to the switch process, the light "breathes" throughout the whole testing process in an environment with almost 100 percent humidity. Condensation builds up in the light: that is completely normal, but after a certain amount of time, the condensation should have disappeared again thanks to the integrated ventilation.
In the largest light tunnel in Europe, near to Hella in Lippstadt, the illumination power of lights is tested under road conditions. Test lights can be attached at six levels on 2.50 metre wide rollers. This allows the height of the light in the actual vehicle to be considered. A lifting platform behind the rollers positions the tester at the seat height of the truck driver. The test specimens shed their light on a 140 metre long dark road fully enclosed with black walls. Guide posts at distances of 20 metres provide orientation for the test of the illumination quality, length and width. Possible glare for oncoming traffic or the identification of sources of danger is always tested – animals crossing the road are simulated with grey shadows and pedestrians are made of cardboard figures; they cross the road from the sides. Fog can also be effectively simulated.
In addition to going through extreme quality tests, the Hella auxiliary lights are characterised by the fact that they are homologised according to the type requirements of the EU authorisation process (ECE type test). Constantly good quality in series production is also important. Due to the fact that Hella works at the high quality standards of the automobile industry, where the specifications are usually higher than the international norms, high quality and high performance of the lights is always guaranteed through the quality of the tools, the production systems and the quality assurance processes.