There are many reasons for poor light. But most of them fall into four categories:
Headlight lamps are optimized for 13.2 volts. That is, the headlight lamps used in passenger cars. Some car drivers have reportedly headed off to a truck stop “to quickly pick up a H7” and then blown a gasket when they saw how bad the light was. In the process, they simply forgot that truck stops are primarily used by truck drivers. And their trucks have 24-volt systems. Joking aside, all it takes to check the operating voltage is a multimeter. Initially on the battery: The level should be at least 13.2 volts, as stated above, while the engine is running. A level of 13.5 volts to 14 volts would be good. Expert amateur mechanics will then check the voltage of the headlights. But be careful! You can easily cause a short in the confined space of the engine compartment, and the headlight wiring occasionally is not equipped with a fuse. Measurements cannot be made on xenon headlights. There are a couple of reasons for this. First, a surge of several ten thousand volts is created when the lights are turned on. Second, the xenon light barely reacts to fluctuations in voltage.
If the onboard voltage is outside the range of 13.2 volts to 14 volt, it’s time to call the auto service center.
The performance of every halogen lamp deteriorates during operation. It can decline by 30 percent at the end of the lamp’s service life. For xenon lamps, it can even be more than 50 percent. But performance can be restored simply by replacing the lamps before they burn out. Such a switch makes perfect sense following the purchase of a used car. After all, buyers know little about the quality of the lamps installed in the vehicle. The differences in quality are huge. Professional lamp tests conducted by the German publication Auto Bild have found that no-name products will produce less than half of the prescribed light. Upgrading to a high-performance lamp like the die Night Breaker Ultimate made by Osram will improve light.
Headlights age, just like the entire car. The reflector can fall victim to wear, too. Rust is no longer a concern today because the part is generally made of mirrored plastic. But a number of adverse conditions can cause damage to the high-gloss surface. One of the most brutal forces is high-pressure cleaning systems. If water, or, in the worst case, the cleaning agent itself, gets into the casing, these systems will leave behind traces of lime – in the best-case scenario. Even those will reduce the optical qualities of the lamps. The lesson: Use the “cleaning lance” carefully! Unfortunately, the reflectors of today’s headlights can rarely be replaced individually. Headlamp lenses have the same problem. An accumulation of scratches can diminish their optical qualities as well.
One of the most frequent causes of poor light – or expressed in a better way: poor visibility – is improper headlight adjustment. It makes sense to do an inspection at the end of any other measure. New lamps will illuminate the road even more precisely if the headlights were readjusted along with them. You will probably not notice a difference for the first few meters in front of the car. But you will see a change at a distance of 50 meters or more on the right side of the road. Readjustment is a really important step to take after disreputable no-name lamps are replaced with brand-name products. The reason: If the old light source was outside the tolerance range, the setting will not work with the new lamps.