Why headlights can become suddenly misaligned

Headlights becoming misaligned all by themselves shouldn’t really happen. Once they’ve been aligned, they should stay that way until the owner or repair shop decides to intervene. But, like many other things that “shouldn’t really” happen, it does occur from time to time. The most important causes are as follows:

1. Something has broken. The internal components of headlights are attached to their housings (and the car body) solely by means of delicate joints and the adjustment screws. Because these parts are mostly made of plastic these days, they can become brittle over time and develop a tendency to break under even a small amount of pressure, such as vibrations while driving. “Fluttering” headlights are a clear sign something has broken.
2. A damaged lens. This type of problem occurs particularly in older headlights that still contain diffusion discs made of grooved glass. With this older technology, the diffusion disc itself plays an important role in light distribution. Where newer, clear lenses are fitted, and in lens headlamps, light is distributed in a different way. Diffusion discs that are cracked or have multiple scratches caused by gravel impact are impaired in terms of how they distribute their beams, and the critical cut-off line that prevents these dazzling other drivers becomes less sharp. Unfortunately, this also happens when the newer, clear plastic lenses become opaque.
3. Headlight leveling is impaired. Headlight beams are only supposed to move up and down when the driver explicitly operates a manual dial or wheel on the dashboard. With automated systems, such as those in xenon lamps, headlight beams move down when extra weight is added to a vehicle. Unfortunately, there are also times when headlight leveling systems take on a life of their own. Bad contacts, for example, can cause the motor to move beams constantly up and down. Or a headlight beam always levels down to the lowest position and stays there. Sometimes a manual adjustment or a different setting will help, but these are not permanent solutions and mean a compromise in lighting quality. As with the other cases I’ve mentioned, a trip to the workshop is recommended.
4. An accidental lower setting. From time to time, drivers change their manual headlight leveling systems accidentally because they confuse the adjustment dial with the brightness control for the instrument panel lighting. It can also be inadvertently changed when cleaning the dashboard. Whatever the reason, such an accidental adjustment can dramatically shorten the range of low beam headlights.

Worn-out bulbs. Filaments expand over the course of their lives. When this happens, they are no longer positioned in the same ideal focal point for light distribution as they were during the original headlight configuration. For drivers using quality bulbs like those from Osram, this effect is so minimal that it is practically negligible. Dubious no-name products are much more likely to cause problems. Generally speaking, however, replacing older bulbs before they finally burn out will prevent any negative effects of the kind mentioned.

Headlights becoming misaligned all by themselves shouldn’t really happen. Once they’ve been aligned, they should stay that way until the owner or repair shop decides to intervene. But, like many other things that “shouldn’t really” happen, it does occur from time to time. The most important causes are as follows:

1. Something has broken. The internal components of headlights are attached to their housings (and the car body) solely by means of delicate joints and the adjustment screws. Because these parts are mostly made of plastic these days, they can become brittle over time and develop a tendency to break under even a small amount of pressure, such as vibrations while driving. “Fluttering” headlights are a clear sign something has broken.
2. A damaged lens. This type of problem occurs particularly in older headlights that still contain diffusion discs made of grooved glass. With this older technology, the diffusion disc itself plays an important role in light distribution. Where newer, clear lenses are fitted, and in lens headlamps, light is distributed in a different way. Diffusion discs that are cracked or have multiple scratches caused by gravel impact are impaired in terms of how they distribute their beams, and the critical cut-off line that prevents these dazzling other drivers becomes less sharp. Unfortunately, this also happens when the newer, clear plastic lenses become opaque.
3. Headlight leveling is impaired. Headlight beams are only supposed to move up and down when the driver explicitly operates a manual dial or wheel on the dashboard. With automated systems, such as those in xenon lamps, headlight beams move down when extra weight is added to a vehicle. Unfortunately, there are also times when headlight leveling systems take on a life of their own. Bad contacts, for example, can cause the motor to move beams constantly up and down. Or a headlight beam always levels down to the lowest position and stays there. Sometimes a manual adjustment or a different setting will help, but these are not permanent solutions and mean a compromise in lighting quality. As with the other cases I’ve mentioned, a trip to the workshop is recommended.
4. An accidental lower setting. From time to time, drivers change their manual headlight leveling systems accidentally because they confuse the adjustment dial with the brightness control for the instrument panel lighting. It can also be inadvertently changed when cleaning the dashboard. Whatever the reason, such an accidental adjustment can dramatically shorten the range of low beam headlights.

Worn-out bulbs. Filaments expand over the course of their lives. When this happens, they are no longer positioned in the same ideal focal point for light distribution as they were during the original headlight configuration. For drivers using quality bulbs like those from Osram, this effect is so minimal that it is practically negligible. Dubious no-name products are much more likely to cause problems. Generally speaking, however, replacing older bulbs before they finally burn out will prevent any negative effects of the kind mentioned.