Why don’t you screw in car lamps? Where do the names halogen and xenon come from? Why do headlights fog up? Today we want to answer these and other questions from carlight blog readers.

There is no such thing as a stupid question. The question why headlights in new cars only come with plastic covers is also a very valid one. There’s no intention here of saving money with “cheap plastic”. The polycarbonate used which is processed in clean rooms is even more expensive than glass. But it won’t splinter in an accident, protecting especially pedestrians, cyclists and motorcyclists from lacerations. This is required by statutory regulations.

Many readers want to know why they can’t simply replace light bulbs with LED versions like they do at home. Well, at home it’s not that important in which direction the light is emitted and how much the output of a lamp is. If in doubt, you can just take a different or more powerful one. Headlights and other lights in cars, however, should always accurately emit their light in the prescribed direction. For example, this requires the light source to sit exactly at the focal point of the reflector, or in other cases the lamp to emit light practically in all directions. This can’t be done with LEDs in the headlight, and is very difficult to do in other lights.

There are other places where readers draw a comparison between car and home, asking why the living room lamp’s practical screw holder doesn’t exist in cars. That has to do with positioning again. For example, the filament needs to sit in an exact horizontal position in the reflector. If screw bases were used, this position would be changed if the lamp is screwed in a bit too tightly or loosely.

You can also get halogen lamps for your living room. But what about xenon for household use? And what do halogen and xenon actually stand for? Both have something to do with gases, and they’re even chemically related. Halogen lamps are filled with a pressurized gas which contains salts. These are called halogens by chemical engineers and ensure that the filament lasts longer and emits more light. In xenon lamps, the gas itself shines, namely in an arc. This is a mixture in which a lot of other gases appear along with xenon. There’s a similar technology used in general illumination. It’s known as a neon tube and is basically the xenon for household use. Overall, engineers speak of gas discharge.

Especially people with a passion for cars and design are extremely bothered about headlights sometimes slightly fogging up inside. How does moisture even get in there? Simple: through the ventilation for the headlights. And why isn’t it encapsulated better? Because the air in headlights warms up and expands; overpressure would then be created in the housing. The whole thing gets reversed when cooling down, and the low pressure would suck in moisture through every little gap. Ventilation ensures that the mist disappears with time, and driving with your lights on has the same effect as warm air defogging the windows inside your car.

Design fans have more questions on their minds. Why on earth do more and more cars have their flasher repeaters, which are prescribed by European rules, in the side mirrors? That doesn’t always look great. Unlike with the plastic covers mentioned at the beginning, the automotive industry’s desire to cut costs does play a part here. Usually a cable harness already leads to the mirror for electrical adjustment and heating. It can also supply the indicator lamp. The flashers used to be installed in the fenders but this required a separate cable.  And besides, flasher repeaters are not common in North America. In any case, because of other rules this region needs different mirrors which then don’t have indicators – so they killed two birds with one stone there.

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