Differences in quality of domestic and foreign headlights

The common lamps on the market are basically divided into two camps. Domestic lamps occupy the ultra-low price, while imported lamps have become synonymous with expensive. The quality difference between domestic lamps and imported lamps is mainly reflected in the following three aspects:

1. Accuracy of light pattern

Most of the domestic headlight reflectors are not shaped like computer-aided designs, but are copied directly from molded products. Few manufacturers really study the details. For headlights, the final light pattern depends not only on the design of the reflector bowl, but also on the lens (the transparent glass or polyester cover at the front of the headlight). It is possible to completely imitate the appearance of the two, but when it comes to the refractive index of the lens and the non-point light source provided by the halogen filament, the accuracy of the light pattern is difficult to be simply copied.

We know that the refractive index affects the direction of light passing through the lens; and the distance between the lens and the reflective bowl also directly affects the accuracy of the direction of the outgoing light. The latter is easy to copy, but the refractive index of the lens depends on the material itself, which is difficult to completely copy without the analysis of precision instruments.

Furthermore, the halogen lamp, which is a common light source nowadays, is not an ideal point light source. As we all know, the filament has a certain length, and it is impossible to use simple high school physics knowledge to deal with the refraction and reflection of this light source. If high school physics knowledge can be used directly, we can buy a spherical glass shell, cut it in half, coat the inner surface with a reflective film, and install the lamp at the center of the ball, and it can be used as a spotlight.

In order to accurately control the final light pattern of non-point light sources, you must rely on professional auxiliary design software. After the software calculates the light path of the filament point by point, it looks at the light emitted from different positions of the filament at the point where the light falls, and then the final light pattern design can be obtained (this is also why many people find that the light pattern diverges after installing HID. The light point of the HID light source cannot completely overlap with the halogen lamp. It is usually a curved broken line, similar to lightning). Even when you use a bulb produced with non-standard specifications, it will cause a deviation between the final emitted light pattern and the designed light pattern. A good lamp will allow you to obtain most of the luminous flux within its designed light pattern, and only a small amount of luminous flux falls outside the design area.

2. High temperature resistance and oxidation resistance of reflective bowl coating

The most intuitive way to feel the quality of the coating of the reflector bowl is the reflectivity. Usually, the newly purchased headlights can achieve a good reflection effect. Only on the surface of the reflector bowl of some headlights with extremely poor coating quality can we find a lot of bubbles, impurities, protrusions and other intuitive quality problems. Normal quality products will never let you see these, because this situation is considered a defective product in the general quality control system. However, what really allows us to distinguish high-quality products from aftermarket products is the intrinsic quality of the reflective film.

In order to save production costs and improve reflection efficiency, modern coating technology usually uses aluminum film. However, aluminum itself is easily oxidized due to long-term exposure to the air, forming a non-reflective aluminum oxide layer. At the same time, in order to make the coating fit firmly with the metal base of the reflective bowl, polymer materials are usually used as the basis. When polymer materials are exposed to ultraviolet light, they will age rapidly, resulting in the whitening of the reflective bowl. However, this does not mean that our existing reflective bowls will be aged by sunlight. That little bit of ultraviolet light is just a drizzle for polymer materials. The source of ultraviolet radiation that really causes them to age rapidly is precisely the light source that we let the lamps provide lighting - the light bulb. The light source we are using now is not a single wavelength, its wavelength is continuous, but we cannot see the light in the infrared and ultraviolet regions with our naked eyes. Therefore, many light sources produced by large manufacturers are specially marked: UVcut.

Another intrinsic quality of the coating is its high temperature resistance (of course, this is also related to the heat dissipation design of the lamp itself). The halogen lamps we use are thermoluminescent, and the normal operating temperature of the filament is 2000 degrees Celsius. In the confined space of the lamp, such a heat source can heat the air in the lamp to more than 150 degrees, and the infrared part of the continuous light wave also needs to be reflected by the coating (the reflectivity cannot reach 100%). The three heat transfer modes of heat conduction, convection, and radiation are all heating the coating. Long-term continuous heating will reveal the true colors of the fakes. Among the domestic fog lamp products I have used, none of them can keep their coating on the base of their reflective bowl after 10 hours of night driving, and they are firmly attached. Those that only have small areas of bubbling are considered to be high-quality products.

3. Impact resistance, light transmittance and resistance to sudden temperature changes of the lens

The lens is the transparent cover in front of the lamp, which is usually made of two types of materials: glass and polyester. The biggest advantage of polyester products is its impact resistance. The gravel on the gravel road was rolled up by the tires of the car in front of it and the glass lampshade and windshield were broken. This is probably a heartbreaking experience for many car lovers. When polyester products encounter this situation, usually only a small white spot is left, or a few very fine cracks appear, which will not affect the use of the entire headlight.

In addition, the ability of polyester to withstand sudden temperature changes is also unmatched by glass. After all, the brittleness of glass is much higher than that of polyester. When we turn on the lights and walk through a rainy and foggy road, if the glass quality is not up to standard, simply wiping the lamp surface with a wet tissue will bring endless troubles to your subsequent journey, because the lamp surface will burst into several pieces. In terms of light transmittance, glass is better than polyester in terms of long-term stability. If the quality of polyester is not up to standard, it will age in a very short period of time (six months to one year). At this time, the lens color turns yellow and is accompanied by whitening, while glass is not affected by external conditions such as ultraviolet rays and continues to maintain its initial transparency. In addition, students who pay attention to the light type of the light should note that glass and polyester lenses cannot be directly replaced if they are the same size, because even if the patterns of the two are exactly the same, the difference in the refractive index of the two materials will also cause changes in the light type.