The main reasons why the brightness of a car headlight bulb decreases over time are as follows:

  1. Filament evaporation: For traditional incandescent lamps, the working principle is to heat the filament with current to make it glow. As the use time increases, the filament will gradually evaporate and become weaker, resulting in a decrease in luminous efficiency and a corresponding decrease in brightness.

  2. Aging of light sources: Whether it is an incandescent lamp, a halogen lamp, a fluorescent lamp or an LED lamp, all light sources will gradually age during operation. For example, the phosphor of a fluorescent lamp will decrease over time, and the luminous material of an LED lamp will also age due to long-term use. These changes will reduce the brightness of the light source.

  3. Dust accumulation on the lampshade or lamp: The brightness of the bulb is sometimes not reduced because the brightness of the light source itself is reduced, but because the car lampshade or lamp has accumulated dust and dirt, resulting in poor light transmittance. This situation can be improved after cleaning the lamp.

  4. Power supply voltage reduction: For some types of car bulbs, such as halogen lamps or some types of LED lamps, if the power supply voltage is reduced, the brightness will also decrease. This may be caused by power grid fluctuations or increased resistance in the circuit.

  Understanding these causes can help you take appropriate measures, such as replacing bulbs in time, cleaning lamps regularly, or checking circuits to maintain good lighting effects.