Principles of rearview mirrors
2023-10-25
The car rearview mirror utilizes the principle of light reflection. The objects on both sides and behind the car, after being reflected by the rearview mirror, enter the driver's field of view inside the car, making it easy for the driver to observe the external conditions of the vehicle. At the same time, car rearview mirrors are either directly designed with a smooth mirror or with a hyperbolic design. The hyperbolic design of the rearview mirror adds a convex mirror design to the outer part of the smooth mirror, which can provide the driver with a wider and farther field of view.
During the driving process of the vehicle, due to the driver driving inside the vehicle and the obstruction of the vehicle body, only the front and left and right areas of the vehicle can be observed, and the rear and side positions of the vehicle cannot be observed. In order to enhance the driver's field of view and ensure driving safety, the car has been designed and installed with rearview mirrors, including exterior and interior rearview mirrors, providing the driver with a wider range of views and better ensuring driving safety.
So, what principle of light does the driver utilize when observing objects outside the car through the rearview mirror? Some people say it is the reflection of light, while others say it is the refraction of light. Let's look at it from the propagation and definition of light.
Reflection of light: an optical phenomenon. The phenomenon of light changing its direction of propagation at the interface and returning to the original material when it propagates to different substances. Light will reflect when it encounters the surface of water, glass, and many other objects. The phenomenon of light changing its propagation direction at the interface of two substances and returning to the original substance is called reflection of light.
Refraction of light: Refraction of light refers to the phenomenon where the propagation direction of light changes when it slants from one medium to another, resulting in the deflection of light at the interface of different media. The phenomenon of refraction belonging to light. The refraction of light, like the reflection of light, occurs at the junction of two media, except that the reflected light returns to the original medium and the refracted light enters another medium. In the phenomenon of refraction, the optical path is reversible.
When viewed from the rearview mirror of a car, objects outside the vehicle are reflected into the driver's field of view through the rearview mirror. Light comes from the air to the rearview mirror (the interface is the mirror surface), and then returns to the air to enter the driver's field of view. So, car rearview mirrors utilize the principle of light reflection, which does not satisfy the phenomenon of light refraction. Light does not enter from one medium to another, nor does it deviate at the interface of the medium. The driver can see the normal contour of objects outside the vehicle through the rearview mirror.
Even if the design of a hyperbolic mirror adopts a partially convex mirror, it still utilizes the principle of light reflection, but the angle of reflection is larger, allowing the driver to obtain more field of view outside the car, rather than using the principle of light refraction.
In addition, in the industry standards related to vehicle rearview mirrors, item 4 of GB15084-2013 "Performance and Installation Requirements for Indirect Vision Devices of Motor Vehicles" requires that the reflecting surface of the mirror should be a flat or spherical convex surface. The reflecting surface of the exterior mirror can be attached to its aspherical part, as long as the main mirror can meet the requirements for indirect vision. The reflectance value of the reflective surface of the sign measured according to the prescribed method should not be less than 40%. Under extreme weather conditions for a long time, during normal use, the reflective surface of the mirror should be able to meet the specified reflectivity values.
Although we have not found any relevant standard explanation from the regulations that car rearview mirrors utilize the principle of light reflection; However, what we can find is that for the requirements of the reflective surface, the value of reflectivity needs to be met. Reflectivity, on the other hand, only exists in the reflection phenomenon of light, and the refraction phenomenon of light involves the refractive index, which is not specified in industry standards. From this, it can also be confirmed that car rearview mirrors utilize the principle of light reflection rather than refraction.
Through the above explanation of the principle of using light reflection in car rearview mirrors, we have also learned that car rearview mirrors use flat mirrors or hyperbolic mirrors with flat mirrors and convex mirrors. The rearview mirror of a car does not use lenses, so there is no use of convex or concave lenses, only convex and flat mirrors. In fact, lenses are mainly used in the lighting of vehicles to diverge or concentrate the light from the vehicle's headlights, achieving different lighting effects.
In addition, we often see that some car owners add various small mirror surfaces on the rearview mirror, including circular and square ones, which are pasted in appropriate positions on the rearview mirror. The added small mirror is actually a small convex mirror, mainly installed on the rearview mirror with only a flat mirror design, which can increase the driver's field of view, observe more external conditions, and improve driving safety. Have you added a small round mirror?If you have any other questions about the principle and use of car rearview mirrors, please feel free to comment or leave a message.
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