Biliten Knowledge Sharing: What is a rear fog light? What are its characteristics?

Author: Biliten

2025-05-29

Previously, we introduced the design features of the front fog lights and the precautions when using them. In this article, we will talk about the rear fog lights.

Definition of Rear Fog Lights

Rear fog lights are special lights installed at the rear of a vehicle and are part of the vehicle safety lighting system. They are designed to emit high-intensity light in extremely low-visibility weather conditions such as rain, fog, snow, and dust, so that drivers of vehicles behind can clearly identify the position of the vehicle, thereby reducing the risk of traffic accidents such as rear-end collisions.

Main Functions of Rear Fog Lights

Enhance vehicle visibility and warn vehicles behind: In rainy and foggy weather, you need to not only see the road conditions yourself, but also be seen clearly by others. The strong light penetration ability of rear fog lights far exceeds that of ordinary taillights, which can effectively remind vehicles behind to keep a safe distance and slow down.

Installation Position of Rear Fog Light

1. Height requirement:
The center of rear fog light should be within 0.3~1.5 meters from the ground (GB 4785 standard) to ensure that the light can penetrate the fog near the ground (the fog layer is usually close to the ground).
2. Left and right distribution:
(1) Single rear fog light: mostly located on the left side of the rear of the car (symmetrical with the left taillight) to avoid confusion with the right reversing light (usually white) (such as EU models).
(2) Double rear fog light: symmetrical installation (such as most Chinese models) to enhance signal balance, but pay attention to keep a distance from the brake light to avoid light signal overlap.

Design Features of Rear Fog Lights

1. Light characteristics

Color: must be red (same color as brake lights and tail lights, but brighter).
Brightness: 3~5 times brighter than ordinary tail lights, ensuring that they can still be clearly seen in bad weather.
Beam angle: designed to diffuse light to avoid direct glare to the rear vehicle.

2. Installation location

Single-side installation (common): Most vehicles are equipped with only one rear fog light (usually on the left) to avoid confusion with the brake light.
Double-side installation (a few models): Some high-end models or models in areas with strict regulations will install two rear fog lights

3. Switch and control

Independent switch: Usually located on the light control lever or center console, with a special logo for the rear fog light. (Yellow or orange)
Linkage logic: The low beam or width indicator lights must be turned on first before the rear fog lights can be activated (to prevent accidental activation).
For some models, the rear fog lights will automatically turn off after the headlights are turned off.

Are Rear Fog Lights Brighter, the Better?

Of course not.

1. Rear fog lights use scattered light. Scattered light that is too bright is extremely dazzling. In the dark or with low visibility, it may cause the rear driver to temporarily go blind, increasing the risk of rear-end collision.
2. The color of rear fog lights is similar to that of brake lights. Strong light can easily cover the brake light, causing the rear vehicle to be unable to detect the actual braking of the front vehicle in time, delaying the reaction.
3. Many laws and regulations limit the parameter requirements of rear fog lights. Brightness that exceeds the legal limit can easily cause the vehicle to fail the annual inspection or even be punished.

Why Does My Car Only Have A Rear Fog Light on One Side?

Some careful car owners will find that only the left side of their car has a rear fog light. This design involves the following aspects:

1. Visual distinction function to avoid confusion with brake lights: The rear fog light (red) and the brake light (red) have the same color. If dual rear fog lights are installed on both sides at the same time, it may cause the driver of the rear car to have difficulty in quickly distinguishing between "brake signals" and "warning signals" in rainy and foggy weather, increasing the risk of misjudgment.

2. Regulatory mandatory requirements: Originated in Europe in the 1980s. At that time, the European Economic Commission introduced a single rear fog light standard for vehicles with a total mass of ≤3.5 tons (such as passenger cars), allowing only one rear fog light to be installed on the left side. Large vehicles (such as trucks and buses) still need dual rear fog lights to enhance the warning effect due to their wider bodies. Subsequently, Japan, Australia, New Zealand and other countries continued to adopt this set of EU regulations, and some models adopted a single rear fog light design; although China did not mandate single/double rear fog lights, the early European models (such as Volkswagen and BMW) retained the single rear fog light design, while domestic models mostly adopted double rear fog lights.

3. Balanced design of left red and right white: Early EU regulations (later borrowed by many countries) required a single rear fog light to be located on the left, forming a symmetrical layout of "left red and right white" with the reversing lamp (white) on the right. This design uses the human eye's sensitivity to color and position to help the following vehicles quickly identify the function of the light (red for warning, white for lighting) and reduce confusion.

Precautions for Using Rear Fog Lights

1. Turn on as needed: The rear fog lights can be turned on in rainy, foggy, dusty or visibility less than 100 meters. It is strictly forbidden to turn on the rear fog lights on sunny days or when visibility is good, because the strong light may burn the eyes of the driver of the rear vehicle and cause a rear-end collision.

2. Avoid abuse: Pay attention to the order of turning on - turn on the width lights or low beam lights first, then turn on the separate rear fog light switch; do not turn on the rear fog lights directly or use the hazard warning lights (double flash) instead of the rear fog lights
3. Regular inspection and maintenance: Check the rear fog lights regularly every month to see if they are working properly. Be prepared. If the bulb is damaged or the line contact is poor, it needs to be replaced and repaired in time. Do not be careless.

Summary

Rear fog lights are safety tools in extreme weather conditions, not daily lighting equipment. Reasonable use can not only protect your own safety, but also avoid causing interference to other road users, reflecting civilized driving quality.

What is the most important factor of auto led light?

BILITEN Knowledge Sharing: What is a front fog light and what are its characteristics?