The **rear fog lights** are designed to improve visibility in conditions of **fog, snow, heavy rain, and smoke**. However, their use should be limited to situations of **great necessity**, when visibility conditions are really poor. This is because the rear lights are **red** and can dazzle other drivers if used inappropriately.

In the case of **heavy rain**, it is not mandatory to turn on the rear fog light. Its use is recommended only when visibility is extremely reduced, to avoid causing inconvenience to other drivers. Therefore, in situations of heavy rain, but with sufficient visibility, it is not necessary to use these lights.