To drive safely in conditions of **very heavy rain**, it is important to use the **rear fog light**. This light helps other drivers see your vehicle more clearly when visibility is reduced due to heavy rain. Although the provided fragments do not specifically mention the rear fog light, it is important to know that its use is crucial in low visibility conditions, such as heavy rain, to prevent accidents.

On the other hand, in situations of **strong wind** or **heavy traffic**, it is not necessary to turn on the rear fog light, as these conditions do not affect visibility in the same way as heavy rain. Therefore, the rear fog light should be used specifically to improve visibility in adverse weather conditions that reduce visibility, such as heavy rain.