Here's why:

* Natural Phenomenon: Fire is a natural phenomenon that occurs when a substance undergoes rapid combustion, releasing heat and light.

* No External Power Source: Fire doesn't rely on any external power source like electricity or batteries to produce light. It generates its own light through the chemical reaction of combustion.

* Examples in Nature: Forest fires, lightning strikes, and volcanic eruptions all produce fire and light naturally.

While we often use fire for artificial lighting, its origin and process are entirely natural.