Here's why:

* Luminous objects: These objects produce their own light. Examples include the sun, stars, light bulbs, and fireflies.

* Non-luminous objects: These objects do not produce their own light. They can only be seen because they reflect light from a luminous source. Stones, like most objects around us, fall into this category.

We can see stones because light from the sun or another light source bounces off their surface and reaches our eyes.