Here's how it works:

* Luminous objects (like the sun, a light bulb, or a firefly) produce their own light. We can see them directly because the light they emit enters our eyes.

* Non-luminous objects, on the other hand, do not create light. Instead, they absorb some light that falls on them and reflect the rest. The light they reflect is what allows us to see them.

For example:

* A book doesn't produce its own light. When light from a lamp shines on the book, some of that light is absorbed by the book's surface, and some is reflected back. The reflected light reaches our eyes, and that's how we see the book.

The color of a non-luminous object is determined by the wavelengths of light it reflects:

* A red apple reflects primarily red wavelengths and absorbs other wavelengths.

* A green leaf reflects green wavelengths and absorbs most others.

In short, we don't see non-luminous objects directly; we see the light they reflect.