I use snow as an analogy for light here.
If you live where it snows, imagine stepping outside after the first snowfall of winter.
The snow makes your neighborhood look different.
You notice different things than you would have without the snow.
Note how the snow on the bolder below changes how it looks.
The lighting, the snow, makes the surface of rock more apparent.
Sunlight, coming from the side, would do the same, by creating shadows.
But, we may not notice the effect of lighting as much as we would the effect of a dusting of snow.