We have talked about how important color is to human beings, that we have thousands of words to describe many, many different shades of color. Color is clearly important to us; it helps us in our everyday life to be able to describe objects by their color.
So where does this concept of color come from? There a number of parts of the process that lead to you having a perception of color in your mind and what we are going to do is go through those from the beginning to the end. At the start of the whole process we have what we call an illuminant. An illuminant is a thing that emits light and the light shines on the scene, shines on the object that we are interested in and we call this incoming light, we call that the illuminance. So the illuminance is the light from the illuminant that falls on the object that we are interested in.
Now the object reflects some of that light and the light that comes from the object we refer to as the luminance, we talk about the luminance of the object. In this case we would refer to the luminance of the apple, so light is coming in from our illuminant, striking the apple, reflecting off it and entering the eye of our observer.
Some pretty amazing things happen within the eye. The incoming photons trigger a chemical reaction in the rod and cone cells at the back of your eye. They lead, in turn, to electrical impulses which are transmitted through the optic nerve to the visual cortex of your brain, which is located in the back of your head, and that leads to the perception of the color red. Which you would associate with the object you are looking at—in this case, the apple.
Where does color come from? It’s a combination of effects: the light shining on the object, how the object reflects light and the eye that observes it.