Reflexion and Diffusion

Let's take a look at an even surface (e.g. a piece of aluminium foil or a mirror) that is hit by parallel rays of light. These are reflected on the even surface and they are still parallel when leavig the mirror. Reflection on an even surfaces allows us to see images of other objects (here the observer sees the reflected image of the lamp), the reflecting surface itself is not visible.

If the reflecting surface is rough (e.g. a page of a book or a tree and so on), the incoming parallel rays of light are reflected in all possible directions. This case is called "diffuse reflection" or "diffusion". Because of diffusion we are able to see objects that do not glow themselves. Therefore, the observer does not see the reflection of the lamp but the object itself.