Eyesight

Our eye is a "light receiver". Shining objects emit light which falls into our eyes - that is why we can see them. In the picture below, light is emitted by a candle. It emits its light in all directions. The red arrows in the picture indicate that some part of the light also hits the eyes of the observer.

But we are also able to see objects which do not shine themselves but which are illuminated by shining bodies. The light emitted by the candle hits a piece of paper in the picture below. But part of the light is reflected by the piece of paper in all directions (people say the light is scattered). A small part of the light again enters the the eye of our observer - he can see the piece of paper therefore. The path of the light from the candle to the piece of paper is marked by the red arrows.