Sight

Our eyes are light collectors. Glowing objects emit light that is collected by our eyes. Thus, we are able to see. In the image below light is emitted by a burning candle. It emits the light in very possible direction. The red arrows in the image illustrate that some rays of light hit the eye of the observer.

However, we are still able to see objects that do not glow themselves but are illuminated by other objects. The light emitted by the candle hits the piece of paper. Parts of the light are reflected by the paper in all directions (diffusion). Some parts of the reflected light hit the eye of the observer - he or she is able to see the paper. The path of the rays of light are illustrated with red arrows.