Sight

Our eyes are light collectors. Glowing objects emit light that is collected by our eyes - and this is why we can see. In the image below light is emitted by a burning candle. It emits light in every 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 in the image below. Parts of the light are reflected by the paper in all directions (we call this "diffusion"). Some parts of the reflected light hit the eye of the observer - so they are able to see the paper. The path of the rays of light from the candle over the piece of paper into the eye is illustrated with red arrows.