Light travels in straight lines at approximately 186.000 miles per second through air or vacuum and is clear. If a beam of light shines onto a surface, it will be wholly or partly reflected. Light meeting a smooth and level surface at a certain angle will leave it at a similar angle, angle of incidence is equal to angle of reflection (the snooker ball bounces off the cushion at the same angle at which it is hit).

By surface, we mean the boundary between two different types of substance light will reflect from the bottom face as well as the top face of a plate of glass since both are glass/air boundaries. From a perfectly smooth paint film, light from an object is reflected uniformly to the eye of the observer since the eye receives a complete picture of the object, the observer sees it in sharp outline and the film looks glossy.

If the surface is not smooth, parts of the object can be seen clearly by reflection, but parts are lost since the light is scattered, the overall result is a blurred picture and the observer perceives low gloss.

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