Not just mirrors

Reflection from any surface

The law of reflection describes reflection of light from any surface, not just the shiny ones of mirrors, glass windows and polished cars.

Each point on a stone wall reflects light. For each point the angle of incidence equals the angle of reflection. Picture lots of tiny pieces of the wall's surface, reflecting like tiny mirrors. But the pieces either side are not all lined up. The stone is rough, not smooth.

Reflection like this is called diffuse reflection. You see most of the things in your environment by diffuse relfection.

Paint and reflections

People can make paint so that the surfaces are reflective in different ways to create different moods.

For gloss paint the particles at the surface of the paint are very small and when the paint dries they end up making a very smooth surface which acts just like a mirror. Any light shining onto this surface is reflected regularly and it may be possible to see the image of an object (your face!) as light is reflected.

Use a microscope to look at the surface of dry matt paint, and it looks like a pebble beach. Light reflected from each small part of a pebble is described by the law of reflection. But because the small parts are not lined up the overall effect is that the light is scattered in all directions. Our eyes detect light from parts of many different pebbles so it looks like diffuse reflection.


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