Materials and light I: Reflection

Technical Report

I think I should start slowly, dealing elementary questions about light and architecture. Some readers may regret about that because I start at an elementary level, or maybe because I'm providing a very technical approach to a matter as poetic as light and architecture ... But I must start somewhere.
The first issue I would like to make corresponding to the study of materials and their behavior under the effect of light. As many readers know, the light (either from the sky or a light bulb, a light source in any case) incident on a surface and it is reflected. Thanks to the reflection of light, photons reach our eyes and we are able to identify an object.
The objects can reflect light in many ways. When light falls on a surface it can be reflected in all directions, creating a diffuse reflection or it can be reflected in one direction, creating a specular reflection. This property is defined as reflection of the material. 
Reflection directly depends on the roughness of the surface where the light impact. It really is that simple. When the surface is completely smooth, the incident light is reflected at the same angle of incidence. This is called specular reflection:

Therefore, in the specular reflections we can see the perfect reflection of your face in a mirror or the sky in a building:

The composed reflection is similar to specular, with the difference that part of the light is scattered due to surface roughness:

This reflection is seen in brushed metals, where the roughness is homogeneous:

Diffuse reflection occurs when the light incident on a surface is reflected in all directions, where the ray perpendicular to the surface reaches the greatest intensity:

In diffuse reflection, the angle of the incident light is completely irrelevant. The diffuse reflection is also called Lambertian reflection. It is seen in very rough materials:

Finally, there is a fourth type of reflection, called mixed. It is typical of heterogeneous materials with varying finishes, where there are areas very rough with others polished:

The mixed reflection can be observed in granite, some types of marble, such as travertine, and varnished wood:

With this brief introduction we have seen how the roughness of a surface may affect the reflection of light, hence it is very decisive aspect in the field of illumination. Soon I will expose a further report on qualities of the materials, the reflectance.

See ASAP.