Plastic - a plastic surface has a colour associated with diffusely reflected radiation, but the specular component is uncoloured. Most materials fall into this category – painted surfaces, wood, stone, plastic.
Metal - this material type differs from plastic in that the specular component is modified by the material colour.
Both these materials have five parameters:
1. Reflectance value for Red, 0.0 – 1.0.
2. Reflectance value for Green, 0.0 – 1.0.
3. Reflectance value for Blue, 0.0 – 1.0.
4. Specularity value, 0.0 - 1.0.
5. Roughness value, 0.0 – 1.0.
The extremes of 0.0 and 1.0 for the reflectance values do not occur in nature. Plastic materials are generally not very reflective and the specularity value is usually in the range 0.0 - 0.07. Metal materials are reflective, and the usual range is 0.5 – 1.0. Plastic materials generally have a roughness in the range 0.0 - 0.02. Metal materials have range of 0.0 – 0.5.
There are a number of different material types which can be used for window constructions (dielectric, trans, glass), with the simplest of these being glass. This is a specially modified dielectric and has a standard refractive index of 1.52 and all that needs to be defined is the transmission at normal incidence.
For definitions of dielectric, trans and glass, see the appendix.
The glass material has three parameters:
· Transmission value for Red, 0.0 - 1.0.
· Transmission value for Green, 0.0 - 1.0.
· Transmission value for Blue, 0.0 - 1.0.
The trans material has seven parameters:
· Reflectance value for Red , 0.0 - 1.0.
· Reflectance value for Green, 0.0 - 1.0.
· Reflectance value for Blue, 0.0 - 1.0.
· Specularity value, 0.0 - 1.0.
· Roughness value, 0.0 - 1.0.
· Transmission value, 0.0 - 1.0.
· Transmitted specularity value, 0.0 - 1.0.
