Plastic has a colour associated with diffusely reflected light, but the specular component is uncoloured, most materials fall into this category. Define the R, G, B reflectance values and the specularity and roughness (the name ‘plastic’ should not be interpreted as referring to plastic objects). The reflectance values have the range 0.0 to 1.0 (although 0.0 and 1.0 do not occur in nature). Sometimes for a given surface a single reflectance value is given – this probably refers to the average hemispherical reflectance; where you are only interested in illuminance this single value can be used for each of the R, G and B values. Specularity also has the range 0.0 to 1.0, 0.0 for a perfectly diffuse surface and 1.0 for a perfect mirror. In reality plastic materials are generally not very reflective and the specularity value is usually in the range 0.0 – 0.07. Roughness, with the same limits, refers to how the surface scatters what light is reflected, 0.0 meaning perfectly smooth. Plastic materials generally have a roughness in the range 0.0 – 0.02.
