When light obeys the law of reflection, it is termed a specular reflection. Even transparent glass specularly reflects a portion of incoming light. Diffuse reflection is typical of particulate substances like powders. If you shine a light on baking flour, for example, you will not see a directionally shiny component. The powder will appear uniformly bright from every direction.
Many reflections are a combination of both diffuse and specular components.
One manifestation of this is a spread reflection, which has a dominant directional component that is partially diffused by surface irregularities. Bouger s law states the logarithmic relationship between internal transmission at a given wavelength and thickness. Find the external transmittance T 2.2 for a filter that is 2.2 mm thick. When light passes between dissimilar materials, the rays bend and change velocity slightly, an effect called refraction. The index of refraction itself is also dependent on wavelength.