pigmented colorants: dependence on media and time - Cornell ...

appearance. Reflection can also mirror-like, or specular, as in metallic surfaces.
Materials can also maintain a combination of both types of reflected light, as in
glossy materials like plastic. In all cases, an incident light ray hits a surface and
is reflected. The angle of which the ray is reflected is equal and opposite to the
angle between the incident light ray and the normal (the ray perpendicular to the
surface). It is the surface definition that determines the amount and direction
of reflected light. Smooth surfaces have aligned normals, hence the reflection is
mirror-like; rough surfaces have randomly-orientated normals and thus scatter the
light.
In Figure 2.11, an incoming light ray i is reflected as ray r. At the point where
the light strikes the surface, the normal n defines the direction perpendicular to
the surface. The incident ray is reflected such that the angle of incidence, θi, is
equal to the angle of reflection, θr.
Figure 2.11: As light enters a medium, it is either reflected, transmitted,
or absorbed.
We can never speak of the speed of light in the abstract, since it must always
be in respect to some medium. The most common reference is a perfect vacuum,
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