<P> There are many special rays that are used in optical modelling to analyze an optical system . These are defined and described below, grouped by the type of system they are used to model . </P> <Ul> <Li> An incident ray is a ray of light that strikes a surface . The angle between this ray and the perpendicular or normal to the surface is the angle of incidence . </Li> <Li> The reflected ray corresponding to a given incident ray, is the ray that represents the light reflected by the surface . The angle between the surface normal and the reflected ray is known as the angle of reflection . The Law of Reflection says that for a specular (non-scattering) surface, the angle of reflection always equals the angle of incidence . </Li> <Li> The refracted ray or transmitted ray corresponding to a given incident ray represents the light that is transmitted through the surface . The angle between this ray and the normal is known as the angle of refraction, and it is given by Snell's Law . Conservation of energy requires that the power in the incident ray must equal the sum of the power in the refracted ray, the power in the reflected ray, and any power absorbed at the surface . </Li> <Li> If the material is birefringent, the refracted ray may split into ordinary and extraordinary rays, which experience different indexes of refraction when passing through the birefringent material . </Li> </Ul> <Li> An incident ray is a ray of light that strikes a surface . The angle between this ray and the perpendicular or normal to the surface is the angle of incidence . </Li> <Li> The reflected ray corresponding to a given incident ray, is the ray that represents the light reflected by the surface . The angle between the surface normal and the reflected ray is known as the angle of reflection . The Law of Reflection says that for a specular (non-scattering) surface, the angle of reflection always equals the angle of incidence . </Li>

When light rays from an object are incident
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