Specular reflection
[2] Later, Alhazen gave a complete statement of the law of reflection.
Optical processes, which comprise reflection and refraction, are expressed by the difference of the refractive index on both sides of the boundary, whereas reflectance and absorption are the real and imaginary parts of the response due to the electronic structure of the material.
[8] The degree of participation of each of these processes in the transmission is a function of the frequency, or wavelength, of the light, its polarization, and its angle of incidence.
A surface built from a non-absorbing powder, such as plaster, can be a nearly perfect diffuser, whereas polished metallic objects can specularly reflect light very efficiently.
Light propagates in space as a wave front of electromagnetic fields.
When a ray encounters a surface, the angle that the wave normal makes with respect to the surface normal is called the angle of incidence and the plane defined by both directions is the plane of incidence.
When the light is incident perpendicularly to the surface, it is reflected straight back in the source direction.
The phenomenon of reflection arises from the diffraction of a plane wave on a flat boundary.
Assuming these Euclidean vectors are represented in column form, the equation can be equivalently expressed as a matrix-vector multiplication:[11] where
It is a function of the wavelength of radiation, and is related to the refractive index of the material as expressed by Fresnel's equations.Hecht, Eugene (1987).
ISBN 0-201-11609-X. In regions of the electromagnetic spectrum in which absorption by the material is significant, it is related to the electronic absorption spectrum through the imaginary component of the complex refractive index.
The electronic absorption spectrum of an opaque material, which is difficult or impossible to measure directly, may therefore be indirectly determined from the reflection spectrum by a Kramers-Kronig transform.
The polarization of the reflected light depends on the symmetry of the arrangement of the incident probing light with respect to the absorbing transitions dipole moments in the material.
Lower quality measurements using a glossmeter quantify the glossy appearance of a surface in gloss units.
If a flat mirror is mounted on the ceiling it can appear to reverse up and down if a person stands under it and looks up at it.
More specifically a mirror changes the handedness of the coordinate system, one axis of the coordinate system appears to be reversed, and the chirality of the image may change.
The measurement technique of x-ray reflectivity exploits specular reflectivity to study thin films and interfaces with sub-nanometer resolution, using either modern laboratory sources or synchrotron x-rays.
