Reflection describes the return of optical radiation when it reaches a boundary between two different media. A basic distinction is drawn between diffuse and specular reflection.

Directed or specular reflection results when the roughness of the boundary is small in comparison with the wavelength of the reflected radiation. According to the law of reflection which applies in this case, the angle of the incident and reflected rays form the same angle with the normal in reference to the reflecting surface at the point of incidence.

In diffuse reflection, the returning reflection of directional incoming radiation flux is scattered in many directions. This is caused by an uneven, broken, bumpy boundary surface where the coarseness is of the same order of magnitude as the wavelength. Lambert’s cosine law applies, to a good approximation, to perfectly diffusing surfaces. This law states that the radiant intensity I at the emission angle e of a perfectly diffusing surface A of radiance L has a magnitude given by I = L · A cos θ. It follows that the radiance of a Lambertian surface is the same in all directions (isotropic). Such a completely matte white material scatters evenly in all directions, reflecting (transmitting) the radiation independently of the angle, and has a reflection factor (transmission factor) with the value 1.



Reflectance describes the relationship of the reflected radiation power (luminous flux) to the incident radiation power (luminous flux). When the reflectance is the same for all wavelengths this is known as non-selective reflectance. If the reflectance of a boundary surface depends primarily on the wavelength, or if reflection only takes place at in a very narrow range of wavelengths, the reflectance is selective.

Gigahertz-Optik offers different diffuse reflectors to be used in following typical applications:

    - Coating for integrating spheres,
    - Diffuse reflectance standards for uniformity calibration of imaging sensors or for reflectance measuring systems,
    - Large area reflectors for uniform back lighting,
    - Projection screens.


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 Additional information to download: Diffuse_Reflectors.pdf (1.1 MB)

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