Reflection

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Transmission of light through a medium is decreased by any absorption that may be present. In addition to absorption, the amount of transmitted light can be reduced by surface reflection. The word reflection comes from the Latin word reflectere, which means to bend back. Reflection is a surface or boundary phenomenon. In general, whenever light is incident on a surface or a boundary between two different mediums, some of the incident light is reflected or bent back. The percent of the light reflected, and the wavelength dependence of that percentage, depends on the materials involved and the angle of incidence of the incident light. On a molecular level, the reflection process involves an interaction of the incident light with the electrons in the atoms and molecules of the surface layers. There is a connection between a material's absorption properties and its reflection properties. Strong absorbers, such as metals, are strong reflectors. Weak absorbers, such as water and clear glass, are weak reflectors. Reflection is classified as either specular or diffuse. The word specular means mirror-like. Specular reflection occurs when the surface is smooth and is the reflection involved in the formation of images by mirrors or other smooth surfaces such as a pond of water. Diffuse reflection occurs when the surface is rough. The law of reflection states that the angle of reflection θr is equal to the angle of incidence θi, or mathematically, θr = θi.