Editing Transparency and translucency (section)

{{Short description|Property of an object or substance to transmit light with minimal scattering}}
{{Other uses of|Transparency}}
[[File:Dichroic filters.jpg|thumb|right|[[Dichroic filter]]s are created using optically transparent materials.]]

In the field of [[optics]], '''transparency''' (also called '''pellucidity''' or '''diaphaneity''') is the [[physical property]] of allowing [[light]] to pass through the material without appreciable [[light scattering by particles|scattering of light]]. On a [[macroscopic scale]] (one in which the dimensions are much larger than the wavelengths of the [[photon]]s in question), the photons can be said to follow [[Snell's law]]. '''Translucency''' (also called '''translucence''' or '''translucidity''') is the physical property of allowing light to pass through the material (with or without scattering of light). It allows light to pass through but the light does not necessarily follow Snell's law on the macroscopic scale; the photons may be scattered at either of the two interfaces, or internally, where there is a change in the index of [[refraction]]. In other words, a translucent material is made up of components with different indices of refraction. A transparent material is made up of components with a uniform index of refraction.<ref>{{cite journal |last=Thomas |first=S. M. |title=What determines whether a substance is transparent? |journal=[[Scientific American]] |date=October 21, 1999}}</ref> Transparent materials appear clear, with the overall appearance of one color, or any combination leading up to a brilliant [[spectrum]] of every color. The opposite property of translucency is [[Opacity (optics)|opacity]]. Other categories of visual appearance, related to the perception of regular or diffuse reflection and transmission of light, have been organized under the concept of [[Cesia (visual appearance)|cesia]] in an order system with three variables, including transparency, translucency and opacity among the involved aspects.

When light encounters a material, it can interact with it in several different ways. These interactions depend on the [[wavelength]] of the light and the nature of the material. Photons interact with an object by some combination of reflection, absorption and transmission.
Some materials, such as [[plate glass]] and clean [[water]], transmit much of the light that falls on them and reflect little of it; such materials are called optically transparent. Many liquids and aqueous solutions are highly transparent. Absence of structural defects (voids, cracks, etc.) and molecular structure of most liquids are mostly responsible for excellent optical transmission.

Materials that do not [[Transmittance|transmit]] light are called [[opacity (optics)|opaque]]. Many such substances have a [[chemical composition]] which includes what are referred to as [[absorption (electromagnetic radiation)|absorption]] centers. Many substances are selective in their absorption of [[Solar Light|white light]] [[frequencies]]. They absorb certain portions of the [[visible spectrum]] while reflecting others. The frequencies of the spectrum which are not absorbed are either reflected or transmitted for our physical observation. This is what gives rise to [[color]]. The attenuation of light of all frequencies and wavelengths is due to the combined mechanisms of absorption and [[Light scattering in liquids and solids|scattering]].<ref>{{cite book|author=Fox, M.|title=Optical Properties of Solids|publisher=Oxford University Press|year= 2002}}</ref>

Transparency can provide almost perfect [[camouflage]] for animals <!--or possibly military equipment?--> able to achieve it. This is easier in dimly-lit or turbid [[sea]]water than in good illumination. Many [[marine biology|marine animals]] such as [[jellyfish]] are highly transparent.

[[File:Opacity Translucency Transparency.svg|thumb|250px|right|Comparisons of 1. opacity, 2. translucency with scattering, and 3. transparency; behind each panel (from top to bottom: grey, red, white) is a star.]]