Transparency (optics)

In optics, transparency is the property of allowing light to pass. Transparent materials can be seen through; that is, they allow clear images to pass. The opposite property is opacity. Translucent materials allow light to pass through them only diffusely, that is, the material blurs the image.

Transparency

Though transparency usually refers to visible light in common usage, it can actually refer to any type of radiation. For example, flesh is transparent to X-rays, while bone is not, allowing the use of medical X-ray machines.

Examples of transparent materials are air and some other gases, liquids such as water, most glasses, and plastics such as Perspex. Where the degree of transparency varies according to the wavelength of the light, the image seen through the material is tinted. This may for instance be due to certain metallic oxide molecules in glass, or larger colored particles, as in a thin smoke. If many such particles are present the material may become opaque, as in a thick smoke.

From electro-dynamics it results that only a vacuum is really transparent in the strict meaning, any matter has a certain absorption for electro-magnetic waves.

There are transparent glass walls that can be made opaque by the press of a button, a technology known as electrochromics.

Certain crystals are transparent because there are straight lines through the crystal structure. Light passes unobstructed along these lines.

There is a complicated theory "predicting" (calculating) absorption and its spectral dependence of different materials. See: absorption (optics) - absorption of photons by a material and Absorption spectroscopy.

Translucency

Examples of translucent materials are frosted glass, paper, and some kinds of amber. Opacity is based either on absorption or on reflection of the light falling onto the material.

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Transparency

Translucency

See also