Plastics Technology Laboratories  

Index of Refraction of Transparent Organic Plastics
(Refractive Index)


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The index of refraction is the ratio of the velocity of light in a vacuum to the velocity of light in a transparent material. The index of refraction can be used to calculate the bend angle of a beam of light as it passes from one transparent medium to another. Thus, the index of refraction is used in designing optical lenses and as a quality control check of transparent plastics.

Test Procedure:
A small drop of contacting liquid is placed on the center of the prism, then the test sample is placed on the prism. The light source, index arm, and compensator drum are adjusted to align the sample through the eyepiece. The refractometer will then provide a digital read-out of the refractive index.

Specimen size:
Any size that provides a flat polished surface that will sit on the refractometer prism. Typically, 6.3 x 12.7 mm on one face is sufficient.

Index of Refraction

Equipment Used:
Dual amici prism compensator @ 589nm (Sodium D Line) illumination

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**Please note that this test description is intentionally generic in nature and aimed at providing a descriptive summary to enhance test understanding. For more information please contact a Intertek PTL Technical Representative at . Due to copyright restrictions, we are not able to provide copies of standards. Standards can be obtained from appropriate standards authorities.

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