Refraction Index

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Refraction index or refraction number

Characteristics of light

For many applications of plastics, their optical properties are of particular importance. The metrological basis for test methods with which such properties can be quantitatively recorded is based on the fundamentals of geometric optics (also known as rays optics). Here, properties of light such as reflection, refraction and dispersion are examined.

Optical refraction and light reflection

When a light ray falls on the interface between two transparent media, part of it is generally reflected and part of it is refracted. Both rays travel in the plane of incidence. The angle of reflection α_R is equal to the angle of incidence α₁. The following relationship applies to the angle of refraction α₂ (Fig. 1) (Eq. 1):

$n_{2}\cdot \sin \alpha _{2}=n_{1}\cdot \sin \alpha _{1}$

(1)

Fig. 1:

Optical refraction and reflection at a flat interface

n₁ and n₂ are the index of refraction of the media in which the incident and refracted rays propagate. α₂ is the angle of refraction, α₁ is the angle of incidence. The index of refraction n is defined for each medium as the ratio between the light velocity in a vacuum and in that medium (Eq. 2):

$n={\frac {c}{v}}$

(2)

mit:

c	light velocity
v	velocity in the medium

See also

• Refraction light
• Reflection light
• Light absorption
• Light remission
• Light transmission

References

• Halliday, D., Resnick, R., Walker, J., Koch, S. (Eds.): Halliday Physik. Wiley VCH Publishing, Weinheim (2018) (ISBN 978-3-527-41356-0)
• Trempler, J.: Optische Eigenschaften. In: Grellmann, W., Seidler, S. (Eds.): Kunststoffprüfung. Carl Hanser, Munich (2025) 4th Edition, pp. 311–343 (ISBN 978-3-446-44718-9; E-Book: ISBN 978-3-446-48105-3; see AMK-Library under A 23)