IOR

IOR, or index of refraction, is a dimensionless quantity that describes how light propagates through a medium. It is defined as n = c / v, where c is the speed of light in vacuum and v is the phase velocity of light in the medium. The refractive index governs how light bends at interfaces via Snell's law (n1 sin θ1 = n2 sin θ2). In most materials, n depends on wavelength, a phenomenon called dispersion; the index can also be complex, n = n − i k, where k is the extinction coefficient that accounts for absorption.

Common values are illustrative but not universal: air is about 1.0003, water around 1.333, typical crown glass near 1.5, and diamond near 2.4. Some materials are birefringent, having different refractive indices along different crystallographic directions, producing ordinary and extraordinary indices.

Applications of the IOR include optics design, where accurate refractive indices are essential for lenses, coatings, and waveguides. In computer graphics and rendering, IOR is a material parameter that controls the strength of refraction and, together with Fresnel equations, influences reflections and light transmission through translucent objects. Ray tracing relies on IOR to model light paths through materials.

Measurement and characterization of refractive indices can be performed with refractometry, spectroscopic ellipsometry, or other optical methods. Values are often reported for specific wavelengths or wavelength ranges, and they may vary with temperature and chemical composition.

In summary, IOR is a fundamental property used across science and engineering to describe how materials interact with light, with wide implications in both practical applications and visual simulations.