Lens Index Calculator

Formula

To calculate the lens index (\(LI\)):

\[ LI = \frac{d}{r} \]

Where:

\(LI\) is the lens index
\(d\) is the thickness of the lens (mm)
\(r\) is the radius of curvature of the lens (mm)

What is a Lens Index?

A lens index refers to the refractive power of a lens, which is its ability to bend light. It is a number that describes how thick or thin the lens is in relation to its degree of vision correction. A higher index means a thinner, lighter lens, which is beneficial for those with stronger prescriptions. Common lens indices range from 1.50, for standard plastic lenses, to 1.74, for the thinnest and lightest lenses available.

Example Calculation 1

Let's assume the following values:

Thickness of the lens (\(d\)) = 2.0 mm
Radius of curvature of the lens (\(r\)) = 10.0 mm

Using the formula:

\[ LI = \frac{2.0}{10.0} = 0.2 \]

The lens index is 0.2.

Example Calculation 2

Let's assume the following values:

Thickness of the lens (\(d\)) = 1.5 mm
Radius of curvature of the lens (\(r\)) = 8.0 mm

Using the formula:

\[ LI = \frac{1.5}{8.0} = 0.1875 \]

The lens index is 0.1875.