Transmittance

What is this formula?

Transmittance is the fraction of incident light that passes through a sample. It is one of the fundamental quantities measured in spectrophotometry and serves as the basis for calculating absorbance.

When to use it

Use this formula when analyzing how much light is transmitted through a solution, optical filter, biological sample, or transparent material.

Example

A spectrophotometer measures:

Incident intensity:

I0 = 100 units

Transmitted intensity:

I = 25 units

Formula:

T = I/I0

Substitution:

T = 25/100

Result:

T = 0.25

The sample transmits 25% of the incident light.

Applications

- UV-Visible spectrophotometry

- Optical filter characterization

- Water quality analysis

- Pharmaceutical testing

- Biochemical measurements

- Material transparency studies

Note

Transmittance is a dimensionless ratio ranging from 0 to 1. It is directly related to absorbance through the logarithmic relationship A = -log(T). Highly absorbing samples produce low transmittance values.