🕶️ Optical Density Calculator

Optical Density and Transmittance

Optical density (OD), also called absorbance, quantifies how much a material attenuates light. It’s defined as OD = −log₁₀(T), where T = I/I₀ is the transmittance — the ratio of transmitted intensity I to incident intensity I₀.

Because it’s a logarithmic scale, an OD of 1 means only 10% of light gets through, OD 2 means 1%, and OD 3 means 0.1%. This makes OD convenient for describing filters, laser safety eyewear, and samples that block light over many orders of magnitude.