Difference Between Optical Density & Absorbance

By Samuel Markings
Pure laser light is a useful tool in scientific research, industry and medicine.
Kim Steele/Digital Vision/Getty Images

Optical devices play a major role in modern-day technologies and can be found in CD players, DVD players and fiber-optic cable boxes. Optical density and absorbance both measure the amount of light that is "absorbed" when passing through an optical component, but there is a subtle difference between the two terms.

Optical Density Vs Absorbance

Optical density is the amount of attenuation -- or gradual intensity loss -- that occurs when light passes through an optical component, such as a neutral density filter. Mathematically, optical density is equal to :

OD = Log (Power transmission factor)

For example, an optical density of 3 attenuates the light power by a factor of 10^3 (1,000). Optical attenuation may result from not only absorption of light but also from scattering of light. Absorbance considers only absorption within the optical component.

About the Author

Samuel Markings has been writing for scientific publications for more than 10 years, and has published articles in journals such as "Nature." He is an expert in solid-state physics, and during the day is a researcher at a Russell Group U.K. university.