Enter the incident optical intensity and the transmitted optical intensity into the calculator to determine the optical density.

Optical Density Formula

The following formula is used to calculate the optical density.

OD = log(I_0 / I ) 
  • Where OD is the optical density
  • I0 is the incident optical intensity (optical intensity hitting the material)
  • I is the transmitted optical intensity (optical intensity transmitted by the material/film.

To calculate optical density, take the log of the incident optical intensity divide by the transmitted optical intensity.

Optical Density Definition

An optical density is defined as the total optical attenuation per centimeter of material. Optical attenuation is the loss or amount of optical light that material retains as it travels over or through a medium.

How to calculate Optical Density?

Example Problem #1:

First, determine the incident optical intensity. For this problem, the incident optical intensity is measured as 1500 units.

Next, determine the transmitted optical intensity. This is measured to be 150 units.

Finally, calculate the optical density using the formula:

OD = log10 (I0 / I )

= log10 (1500/ 150 )

= 1.

Example Problem #2:

In this next problem, the incident optical intensity is now 3000 units and the transmitted intensity is now 500 units.

Using the same formula as above:

OD = log10 (3000/500)

= .7781

optical density calculator