Malus Law Calculator
Use our Malus law calculator to calculate transmitted light intensity through a polarizer from initial intensity and angle of incidence. Includes the Malus law formula, a worked example, and an explanation of what Malus law means in physics.
Malus Law Explained
Malus law describes how the intensity of polarized light changes after passing through a polarizing filter (analyzer).
When linearly polarized light passes through an analyzer at an angle θ relative to the light’s polarization direction, the transmitted intensity decreases according to a cosine-squared relationship.
This Malus law calculator uses initial intensity (I₀) in W/ft² and angle θ in degrees to return the transmitted intensity (W/ft²).
Malus Law Formula
Transmitted intensity equals initial intensity times cos²(θ).
θ is the angle between the polarization direction of the incident light and the analyzer axis.
At 90°, cos(90°)=0, so transmitted intensity is 0.
How to Calculate Malus Law
- 1
Enter the initial intensity (I₀) in W/ft².
- 2
Enter the angle of incidence (θ) in degrees.
- 3
The calculator applies I = I₀ × cos²(θ) to return intensity (W/ft²).
Frequently Asked Questions
Malus law states that the intensity of polarized light after passing through a polarizer is I = I₀ cos²(θ), where θ is the angle between the light’s polarization and the polarizer axis.
I = I₀ × cos²(θ).
The transmitted electric field component scales with cos(θ), and intensity is proportional to the square of the field amplitude, giving cos²(θ).
Malus refers to Étienne-Louis Malus, who studied polarization and is associated with the law describing intensity changes through polarizers.
Malus law describes already linearly polarized light passing through an analyzer. Unpolarized light first becomes polarized by a polarizer, typically reducing intensity before Malus law is applied for a second polarizer.