Lei Malus
- Created by
- Renato Passos, Eng. de Software
- Reviewed by
- Renato Passos, Eng. de Software
Last updated: Apr 18, 2026
About this calculator
The Polarization by Malus's Law Calculator determines the intensity of light transmitted through a polarizer, based on the initial intensity and the angle between the polarizer's axis and the light's polarization direction. The formula I = I₀·cos²θ expresses this relationship, where I₀ is the initial intensity, θ is the angle, and I is the transmitted intensity. This tool is useful in optics experiments and the design of systems using polarized light.
To use the calculator, enter the initial light intensity (I₀) and the angle θ in degrees. The result is the transmitted intensity (I) after passing through the polarizer. Malus's law is valid only for linearly polarized light. In real-world situations, such as polarized sunglasses or photographic filters, the alignment angle between the filter and the light directly affects how much light passes through.
An important caution: the formula assumes an ideal polarizer with no losses or absorption. Real polarizers may have additional intensity reduction. Also, the angle must be correctly measured between the light's polarization direction and the polarizer's axis. This calculator is especially useful in physics labs, optics classes, and engineering projects involving light control.
Use cases include educational experiments to demonstrate polarization, calibration of optical equipment, and simulation of effects in fiber optic communication systems. Remember that Malus's law describes only the polarized component; if the light is partially polarized, the transmitted intensity will have an additional contribution from the unpolarized component.
Frequently asked questions
What is Malus's Law?
It is a law that describes the intensity of light transmitted through an ideal polarizer, given by I = I₀·cos²θ, where θ is the angle between the light's polarization direction and the polarizer axis.
Does this calculator work for unpolarized light?
No. Malus's Law applies only to linearly polarized light. For unpolarized light, the transmitted intensity through an ideal polarizer is half the initial intensity, regardless of angle.
Should the angle be in degrees or radians?
The calculator expects the angle in degrees. It internally converts to radians for the calculation, so enter the value in degrees.
What are the units of intensity?
The units are relative. You can use any consistent unit (like W/m²), as long as I₀ and I are in the same unit. The result will have the same unit as I₀.
What does I = 0 mean?
When I = 0, it means the angle θ is 90° or 270°, i.e., the polarizer axis is perpendicular to the light's polarization direction, blocking all light.