Polarization and Malus's law simulator

Light is a transverse wave, so its electric field has a direction. A polarizer passes one direction and blocks the one perpendicular to it.

Malus's law

Linearly polarized light of intensity I₀ passing through a polarizer at angle θ to its polarization emerges with I = I₀ cos²θ. At 0° everything passes, at 90° nothing does.

The three-polarizer surprise

Two crossed polarizers (0° and 90°) block all light. Insert a third at 45° between them and light comes through: unpolarized input is halved by the first polarizer, then multiplied by cos²45° = ½ twice more, leaving 1/8 of the original intensity.

Why it works

Each polarizer projects the light onto a new axis, so the middle polarizer gives the field a component along the final axis that it did not have before.

Try it

Open the 3D scene, rotate a polarizer, and watch the transmitted intensity follow cos²θ.