Fishermen see through water glare and photographers darken skies with the same trick: polarized light. Ordinary light vibrates in every direction at once, but a polarizing filter passes only the waves aligned with its axis. Malus's law says exactly how much gets through: the transmitted intensity equals the incoming intensity times the square of the cosine of the angle between them, I = I₀ × cos²θ. Align the filter with the light and nearly everything passes; rotate it to 90 degrees and the scene goes black.

This calculator runs Malus's law. Type the incoming light intensity into Variable A — use any consistent unit, like lux or milliwatts — and the value of cos²θ for your filter angle into Variable B. The Result box shows the transmitted intensity. A landscape photographer in Colorado rotating a polarizer to 30 degrees off the glare axis, for instance, enters cos²(30°) = 0.75 and learns three-quarters of the light survives. LCD screens, 3D movie glasses, and beekeepers' veil-free observation hives all lean on this same cosine-squared rule.

With the pre-filled defaults — Variable A 10, Variable B 5 — the Polarization Calculator returns Result 50.0000. Change any input and those results update instantly, so you can see exactly how each number you enter moves the answer.