How much light passes through three ideal polarizers at 0°, 45° and 90°?

For initially unpolarized light, one eighth of the input power is transmitted. The first sheet halves the power and each following 45° relative step halves it again.

Does a polarizer change the light color?

The ideal linear polarizer here changes polarization and power, not wavelength. Its effect is different from a wavelength-selective color filter.

Are the placement angle and polarization axis the same control?

No. Placement sets where the ray hits the sheet. The transmission-axis control describes the selected polarization in the stated s/p convention.

What does the PBS transmit?

This ideal PBS transmits s and reflects p. Its output powers add to the incident power.

Does this include circular camera polarizers?

No. It includes ideal linear polarizers and a PBS, not a quarter-wave plate or a complete camera CPL assembly.

Is polarization defined when the detector receives no light?

No. The panel reports no signal rather than assigning a measured polarization to zero power.

Polarizing Filter Simulator: Malus Law and Three Polarizers

What does a polarizing filter do?

A linear polarizer selects an electric-field orientation. It is different from a color filter: changing polarization does not require changing wavelength. In this ideal model, the selected component is transmitted and the rejected component is absorbed.

For unpolarized incident light, an ideal first polarizer transmits half the power. For linearly polarized light meeting a polarizer at relative angle θ, Malus' law gives I = I₀ cos² θ. Here I₀ is the power immediately before that polarizer. Reference: Edmund Optics on polarization and Malus' law.

Try the three-polarizer experiment

Leave the incident polarization set to Unpolarized.
Keep the first and last sheets at 0° and 90°.
Turn off Include middle polarizer. The crossed pair blocks the ideal beam.
Turn the middle sheet back on and set its axis to 45°. The detector should receive 0.125 power units.
Change the middle angle and compare the result, or select Linear incident polarization to explore a different input.

The source and screens stay in fixed positions in this explanation page. Free lab lets you move the components, change the physical placement angles and set each polarizer's transmission axis independently.

Why does adding a sheet let light through?

The first sheet prepares a linearly polarized output. With no middle sheet, the final axis is perpendicular to it and the transmitted power is zero. With a 45° middle sheet, the polarization is selected again before reaching the final sheet.

For a one-unit unpolarized source, the first sheet leaves 1/2, the middle sheet leaves 1/4, and the final sheet leaves 1/8. The absorbed amounts plus the detected output still add to one. Adding the middle component has changed which polarization reaches the last component; it has not created energy.

At a middle angle of 30°, the expected output is 0.5 × cos²30° × cos²60° = 0.09375. If you start with a one-unit beam already polarized along the first sheet, its first transmission is one rather than one half. Always state the incident polarization when comparing measurements.

How are the angles defined in a two-dimensional drawing?

In this model, 0° refers to s polarization, perpendicular to the drawing plane. 90° refers to p polarization, inside the drawing plane and transverse to the ray. A sheet's transmission axis is a separate setting from its geometric placement angle. For oblique incidence the axis is projected into the ray's transverse basis.

The normal-incidence preset gives the simple Malus-law demonstration. The model does not include the detailed angular response, coatings or finite extinction ratio of a manufactured film. Ideal mirrors use a stated perfect-reflector phase convention, while the new glass guide uses Fresnel amplitudes and TIR phase. Separate ray paths are not summed as coherent fields.

Compare a polarizing beam splitter

Choose Polarizing beam splitter in the Experiment selector. This ideal PBS transmits the s component and reflects the p component into a second route. Unpolarized input produces two half-power outputs, each with a definite polarization. Choosing a purely s-polarized source sends the power into the transmitted output.

Use Detector readout to inspect either output. An ordinary nonpolarizing splitter divides both polarization components by its chosen ratio; the PBS sorts them instead. It does not sort red from blue, and it does not send full input power down both branches.

Is this the same as a camera CPL filter?

The components here are ideal linear polarizers and a PBS. A camera circular polarizing filter generally combines linear polarization selection with a retardation element. A quarter-wave plate and a complete camera-filter assembly are not components of this release.

Searching for polarizing filters often leads to photography shopping advice. This page focuses on a physics experiment and wavelength-resolved power readings, not product recommendations for a camera lens. The spectral detector shows that the ideal sheets can change intensity while leaving the source's wavelength support unchanged.

Measurement and model limits

The source contains 27 wavelength samples. The graph exposes their individual powers and the detector's polarization degree. A zero-signal detector has no defined measured polarization. Real detector noise, calibration and a physical polarimeter's response are not modeled.

Try combining these tools with a glass light guide or a diffraction grating in Free lab. These experiments do not change the formal campaign count or consume walkthrough credits.