Polarized light vibrates in one direction across its path, instead of in every direction. A polarizing filter passes only the light that vibrates along its own direction.
In more detail
Two filters at right angles (crossed) pass no light, unless something between them changes the light. Many phone and laptop screens give out polarized light. So never test a polariscope or dichroscope against a screen.
How we measure it
The Polariscope models ideal polarizers by Jones calculus. Our light-performance tools average Fresnel losses over polarization. Only the simulator's render follows polarization from bounce to bounce, in doubly refractive stones.
Related terms
- Polariscope: A polariscope is a gem-testing instrument with a stone between two polarizing filters. With the filters crossed, it shows whether a stone is singly refractive, doubly refractive, strained or an aggregate.
- Doubly refractive: A doubly refractive stone splits light into two rays that vibrate at right angles and travel at different speeds. Each ray has its own refractive index.
- Jones calculus: Jones calculus is a matrix method for following polarized light through filters, retarders and crystals. R.C. Jones published it in 1941.
- Fresnel reflection: Fresnel reflection is the share of light that a surface reflects instead of letting through. The Fresnel equations give that share from the two refractive indices, the angle and the polarization.