# Polarization of Light

How do materials polarize light? I know that they polarize light in the same plane, but light has two perpendicular directions with the two fields, so which direction is reflected and why? And if polarized glasses block the light, why can we see the road or ocean at all?

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Photographic polarizers are typically made from hardened gels with very long molecules. These molecules allow electrons to travel easily in one direction (generally along the molecules), but only with great difficulty in another. So when the oscillating electric field of light comes along, there will be two components. One, which points along the molecule, will excite the electrons, causing them to move freely. For this polarization, the molecule acts much like a metal, meaning that the light gets reflected. The other component of the light will have its electric field oscillating the wrong way; the electrons will not interact strongly with the incoming light, and will thus be unable to reflect it.

So why do you see anything through polarizers? First, polarizers are not perfect; even the best will transmit a certain percentage of the light it's supposed block. Second, and more importantly, light that you see when you look around will typically be unpolarized (or randomly polarized), which means that about half will have the polarization that should get blocked, and half will have the polarization that gets transmitted. So polarizing sunglasses do block roughly half the light (the half that happens to be randomly in the wrong polarization). Of course, if the light is reflecting off of something (especially at low glancing angles), it will typically be polarized, which is why polarizing sunglasses help to block the glare from these reflections.

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A polarizer 2D makes waves travel easily in the way of polarization, but absorbs the waves going perpendicular to the direction of polarization (turning them to heat).

This picture off wikipedia demonstrates this nicely:

When it comes to long waves like micro-waves you can use a metal plate with a few centimetres of septation, but with short waves like visible light, the polarizer must be built on the molecular level, hence you need a material with very long molecules to act as the "plates".

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