What Is a Linear Polarizer?

Andrew Kirmayer

A linear polarizer is often used in sunglasses, camera lenses, projection filters and other materials to allow light waves, traveling in a certain plane, to pass through it. Light typically loses about half of its intensity by the time it reaches the other side of an object. It can also be oriented in horizontal or vertical positions, or other angles in between, through linear polarization depending on the angle of the polarizer. The device can be used to minimize reflections, control light intensity, or eliminate light such to make colors more vibrant. Various kinds of linear polarizer are available, including dichroic, reflection, double refraction, and beamsplitting polarizers.

Linear polarizers are often used in sunglasses.
Linear polarizers are often used in sunglasses.

The characteristics that generally define a linear polarizer are its transmitting and absorbing abilities. A transmitting axis, which often varies based on the polarizer’s grade, is what determines how much light can pass through. The absorbing axis does not allow light to get past the barrier. Two polarizers can be used at 90° angles to one another so that no light gets through to the other side.

Dichroic polarizers can absorb polarized light waves oriented in a particular direction. Such linear polarizer varieties can be made of polyvinyl alcohol or a laminated polymer film. When placed in between anti-reflection glass, they can be used for applications using infrared light. Reflection polarizers work by reflecting unpolarized light off of a smooth surface, which is usually non-metallic. The level of polarization can vary based on how the surface refracts the light and at what angle it is reflected from the device.

A double refraction linear polarizer can split one beam of light into two. Both of these beams are generally the same intensity, which is often accomplished by quartz and other crystals that are found in the environment. A beamsplitting polarizer similarly creates two linearly polarized beams of light. One beam continues in a straight line while the other is directed in the perpendicular direction to the other. Most polarizers are generally offered in various sizes depending on what they are used for.

Often, a linear polarizer can be used to cancel out reflections off of water. It can also increase color saturation, which is useful for decreasing the effect of reflections created by atmospheric effects like haze. A linear polarizer can also be used in the light filter of a camera or production machinery used for imaging applications. It can also be used to simulate animation by incorporating multiple axes to create an effect of motion.

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