What is a Polarizer?

Josie Myers

A polarizer changes electromagnetic energy, such as visisble light, from a mixed, or unpolarized beam into a single polarized beam. Many optical instruments like cameras, telescopes, and microscopes use this technology as either integrated or screw-on devices to view specific types of light. There are two general kinds of polarizers: absorptive and beam splitting.

Polarized sunglasses, which are made with an absorptive polarizer film.
Polarized sunglasses, which are made with an absorptive polarizer film.

An absorptive polarizer filters out the unwanted beams by absorbing them, and leaves behind just the desirable ones. The most common type of absorptive filter is a wire grid, which allows only a single type of beam to pass through. Polaroid™is one of the most popular name brands of absorptive polarizer, as it uses stretched polyvinyl alcohol polymer chains to filter light. The famous, but now-obsolete, instant picture film used the technology, and it is still in use as a film for sunglasses, liquid crystal displays, and microscopes.

Reflected polarized light is useful for studying silicon wafers.
Reflected polarized light is useful for studying silicon wafers.

A beam-splitting polarizer does just what it's name says, in that it splits a beam into two opposing polarizations. Much like a magnet has a positive and negative end, so does a beam of light, although the difference is not quite so easily understood. The polarization of light through beam splitting will generally produce one pure beam and one mixed beam, rather than two pure beams.

Telescopes usually have polarizing technology.
Telescopes usually have polarizing technology.

The most commonplace usage of a polarizer is in photography. A lens attachment reduces reflections, and increases the saturation of color. The contrast between clouds and sky is more prominent, and details like leaves tend to look crisper when using a polarizer. A polarizer is most effective when shooting at an angle 90% from the sun. It is not effective for a photographer to shoot with the sun at his back.

Astronomers use polarizing filters with their telescope eyepieces to focus on a celestial object. The filter reduces glare without altering the true color of the object being viewed. This glare reduction allows for a clearer view of the object, and the ability to see more terrain details and anomalies.

Microscopes also use polarizers to study various materials. A polarizing microscope uses two types of filters, a polarizer situated beneath the specimen, and an analyzer situated above. With the specimen between the two, a light free environment is made possible. The analyzer can be moved into or out the field of view to give an observer various levels of polarization. The technology permits the viewing of either reflected or transmitted light. Reflected polarized light is particularly useful for studying mineral oxides and sulfides, silicon wafers, and metals.

Polarizing sunglasses filter out unwanted beams by absorbing them.
Polarizing sunglasses filter out unwanted beams by absorbing them.

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Discussion Comments


@miriam98 - You can buy a polarizer film filter for your telescope just like you can with your regular digital camera. It works the same way.

It would be very useful as you're doing your stargazing where there are a lot of nearby city lights. The filter will cut out the glare from those lights and let you clearly see the objects in the night sky.


@hamje32 - The point in either case is to reduce the glare from the sun. As the article says the absorptive filter does that quite well.

I remember I went to get new prescription glasses last year. They put some dye or some stuff in my eye as part of the eye exam. They told me the stuff would wear off in a few hours, but that I would have to be careful driving.

They gave me some special sunglasses that I think had the filter on them, because it did a very good job of absorbing sunlight. I drove home with it.

Just out of curiosity, I removed them temporarily when I got home and it felt like I was being blinded by the sun. Clearly the filter had been doing a very good job, so I left the glasses on for an hour or more until the medicine they gave me wore off.


@SkyWhisperer - I think you’re describing the effects of a circular polarizer filter. I didn’t start out with one of those. I started with a neutral density filter, because that works to cut outdoor light too.

The only problem with the neutral density filter is that it tends to make everything dark, depending on the intensity of the filter. The polarizer is much more subtle in its effect. I’ll have to get that sometime and see how it works for me.


I bought a 52mm polarizer for my digital camera. It’s one of the few filters that I have actually; the other one is a UV filter.

Honestly, I am surprised that I waited so long to get that polarizer. It did wonders for my outdoor photography. The blue sky was much bluer and it cut out some of the glare from the sun on reflective surfaces like metal and water.

In the end, it made for much more saturated, richer photos. I highly recommend that you get one if you have not done so. Really I don’t recommend that you go overboard in filters, but anything that will cut down your light by a few “f stops” (as they’re called) will do you well, especially with outdoor photography.

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