Polarization is a property of transverse waves that specifies the geometrical orientation of the oscillations). In a transverse wave, the direction of the oscillation is perpendicular to the direction of motion of the wave. Polarization is an important parameter in areas of science dealing with transverse waves, such as optics, seismology, radio, and microwaves). Light waves are transverse waves, and polarization is an important property of light.

Unpolarized light is light that is vibrating in more than one plane. Light emitted by the sun, by a lamp in the classroom, or by a candle is unpolarized light. It is possible to transform unpolarized light into polarized light. Polarized light waves are light waves in which the vibrations occur in a single plane. The process of transforming unpolarized light into polarized light is known as polarization. There are a variety of methods of polarizing light, including:

• Polarization by transmission
• Polarization by reflection
• Polarization by scattering
• Polarization by refraction

Polarization of light by use of a Polaroid filter is often demonstrated in a Physics class through a variety of demonstrations. Filters are used to look through and view objects. The filter does not distort the shape or dimensions of the object; it merely serves to produce a dimmer image of the object since one-half of the light is blocked as it passed through the filter. A pair of filters is often placed back to back in order to view objects looking through two filters. Unpolarized light can also undergo polarization by reflection off of nonmetallic surfaces. The extent to which polarization occurs is dependent upon the angle at which the light approaches the surface and upon the material that the surface is made of. Metallic surfaces reflect light with a variety of vibrational directions; such reflected light is unpolarized. Polarization can also occur by the refraction of light. Refraction occurs when a beam of light passes from one material into another material. At the surface of the two materials, the path of the beam changes its direction. The refracted beam acquires some degree of polarization.

Polarization of light is very useful in many aspects of optical microscopy. The microscope configuration uses crossed polarizers where the first polarizer is placed below the sample in the light path and the second polarizer is placed above the sample. The concept of using two polarizers oriented at right angles with respect to each other is commonly termed crossed polarization and is fundamental to the practice of polarized light microscopy.