plane-polarized light (PPL) As light travels, it normally vibrates in all directions at right angles to the line of transmission. If a strongly absorbing crystal, e.g. polaroid or tourmaline, is placed in the light path, the rays are strongly absorbed in all directions except one, and the rays of light that emerge are confined to this one plane of vibration; i.e. the light is ‘plane polarized’. Polarization may also result from double refraction (see NICOL PRISM) or reflection.

polarized light Light waves that have electromagnetic vibrations in only one direction. (Ordinary light vibrates in all directions perpendicular to the direction of propagation.) Scientists distinguish between three types: plane-polarized, circularly polarized, and elliptical-polarized light – each depending on the net direction of the vibrations. Polarizing sunglasses use a Polaroid material to reduce the glare from light polarized by reflection from horizontal surfaces.