Linearly polarized light passes through the quarter wave retarder. The quarter wave retards the velocity of one of the polarization components (x or y) one quarter of a wave out of phase from the other polarization component. At this point, the light becomes circularly polarized. One sometimes refers to the action of the quarter wave as “twisting” the polarized light. Note that depending on which polarization component is retarded, one will have either a left handed or right handed circular polarizer.
If a quarter wave retarder is added to the polarizing filter, the polarized light from the display is taken a quarter wave out of phase. This is essentially "spinning" the exiting polarized light from the display where it cannot work against the added polarizer. This combination of a linear polarizer and quarter wave retarder creates a "circular" polarizer. Now, the glare and reflecting performance of the polarizer can function without conflicting with the forward display polarizer. A circular polarizer can now cut reflection and glare without blanking out the image on the display. Luminary Optics has stock linear polarizing films as well as sheet quarter wave retarder. We custom match the correct angle of the polarizer to the front polarizer of the display. Then, we set the quarter wave retarder to the polarizer, creating the perfect circular polarizer. The most common configuration for our CP filters is placing the film inside of two pieces of AR glass. This combination will index match all surfaces, absorbing all transient reflection while allowing the maximum light transmission from the display.
Linear polarizers allow light from one angle to pass completely while absorbing all light that is at a 90 degree opposition to it. All of the other angles in between will be absorbed somewhere between 1% to 99%. In the end, a linear polarizer will absorb 50% of the ambient light and reduce unwanted glare or reflection. A simple pair of polarized sunglasses are linear polarizers and work in this manner. If two linear polarizers are placed in front of the other, unless they are at the identical angle, the two polarizers will start to further block light. At 90 degree opposition, two linear polarizers will absorb 100% of the light. For this reason, a linear polarizing filter cannot be used in front of a LCD for reflection reduction. The front polarizer of the display will work with an added polarizer to cancel out any light transmission.