Polarized Glasses and Electronic Displays: A Brief Tutorial

For those sensitive to light few accessories are more valuable than polarized sunglasses. Polarized lenses work by filtering out photons (light) oscillating horizontally. While natural light from the sun oscillates in all orientations, light from most electronic displays will all share a single orientation.  But why is that?

Many modern displays rely on polarization

In most common displays light starts it’s journey by being emitted from an LED behind the display, also known as a backlight.  At this point the photons oscillate in all directions, much like they do if they are emitted from the sun.  However, the photons then pass through a polarizing layer at the back of the display.  That polarizing layer alters oscillation of the photons to a single unified orientation.

What happens next depends on whether the pixel (millions of these ‘dots’ make up the image displayed) is open and displaying light, or whether it’s closed and displaying black.

If the pixel is open, then the photons passing through the pixel are twisted in the liquid crystal layer to allow them to pass through the later polarized filter layer that is perpendicular to the polarizing layer.  This allows those photons to exit out the front of display and reach your eyes, appearing as light.  The proportion of photons twisted depends on how bright the pixel is supposed to be.  A bright white pixel will mean most or all of the photons have been twisted to allow them through and to reach your eyes.  A grey pixel might twist only half the photons through, resulting in a pixel that is less bright.

If the pixel is closed (eg. the pixel is black) then the photons are not twisted and they then become blocked by the polarized filter layer.  As the photons are blocked by that layer they will not reach your eyes and thus appear black.

Twisted nematic field effect ‘twists’ the oscillation of photons that are intended to be shown as light on a display, so that they are not blocked by a polarized filter before exiting the display.

The above description is what’s known as the twisted nematic field effect.  The technology has been around for several decades but most recently has been adapted to for use in conjunction with more modern, advanced displays.  It is, however, not present in organic LED displays (“OLED” or “AMOLED”) as the pixels in those technologies actually emit light themselves rather than relying on a light present behind the display.

The problem with polarized glasses

If the display’s polarizing layer converts photons to a vertical oscillation, and the twisting layer then converts them to a horizontal oscillation so they can pass through the polarized filter, then all the photons from the display will be horizontal.  Since your polarized lenses block photons oscillating horizontally, the light will ultimately be blocked in whole or in part by your polarized sunglasses, rendering the display impossible to use.

On the other hand, if the polarizing layer starts the photons out as horizontal and the twisting layer converts them to vertical, then a vast majority of the photons emitted from the display will pass through your your polarized glasses and ultimately reach your eyes, appearing as light.

Some displays emit photons that oscillate vertically, some as horizontal, and many somewhere in between at a 45 degree angle.  Unfortunately there is no standard photon orientation for displays so until you check them against polarized lenses you won’t know if they are compatible or not.

Our measurements on TechSensitive.com are performed using reference Maui Jim ‘276 Manu 65’ sunglasses equipped with brown/bronze polarized lens.

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