Outdoors, Polarized Sunglasses, and a Blacked-Out LCD

DisplayMate president Raymond Soneira emailed me about an interesting topic. Got polarized sunglasses? Your iPad’s beautiful LCD will look black. Soneira:

All LCDs and some OLEDs have issues with polarized sunglasses – smartphones, tablets, e-readers, laptops, computer monitors, and even HDTVs. More and more people have them and they can significantly interfere with the seeing the display – the screen can become invisible. Of course all of this should only matter outdoors, although movie stars and other people also wear sunglasses indoors, so be careful.

With polarized sunglasses all iPads go black in portrait mode. Other LCD displays go black in landscape mode. Much better is for the manufacturer to set the extinction at 45 degrees so the display looks good in both portrait and landscape modes. The Motorola Xoom behaves this way as do many smartphones, laptops and even computer monitors. Best of all, with compensating films this effect can be made to go away almost entirely by converting to circular polarization. The iPhone 4 and Samsung Galaxy Tab 10.1 do that and have no extinction at any angle (just a small color shift). This extinction effect should only apply to LCDs because they use polarized light internally. LCD TVs, not surprisingly, have their extinction set for portrait mode, so you will only notice it if you are watching TV lying down with polarized sunglasses.

I took out my decade-old, but still like-new Nike progressive sunglasses and took a look at my iPad. The LCD doesn’t go completely black in portrait mode, but it gets dark enough to make it almost impossible to work with let alone read an ebook on. Brightness recuperated as I slowly rotated the iPad to landscape mode.

I wonder why the display engineers at Apple didn’t apply a circular polarizer on the iPad like they did on the iPhone. Did they think we would never don polarized sunglasses and use the iPad in portrait mode? I’m a bit disappointed.

eReaders are primarily used in portrait mode, so they should not extinguish in portrait, but, for example, both the Kindle Fire and Nook Tablet do. Since both are IPS displays they should switch to landscape extinction or add circular polarization.

I wouldn’t categorize the Kindle Fire or the Nook Tablet as e-readers; they’re more like the iPad. Nonetheless Amazon and Barnes & Noble should also have applied a circular polarizer.

OLEDs should not show any extinction effect because they don’t use polarized light like LCDs. The Nokia Lumia 900 behaves this way, which is very nice, but the Samsung Galaxy S has a surprising 45 degree extinction – this effect is due to using an external linear polarizer in a quarter wave plate to reduce the screen reflectance.

Samsung stopped midway. Nokia also uses a linear polarizer but adds an extra circular polarizer retardation layer to reduce refections.

Some additional technical details – IPS LCDs can only be set for either landscape or portrait extinction. All other LCD technologies can have any extinction angle desired, of which 45 degrees is the best for mobile displays. The best solution of all is a compensating film (technically a quarter wave plate) that turns the linearly polarized light from the LCD into circularly polarized light. That is what the iPhone 4 and Samsung Galaxy Tab 10.1 have to eliminate the effect.

Circular polarizers everyone.