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Amazon Kindle Paperwhite frontlit display
A technical look at Amazon Kindle's Paperwhite display


By Rasmus Larsen (@flatpanels)
11 Sep 2012

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You have probably already seen an E-reader, or maybe you even own one most likely one of the Kindles. The new Amazon Kindle Paperwhite now has a “frontlit e-paper display” that is useable in the dark. But what is that and how does it work? FlatpanelsHD explains.

How a Frontlit E-paper display works

Before we start talking about the Kindle Paperwhite we should define what an E-paper display really is. E-paper and E-ink is often referred to as electronic paper because it mimics the appearance of ordinary paper.

We could go into many details about how it is made but right now it is just important to understand that e-paper looks like paper and has traditionally differed from typical LCD screens because it reflects light from the outside world and uses it to light up the screen whereas a LCD has a backlight unit that lights up the screen from behind.

Amazon Paperwhite
Amazon’s new Paperwhite with a frontlit display


E-paper displays have advantages such as a pleasant reading experience, extremely low power-consumption and provide users with the ability to read in sunlight. Because it is reflective it just gets brighter when you sit in a brighter environment for example outside. But e-paper displays like real paper are impossible to use in a dimly lit room or during a flight when lights are out.

Amazon Kindle Paperwhite fixes that. Now you can use your e-reader in a completely dark room


To make reading in a dark room possible, Amazon made some changes. The display in the Kindle Paperwhite now uses a layer that can distribute light from the front, thus “frontlit”. Instead of using a backlight unit like LCDs the frontlit construction ensures that the display still feels very pleasant and still looks like paper and not an actual screen. And the battery life should still be excellent, according to Amazon.

Amazon Paperwhite
Amazon uses a light guide layer to distribute light from LEDs, picture: The Verge


How it works

Amazon has not revealed exactly how (because it is patented) but broadly speaking it works by using a light guide layer that is located underneath the anti-glare layer. The LEDs (light emitting diodes) are placed at one of the edges and light is then guided out on the light guide layer and down from the top into the e-paper display with the use of a light diffuser. The light diffuser’s purpose is to distribute light evenly on the screen which is done by having tiny holes in the layer. Closest to the LED source the holes are farther away and further away from the light source the tiny holes are more concentrated. This is necessary because the LEDs are placed at one edge only.

Amazon Paperwhite
The light guide has tiny holes with different space distance


The Amazon Paperwhite display also has a higher resolution (221 ppi) and “25 %” greater contrast (whiter whites and blacker blacks), Amazon says. That should make letters on the screen even clearer and sharper. And the display now also utilizes capacitive touch that should make touch input faster and better. Previous generations of the Kindle used an infrared touch technology where infrared sensors where placed at the edge of the bezel. Infrared touch technology is far slower and more inaccurate.

So, there you have it. Now e-paper displays work in the sun, in a brightly lit room and in rooms without light. It is electronic paper version 2.0. But can it actually replace real paper now and save our rain forests?

Barnes and Noble use a similar principle in their Nook with “glowlight” and we should probably expect to so many more e-readers with frontlit displays in the future.

- Source: Amazon, picture from The Verge





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