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How E Ink Makes E-Reading a Pleasurable Experience

by Terrence O'Brien on August 9, 2010 at 12:30 PM

What is E Ink?

"E Ink," although often used to refer to any low-power, high-contrast display like that found on e-readers, is actually a specific brand of displays. The question you should be asking is: "What is e-paper?"

Alright then, what is e-paper? Jerk.

E-paper is a type of display designed to mimic the appearance of ink on paper. While there are exceptions to these rules, most e-paper displays are black and white, lack a backlight and require electricity only to update the image on the display. This makes e-paper ideal for low-power gadgets, and situations where neither color nor full motion (like in videos) are necessary.


So how does e-paper work?

Well, E Ink and its competitors all employ some variation on the basic premise of using negative and positive magnetic charges to either display a color (usually black), or leave a portion of the display black. E Ink screens are the most popular, being found in the Kindle, the Nook and e-readers from Sony, so we'll focus on those. E Ink displays contain millions of tiny capsules, each about the width of a human hair follicle. Inside each capsule is a collection of negatively charged black particles and positively charged white particles suspended in a clear fluid. When a negative charge is applied to a capsule through the electrode underneath it, the black particles are pushed to the top and the white particles are drawn to the bottom -- in essence turning on the pixel. Once the pixel is set, no more electricity is required to keep the particles in that position. This is much slower than a traditional LCD display, but also requires significantly less power. Other versions might use tiny balls with one side "painted" black, or charged liquid dyes suspended in water or oil.

So why does e-paper perform so much better in sunlight than other displays?

Since there is no backlight on an e-paper display, a reflective surface is used beneath the pixels. This not only saves power that would otherwise be needed to pump out photons, but, since it reflects ambient light rather than compete with it, the screen can be viewed in direct sunlight without appearing to fade. The downside is that an e-paper display is hard to read in low-light situations (and impossible to read in the dark).

What makes it "better" than an LCD?

We wouldn't say it's "better" necessarily, but it's certainly better for long reading sessions -- especially if you want to read outside or on your morning commute. Since an e-paper display doesn't refresh like an LCD (which actually flashes an image, usually 60 times a second), and since it doesn't bombard your retinas with its own light, it puts less strain on your eyes, at least when the lighting is good. As an added bonus, the same thing that makes e-paper better for your eyes makes it extremely low power, allowing e-readers to go weeks without being recharged. iPads, on the other hand, generally have to be plugged in every night.

E-paper is still a technology very much in its infancy. Newer versions are able to refresh quickly enough to display video and/or full-color images, but these abilities do come at the cost of battery life. Still, even they are nowhere near as draining as LCDs, and maintain visibility in sunlight. Expect to see these displays' descendants find their way into tablets, cell phones and even laptops in the near future. Hopefully, someday soon, reading the New York Times while relaxing in the park won't result in ink-covered thumbs.

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