How does E Ink® work?
by Chris Woodford. Last updated: November 20, 2013.
The world's great libraries are stunning stores of knowledge, but
sometimes they might as well be in space, because much
of the information they contain is so far beyond our reach. There's
no easy way to search through billions of pages of old and dusty
paper—and the problem gets worse every year as millions more books
are added to the pile. Fortunately, the development of computers from
the mid-20th century led to better ways of storing information so
that it could be indexed, searched, and retrieved more quickly, while
the invention of the World Wide Web meant anyone could access
computerized knowledge from anywhere. In the last few years, paper books have
started to be replaced by ebooks such as the Amazon Kindle™
and Sony Reader. Portable devices that can hold books are nothing
new: they've been around since Sony launched its original attempt, the
Data Discman, in 1990.
What made them finally take off was the development of light and
legible displays using electronic ink and paper. How
exactly do they work? Let's take a closer look!
Photo: Ebook readers (like this Sony Reader and the Amazon Kindle) use electronic ink displays made by E Ink Corporation. They're lightweight, consume very little power, and are easy to read even in bright sunlight.
What is electronic ink?
You're probably reading these words in the same way that I am—by staring at
a flat, LCD computer screen. For people over the age of about 35, who
grew up with computers that used blocky green and black screens with
just 40 characters across and 25 down, modern screens are wonderful
and amazing. But they still have their drawbacks. Look closely, and
you can see jagged edges to the letters. Try to read an LCD screen in
direct sunlight and (unless the screen has a very bright backlight), you'll really
struggle. But the worse thing is that LCD screens lack the
lightness, portability, and sheer user-friendliness of ink-printed paper:
you can happily read a book for hours, but try the same trick with a
computer screen and your eyes will quickly tire.
Photo: Computer screens as we knew them in the late 1970s and early 1980s. At that time, the best screens could display no more than about 64,000 pixels and often just uppercase text or very crude "pixelated" (square block) graphics. Computer games like Space Invaders, shown here, were very primitive—but still highly addictive!
Back in the early 1970s, the Xerox Corporation that had pioneered
photocopiers a decade earlier became concerned about the threat that
computers might pose to its core ink-and-paper business: if everyone
started using computers, and offices became paperless, what would
happen to a company so utterly dependent on paper technology? It was
for that reason that Xerox pumped huge amounts of money into PARC™,
(Palto Alto Research Center), the now-legendary campus where modern,
user-friendly personal computing was pioneered. Among the many innovations
developed there were personal computers that used a
graphical user interface
(the "desktop" screen featuring icons, later copied by the Apple Macintosh® and Microsoft Windows®),
laser printers... and electronic paper, which was invented
by PARC researcher Nick Sheridon.
The basic idea of electronic ink and paper was (and remains) very simple: to produce an electronic display
with all the control and convenience of a computer screen but the
readability, portability, and user-friendliness of paper.
Photo: The E Ink® display on a Sony Reader (bottom) is much sharper and easier to read than a typical LCD screen (top). Magnifying by about 8–10 times and zooming in on a single word, you can see why. The E Ink display makes sharper letters with a uniformly white background. The LCD display blurs its letters with anti-aliasing to make them less jagged, though that makes them harder to read close up. The red, blue, and green colored pixels used to make up the LCD's "white" background are also much more noticeable. Unlike the E Ink display, an
LCD does not use a true white background: it relies on your eye and brain to fuse colored pixels instead. The resolution of E Ink is also far greater: typical LCD displays use around 90 pixels per inch, whereas E Ink displays use at least twice as many pixels.
How does electronic ink and paper work?
Most electronic ink and paper screens use a technology called
electrophoresis, which sounds complex but simply means using
electricity to move tiny particles (in this case ink) through a fluid
(in this case a liquid or gel). Other uses of electrophoresis
include DNA testing, where electricity is used to separate the parts
of a DNA sample by making them move across a gel, which enables them
to be compared with other samples and identified.
In one of the best-known electronic ink products, called E Ink® and used
in ebooks such as the Amazon Kindle, there are millions of microcapsules,
roughly the same diameter as a human hair, each of
which is the equivalent of a single pixel (one of the tiny squares or
rectangles from which the picture on a computer or TV screen is built
up). Each capsule is filled with a clear fluid and contains two kinds
of tiny ink granules: white ones (which are positively charged) and black
ones (which are negatively charged). The capsules are suspended
between electrodes switched on and off by an electronic circuit, and each one
can be controlled individually. By changing the electric field
between the electrodes, it's possible to make the white or black
granules move to the top of a capsule (the part closest to the
reader's eye) so it appears like a white or black pixel. By controlling
large numbers of pixels in this way, it's possible to display text or
Animation: Electronic ink works through electrophoresis. Each pixel (microcapsule) in the display (the gray circle) contains black (negatively charged) and white (positively charged) ink granules. When a positive field (shown in blue) is applied to the top electrode, the black capsules migrate to the top, making the pixel look black when seen from above; switching the field over makes the granules change position so the pixel appears white.
Advantages and disadvantages
If you've tried reading an electronic book, you'll know that electronic ink
and paper is much easier to read from for long periods than an LCD
computer screen. Since the microcapsules stay in position
indefinitely, with little or no electric current, electronic ink
displays have extremely low power consumption. A typical ebook reader
with an E Ink display can be used for something like 2–4 weeks of
average everyday reading on a single charge. Low power consumption means
low energy use and that translates into an
environmental benefit; in
other words, electronic ink and paper is environmentally friendly.
The disadvantages are less obvious until you start using electronic ink
in earnest. First, although the displays work excellently in bright
indoor light and daylight, including direct sunlight, they have no
light of their own (unlike LCD displays, which have backlights shining through
them from back to front so you can see them). That makes them hard to use in poor indoor light,
especially in the evenings, which is why many ebook readers are sold
with clumsy addon lamps. Electronic ink also takes much
longer to build up the image of a page than an LCD screen, which means
it's unsuitable for everyday computer displays using any kind of
moving image (and completely unsuitable for fast-moving images such
as computer games and videos). Sometimes parts of a previous page
linger on as "ghosts" until you've turned another page or
two. You've probably noticed that, when you "turn the page"
of an electronic book, the entire screen momentarily flashes black
before the new page is displayed? That's a rather clumsy compromise
to prevent ghosts, in which the screen tries to erase the previous
page before displaying a new one (a bit like
Another major disadvantage is that most electronic ink displays are currently
black and white. Color displays do exist (E Ink produces one called Triton, in
which a layer of red, green, and blue color filters is mounted over
the usual black-and-white microcapsules) and better ones are in development, but they're much more expensive than their
black-and-white electronic paper (or LCD equivalents). In time, we're
bound to have color electronic books and magazines; according to
Amazon's Jeff Bezos, however, speaking in mid-2009, a color Kindle ebook
reader is "multiple years" away: "I've seen the color displays in the laboratory and I can assure you they're not ready for prime time." (Amazon's color Kindle Fire™ product, announced in September 2011, uses an LCD display.)
Photo: Night and day, are you the one? Here I've propped a Sony Reader against the screen of a conventional laptop and photographed it in different light conditions. Left: In bright light or daytime outdoors, electronic ink displays are much easier to read than backlit LCD displays, which become virtually invisible. Right: In dark indoor light in the evenings, things are reversed: LCDs are much easier to read and electronic ink displays are a struggle to decipher unless you sit in strong light (or use a clip-on light attachment).
What is electronic ink used for?
Electronic books are still by far the biggest application, but there are as many
potential uses for electronic paper and ink as for their ordinary
equivalents. Billboards, point-of-sale shop displays, grocery store
labels that change their prices automatically, and street-side bus
and railroad timetables that can be updated remotely from the depot
are just a few of the likely applications we'll see in time,
especially when color technology becomes more affordable.
Find out more
On this site
On other sites
- E Ink Corporation: Lots of interesting technical information and background from the manufacturers of E Ink.
- YouTube: E Ink: E Ink's YouTube channel has some great little videos demonstrating black-and-white and color displays.