The E Ink Carta reflective electrophoretic display (EPD) is
a near-perfect device for reading black text on a white background. But there are applications, such as many
kinds of signage, that demand vibrant color.
Until now, the only way to get "full" color from an EPD -- at
least the only way that E Ink has shown us -- is placing a matrix color filter
in front of the monochrome display.
E Ink's full-color
electrophoretic display with four colors of particle and no matrix color
filter. (Photo: Ken Werner)
The problem with this approach for a reflective display is
that the 40% of light reflected from a good EPD is brought down to 10-15% by
the filter. This results in a limited gamut of rather dark, muddy colors. E Ink showed the way forward a few years ago
with a black, white, and red display, which managed to control particles of
three different colors using differences in mobility and a cleverly designed
controlling waveform.
At Display Week 2016, E Ink introduced an impressive
expansion of this approach, in which particles of four different colors are
included within each microcapsule, given different mobilities through different
sizing, and driven with a pulsed controlling wave movement that permits the
creation of thousands of colors, as explained by E Ink's Giovanni Mancini.
How the E Ink display
makes 8 essential colors. (Graphic: E Ink; Photo: Ken Werner)
The resulting display showed impressively bright and
saturated colors and drew crowds. When a
new image was written, the display would flash several times. It took about 10 seconds for a new image to
build to its final colors. One possible
application Mancini mentioned is a color E Ink sign powered by photocells.
This is a significant development that will definitely
expand the range of applications EPD can address. – Ken Werner
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