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