Vibrant reflections: Red, yellow, and magenta test swatches made from novel luminescent materials are shown next to an array of color standards used to evaluate the quality of displays. Researchers at HP are using these materials to develop more vibrant reflective displays.
HP

Computing

Brighter Color for Reflective E-Reading Displays

HP is developing new materials for brighter low-power displays.

  • Thursday, July 15, 2010
  • By Katherine Bourzac

Electronic paper that reflects light, instead of filtering it from a backlight, as most conventional displays do, is easy on the eyes and saves on battery life. But this reliance on ambient light becomes a handicap when trying to make a bright, beautiful color display. Researchers at HP are addressing the problem by developing new materials that use ambient light to create a more vibrant color for video-capable, low-power screens.

Conventional displays, including LCDs, use a backlight to produce light, and layers of optics to filter it to create different colors. This type of display needs a lot of power because most of the light is lost during filtering.

Reflective displays need no backlight. For example, the pixels in the displays made by E Ink, the dominant electronic-paper company, are filled with black and white capsules of opposite charges; when the pixels are switched, the white or black particles move to the surface, reflecting or absorbing ambient light.

Making color electronic paper is a major challenge, and the prototypes made so far look muddy and dim compared to conventional displays. Adding color filters over black-and-white pixel arrays--the approach taken by E Ink--introduces the same light-loss problems that LCDs suffer from. But in an LCD, the backlight can be pumped up to maintain brightness. Reflective displays are limited to ambient light, and that loss can't be recovered. Another problem is that the colored subpixels used in color displays typically sit side by side, with one-third of the area of each pixel given over to each color: red, blue, and green. When the pixel is reflecting red light, two-thirds of the incident light is simply lost, no matter how good the filter is.

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Gary Gibson, a scientist in the information surfaces lab at the company's Palo Alto, CA, is involved with a project aimed at addressing the dimness problem using brighter, luminescent materials. The company has developed a composite material that converts blue and green light into red and another that converts blue light into green. It isn't practical to make a blue luminescent pixel. A fast-switching liquid-crystal shutter sits above each pixel and lets light in and out; mirrors below also help light escape.

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190 Comments

  • 571 Days Ago
  • 07/15/2010

color e-ink

It seems to me that the "right" way to do color e-ink, analogous to how color ink on paper works, is to create three layers of pixels that switch between transparent and absorbing R G B ranges respectively. These are the equivalent of cyan magenta and yellow inks. The substrate of this display could be something like black and white E-ink, allowing for deeper and sharper blacks (just as black ink is used on paper). Note that color resolution can be much lower than B&W.
Of course, how to do this, and do it inexpensively, is the issue.

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simplycast

5 Comments

  • 510 Days Ago
  • 09/14/2010

Interesting

I can be sure that probably in the next 39 years this will be total way of reading books

I like the old fashion way

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