Appliance Design - May 2008 - (Page 22)

DISPLAYS & INDICATORS bottom, rendering the cell into its light state. When the trailing edge of the electrical pulse is smooth, the liquid crystals will realign into a uniform state that blocks reflected light and places the cell into a dark state. The liquid crystal materials re-anchor after the pulse and, therefore, maintain their new configuration until another pulse is applied. Each company’s product’s has the ability to work in grayscale and monocolor. Traditionally, e-paper has not used color because color can affect brightness levels, which affects readability. To achieve color, there are two primary methods. Nemoptic uses a combination of color filters with gray levels. For SiPix, the colors are created from the dies that are in the Microcup. For its part, E Ink is working with color products in the labs and is doing testing on the product to ensure optimum readability. To date, it has demonstrated full color displays using a RGBW color filter array over high contrast black and white ink. Because readability is a vital consideration, factors such as contrast and reflectance are critical. On first blush, when looking at the contrast ratios, the numbers would look very small compared to a system that displays video or compared to an LCD monitor, but reflective displays are measured differently. According to Chan, the contrast ratio is defined as the ratio of how “white” is white compared to how “black” is black. Electrophoretic systems have a contrast ratio that ranges between 6:1 up to 20:1 depending on the system. By comparison, newspaper has a contrast ratio of about 4:1 or 5:1, while a typical, digital wristwatch has a contrast ratio of about 3:1. Chan adds that the differences are not as important as they may appear, as there are limits to the contrast ratio that humans can detect. He says with a reflective display it is difficult to distinguish any ratio above 10:1 unless they are side by side. (A higher contrast ratio is better than a lower contrast ratio.) Reflectance is another important issue. While contrast ratio compares black and white, reflectance determines how much light is reflected back from the display. Nemoptic’s new A4 e-paper display is 210 mm x 297mm and has a resolution of 200 dpi. Shining a light onto a surface and capturing the amount of light that bounces back determines reflectance. A very white sheet of paper can be anywhere from 80-95 percent. E-paper comes nowhere near that figure, but it doesn’t have to. Typically, reflectance above 30 percent is not noticeable unless they are compared side by side. Reflectance is also pivotal when it comes to the viewing angle. E-paper’s reflectiveness is different than a mirror where the light bounces back at Motorola Motophone with ClearVision display based on E Ink technology. A point-of-purchase display with area color developed by SiPix Imaging. 22 applianceDESIGN May 2008 www.applianceDESIGN.com http://www.appliancedesign.com

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Appliance Design - May 2008 Contents Editorial Shipments/Forecasts News Watch New and Notable Displays & Indicators Elastomers Quality & Standards Indoor Air Quality IHHS Highlights New Products Classifieds Design Marts Advertiser’s Index Association Report: PSMA

Appliance Design - May 2008

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