Appliance Design - November 2007 - (Page 19)

DISPLAYS & INDICATORS Manufacturers of cellphones and other portable devices are turning toward LED technology. Photo: Avago Technologies. the limitations of the materials used to build the LED. Today, the semiconductor dies that are the heart of what gets made into an LED have improved to the point where luminous intensity is in the thousands of millicandelas. A candela is the measure of how much light is produced at the light source. Today’s red LEDs can go higher than 12,000 mcd, green can go up to 22,000 mcd, and blue to more than 5,000 mcd. One of the things that designers should be aware of is that there can be variations in brightness levels from LED to LED, says Jeff Oliveros, director of engineering for Lumex, Palatine, Ill. Variations can also occur in color as well, which is important as color LEDs continue to enter the marketplace, he says. A human’s eye has different sensitivities to color. For instance, a human eye is not as sensitive to red as it is to other colors. If one red LED is 25 percent brighter than its neighbor, most consumers cannot tell the difference. But, with colors such as green and yellow, a 10 percent difference may be noticed. Suppliers are aware of this and many have introduced into their production processes a binning process in which like items are sorted into bins. Oliveros says that his company bins for both wavelength, which is the color, and also intensity. “Binning is critical if you have an array of LEDs because you don’t want one side looking duller than another, or one side brighter than the other side,” he says. Beyond brightness, a broader color palette has been one of the biggest developments in LED technology. Just about every color in the rainbow can be achieved through one of two methods — by using a phosphor, or by www.applianceDESIGN.com combining red, green and blue LED materials onto a single semiconductor chip. The less expensive method is adding the phosphor, a tried-and-true technique that allows for a range of colors to be attained at a relatively inexpensive cost. “We have new colors coming out all the time because of the industry’s capability of phosphoring the chip in different ways to make any shade of color the designer wants,” says Saffa. By phosphor coating the lens, different colors and shades are developed. For instance, a white LED might be available in cool white, pale white and incandescent white. The cool white would have the least amount of phosphorous and would be brighter. The incandescent white would have the most and would be the dimmest, while the pale white would be somewhere between the two extremes. More expensive is placing the different color RGB chips into a single discrete package. Its strength is in the millions of possible colors it can generate by varying the individual color’s intensity levels, says Saffa. For some applications a fourth die or chip of an amber or yellow color wavelength is added to give even more options and enhance color rendering. While this technique is more expensive, costs are expected to drop across the board as it has for blue LEDs. For years, blue had been expensive to make, and purchase, and its intensity was not as good as other colors. Today, newer fabrication technologies and materials including the use of indium gallium nitride (InGaN) materials have lowered the cost of blue LEDs. According to Man Yu, engineering manFor more Information Enter 107 applianceDESIGN AD11074King.indd 1 November 2007 19 10/12/07 9:45:10 AM http://www.us.kingbright.com http://www.us.kingbright.com http://www.appliancedesign.com

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Appliance Design - November 2007 Contents Editorial Shipments/Forecasts News Watch Today’s LEDs are Brighter and More Colorful than Previous Versions, Allowing Designers More Opportunities to Improve and Differentiate Their Products. When Converting from CCFL to LED Backlights in LCD Panels, New Driving Methods are Needed. Electrowetting Technology Allows Displays to be Designed in an Extensive Range of Colors. Noise Problems are Not Always Easy to Find or Fix, but Acoustic Labs Can Help Designers Ferret Out the “Good” Noise from the “Bad.” A New Sanitization Protocol for Clothes Washers Combines the Best of Three Well-Established Provisions to Ensure Efficiency, Quality and Safety. Stricter EMC Requirements Raise the Bar for Appliances with Electronic Controls and Require Testing to New Levels. Despite Added Cost and Complexity, Gas-Modulating Systems have Migrated from Large-Scale Boiler Applications to Smaller Residential and Commercial Furnaces and Appliances. A New Treatment Technology Hardens the Surface of Light Alloys such as Aluminum and Magnesium and Expands Their Potential Applications. DesignMart Advertiser’s Index Association Report: AHAM

Appliance Design - November 2007

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