Signs of the Times - October 2012 - (Page 36)

LED UPDATE By Dr. M. Nisa Khan As president of LED Lighting Technologies, Dr. Nisa Khan educates the lighting industry and consumers about LED lighting. She has a bachelor’s degree in physics and mathematics, and master’s and Ph.D. degrees in electrical engineering. Email her at nisa.khan@iem-asset.com Driving LED Technology Improvements LED replacement lamps for wide-area illumination need to improve. Dr. Nick Holonyak, a John Bardeen Endowed Chair in Electrical and Computer Engineering and Physics, and professor of electrical and computer engineering at the University of Illinois at Urbana-Champaign, demonstrated the first visible LED in 1962. Soon after, he envisioned the innovative lights could eventually illuminate environments as other lamps do. Holonyak, now tagged as the father of LEDs, holds 41 patents and has received awards from three presidents – George Bush Sr. and Jr. and Russia’s Vladimir Putin. The Emperor of Japan has also recognized him. their task doesn’t include illuminating other objects. In contrast, lamps and luminaires illuminate other objects – and people – so it’s best when all lit objects appear natural, as they would in daylight. Three major aspects contribute to lighting quality, and they’re all naturally and perfectly embedded in daytime light: color, distribution and brightness. Color Because many color scientists have produced invaluable work over the past century, most lightsource color properties are recognized, appreciated and defined. Several parameters define color characterization: the color-rendering index (CRI), correlated-color temperature (CCT), color coordinates and spectral-power distribution. To clarify: • CRI provides an overall merit figure that indicates typical colorfidelity preservation when viewers perceive it under certain lighting conditions; • CCT describes the lightsource hue; • Color coordinates give the lightsource color as it relates to other colors defined by the CIE color map; • Spectral distribution provides the amount of various spectral content present in a lightsource. Measuring these quantities is reasonably straightforward, quick and inexpensive and, currently, CRI and CCT ratings exist for most retail-accessible lamps. High-quality light must have high CRI and CCT ratings in the range of 2,700K to 5,000K, depending on the application. Generally, warmer CCT (lower value) is preferred for a relaxed atmosphere, and cooler CCT (higher value) for office and working environments. Distribution Unlike color properties, spatiallumen distribution characteristics aren’t easily recognized by most people, although artists, photographers and filmmakers are knowledgeable on how light distribution in space improves illumination. Its quantification, better known as goniophotometric characterization, is laborious and expensive, and most lighting designers don’t perform such measurements. When necessary, they use known data from existing lamp catalogs. For the most part, incandescent and fluorescent lamp designs are optimized, and the available catalog data for light distribution suffices for most lighting designs. Oppositely, LED lamp technology is relatively new, and numerous lamp and luminaire designs lack standard configurations. Further, LED lamps’ light distribution is significantly different from incumbent lamps – thus, goniophotometric measurements are crucial for LEDlamp designs. Brightness Brightness is often misunderstood. Overt brightness is not always better for general or sign illumination and shouldn’t be considered a merit unless specified. Brightness, or more technically “luminance,” measured in nits (cd/m2), is an inherent property of a light source. For general illumination, source brightness isn’t rated – and almost never characterized – by lighting designers. They usually measure illuminance (in lumen/m2 or some equivalent), which can be freely described as flat-surface light density. In contrast, signage and display industries use luminance more often, and illuminance less often. The quantities are interdependent. Unfortunately, LED lighting pro- In 1962, Dr. the first visible LED Nick Holonyak demonstrated light and later became its recognized parent. Fabricated from inorganicsemiconductor alloys (which remain the preferred material system today), the new, solid-state, LED light was immediately recognized by Dr. Holonyak for its potential. Today, LEDs’ lighting-industry successes, plus its enormous role in signage and display systems, certainly excites its inventors and developers. However, the solid-state lighting (SSL) industry is now entering a phase where participants must recognize and appreciate lighting quality and determine if LED lamps and luminaires can provide superior illumination for general applications, with greater energy efficiency. Obviously, success depends upon the system’s costs, compared to incumbent counterparts for businesses and consumers, Lighting quality Judging lighting quality requires time and experience. Interestingly, it’s easier to judge the illumination quality of displays and signs, partly because we view them directly, and 36 SIGNS OF THE TIMES / OCTOBER 2012 / www.signweb.com http://www.signweb.com

Table of Contents for the Digital Edition of Signs of the Times - October 2012

Sign of theTimes - October 2012
ST Update
Technology Update
Vinyl Apps
Strictly Electric
LED Update
Software Update
Technology Review
Technology Review
Sign Museum News
New Products
2012 Vehicle Graphics Contest
Entry-level Electronic Digital Signage
The Proposed ISA Reorganization Plan
Enter ST's 2013 Intl. Sign Contest
SGIA Expo 2012
The Value of Signs
Advertising Index
Editorially Speaking

Signs of the Times - October 2012