Signs of the Times - April 2013 - (Page 28)

LED UPDATE By Dr. M. Nisa Khan As president of IEM LED Lighting Technologies, Dr. M. Nisa Khan consults in the solid-state lighting industry and educates 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 Understanding LED Illumination My forthcoming book addresses science, art and the human psychology of LEDs and lighting. Over thethe world by offering visibility have enormously past 100 years, electric lights changed during darkened hours. Electric lamps have brought benefits to personal lives and every aspect of society – education, manufacturing, entertainment, government and all other professions. They have also illuminated signs and boosted sales for businesses. Unfortunately, artificial lighting still has not reached many parts of the world because a standard, electricpower source and distribution grid system is too costly to build in many impoverished countries. However, LED lamps are attracting attention as alternatives because they’re a practical, low-power, electric-light system that doesn’t require a grid. LED lamp technologies that incorporate smart controls promise to revolutionize the lighting industry by lowering energy consumption. Such systems will also feature increased lifespan and improved reliability compared to incandescent and fluorescent lamps. The world could save a great deal of energy by switching to LED lighting, because the systems are more efficient and can run both on and off an electric grid. To reach this goal, the LED and the traditional lighting industries must close their long-standing gap. So, what actually is this gap and how can relevant industry participants close it? The more I learned about lighting, the more the gap became readily apparent. I came into the lighting industry from the optoelectronics industry, which actually spawned LEDs decades ago. Previously, I had worked as a physicist and electrical engineer, having concentrated on optical science and semiconductors. Like many professionals in the optoelectronics community, I innovated new optical technologies and products. Although the optics field requires intricate work, few, if any, of us, really understood or appreciated lighting. This note has been echoed by many lighting authorities, including Dr. David DiLaura who, at Lightfair 2009, said, “…LED people don’t know lighting from licorice, but that they will learn.” He was right on both counts. Lighting is an optical science. It deals with electromagnetic radiation within the visible spectrum. It’s also art, and relevant to human psychology. Note, also, that lighting, meaning the illumination of an area, deals with light perceived by the human eye, which is different from light captured by photodetector devices. The distinction is complicated, but important to recognize. Physical lighting quantities are only perceptions of the human eye, and these perceptions aren’t truly analogous to other physical quantities. 28 SIGNS OF THE TIMES / APRIL 2013 / For example, optical power detected by a fabricated sensor is radiant optical power measured in watts, but we don’t “see” watts. What we see is luminous flux, which we quantify with a parameter called “lumen”. It all leads to the distinction between efficiency (the degree to which something is done well) and efficacy (the ability to produce the desired result). Lighting scientists express the merit quantity “lumen/watt” as efficacy (use “efficiency” when both quantities before and after conversion can be expressed by the same unit). Luminous flux is generated from radiant power emitted by a lightsource, and it usually scales with the source power – but not always and not always the same way. Radiant power converts to what we perceive by weighting it with the human-eye sensitivity function at each wavelength in the visible spectrum and then summarizing them. However, applying such a conversion method doesn’t always lead to what we see in different environmental conditions, because our perception is also affected by light levels, contrast, color and other physical parameters, as well as subjective parameters and each person’s vision adaptability. Nevertheless, such conversion methods remain the best approaches we have to quantify lighting. Most fascinating is the aspect of lighting that’s beyond traditional optics and other hard sciences and engineering. As one explores this facet, two things become clear: a) Lighting is a field in its own right, and many lighting, vision and color scientists have served the field as notable contributors. b) LED lighting, because of the intricacies of optoelectronic science and manufacturing technologies, is more complicated than most LED and lighting scientists and engineers realize. LEDs are a different kind of light source, and understanding them requires knowledge of the fundamentals of lighting sciences and mathematics. My forthcoming book, “Understanding LED Illumination,” will be released in August. Its seven chapters offer the following features and benefits: 1) The basic notion of emphasizing the lighting aspects of LED lamps. The solid-state lighting (SSL) community should recognize that LED lamps must provide more than a glow and higher luminous efficacy. The quality of the glow must also be improved and be effective. 2) The basics of junction diode, and the intricacies of compound-semiconductor optoelectronic properties, including thermal, electrical, optical and mechanical aspects. The book provides lighting-industry professionals with a compact source from which to

Table of Contents for the Digital Edition of Signs of the Times - April 2013

Signs of the Times - April 2013
ST Update
Cut Your Ink Costs
Technology Update
Vinyl Apps
Strictly Electric
LED Update
Software Update
Technology Review
Technology Review
Sign Museum News
New Products
The 2013 International Sign Contest
Leasing Equipment
The ISA Sign Expo 2013 Preview
Industry News
Advertising Index
Editorially Speaking

Signs of the Times - April 2013