SPIE Professional August 2011
By Alan Tirpak and Alexandre Y. Fong
The intrinsic versatility of LEDs as illumination sources, coupled with a world-wide push for energy-efficient lighting, has driven the double-digit growth of the LED and solid-state lighting (SSL) industry even through the recent recessionary economic periods. As demand increases and competitive offerings proliferate, so does the need to better define performance specifications.
Several initiatives are under way to standardize the measurement methodology to address this need. There are several major methodologies involved in assessing these photonic devices and more than a few standards organizations and governing bodies contributing to this effort.
Growth of green lighting
LEDs and solid state lighting have come a long way from the single T 1-¾ devices once found ubiquitously as status indicators on consumer electronics. The Information Network recently predicted that the LED chip market was expected to increase more than 40% in 2011. Strategies Unlimited reported in its annual review and forecast in August that the overall LED industry grew in 2010 more than 90% from 2009.
Moreover, specific applications areas, such as display backlighting and signage, are expected to grow as much as 40% worldwide through 2013, according to a June 2011 report from IMS Research. However, areas such as general illumination, automobile, and other vehicle lighting remain in the early stages.
Governments around the world are investing in developing the next generation of these devices. The U.S. Department of Energy (DOE), for example, allocated $14.8 million to LED lighting research earlier this year.
The promise of improved performance and efficiency, together with the economic scale of the opportunity, has meant that objective and effective product metrics have become an area of critical interest for the supply chain and those charged with the development of the industry.
The instruments used in the testing of LED parameters are also playing a role in this prospering industry. See related articles on pages XX and YY.
The International Organization for Standardization (ISO), the International Electrotechnical Commission (IEC), and the National Electrical Manufacturers Association (NEMA) are among several organizations throughout the world developing standards for the LED lighting industry. The DOE also has several standards' initiatives, including the Commercially Available LED Product Evaluation and Reporting (CALiPER) program.
Such efforts seek to either adapt accepted techniques and standards to these new devices or develop new methodologies to better address the properties of solid-state lighting and provide a more reliable and accurate assessment. With the rapid, almost daily introduction of new technologies in this field, most efforts are still in the formative level.
LEDs and other forms of solid-state lighting are typically assessed in terms of color, efficiency, and emitted energy and brightness. In the lighting industry, output is expressed in photopic units that correspond to the eye's daylight response. Elsewhere, radiometric units that indicate output in terms of energy are used. See R. Young, et al, "Reducing Uncertainty in Precision High Brightness LED Measurements," Photonics Spectra (December 2005).
Early on in the development of optical measurement techniques for LEDs, the International Commission on Illumination (CIE) developed a technical recommendation document (CIE 127:2007) that defined the quantities and methods and which has become the foundation for all of solid-state lighting, including arrayed and composite devices such as luminaires or light engines. This CIE 127 document has been adopted by other bodies such as ISO for their documents.
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