Stakeholders make progress on LED lighting horticulture standards
Human-oriented lighting metrics don’t necessarily apply to how plants use light, explains Jianzhong Jiao, and the horticultural industry needs metrics for LED performance and efficiency relative to the application.
In recent years, LED lighting for horticulture applications, in particular plant-growth research and production in the controlled environment, has dramatically increased. The benefits of using LEDs for energy savings and performance improvement have been quickly recognized by researchers, plant growers, and greenhouse or controlled-environmental-chamber manufacturers, as well as government and energy savings experts. LED horticultural lighting is a fast-growing market, yet there are uncertainties as to how LED lighting products should be measured, compared, and qualified in regard to energy savings, performance, and safety.
Illuminating Engineering Society updates LED testing standards
Jianzhong Jiao explains the expanded scope of the new LM-80 standard with coverage of color along with white LEDs and test methods defined specifically for DC high-voltage, AC, and other variants of the simple discrete LED.
The IES LM-80 standard is a document developed by the Illuminating Engineering Society of North America Testing Procedures Committee (IES TPC). Its purpose is to provide uniform testing methods to obtain information on LED luminous flux and chromaticity changes, and allow a reliable comparison of LED characteristics when comparing products from different manufacturers with test results from different laboratories. But the LED landscape has shifted considerably with new types of component architectures, and new LED product development concepts such as tunable luminaires. The IES TPC has therefore worked to revise LM-80 to ensure it serves the intended purpose given the current state of LED technology.
ANSI works to update the solid-state lighting standard for chromaticity
Industry trends such as warmer LED-based products below 2700 K and the demand for tighter color uniformity are driving continuous improvements in the ANSI LED chromaticity standard, explains Jianzhong Jiao.
The ANSI (American National Standards Institute) organization is again working to update the LED chromaticity specification – C78.377. As LED sources have evolved and LED developers broadened the range of luminaires produced, the need has arisen to expand the standard scope while tightening some parameters to ensure better LED products for lighting specifiers and developers. Indeed, the latest revision will include coverage below the prior 2700K-CCT (correlated color temperature) floor as developers embrace warmer lighting for some specialty applications, while also making tighter color uniformity a requirement across the board.
IES establishes new standard for spectral data transfer
Jianzhong Jiao describes the intention behind and implementation of the new IES TM-27 standard for a data file format dedicated to spectral power distribution.
The implementation of LED light sources for illumination has extended the discussions about color quality, lighting for health, the biological effects of lights, horticultural lighting, and beyond. In all aspects, both LED and lighting product developers and end users are more interested than ever in the spectral content of light sources. Lighting designers have started to request more information for light source spectral power distribution (SPD) in addition to all the chromaticity related information such as chromaticity values (x,y or u’,v’), correlated color temperature (CCT), and color rendering index (CRI).
LED automotive lighting applications require unique SAE standards
Jianzhong Jiao summarizes the broad landscape of standards for LED lighting specific to automotive applications, which includes unique characteristics in terms of lumen maintenance, reliability, lifetime, and color spectrum.
The development of AlInGaP (aluminum gallium indium phosphide) materials technology in the early 1990s led to higher efficiency and better reliability in yellow-to-red light-emitting diodes (LEDs). Around the same time, LED technology for various illumination applications was on the rise. Automotive exterior lighting was one of the first such applications starting with center high-mounted stop lamps (CHMSLs). In the late 1980s, the SAE (Society of Automotive Engineers) International Lighting Committee started to develop LED automotive lighting standards and their work continues today. Most automotive exterior lighting lamps are considered safety devices, and as such, these lamps are regulated at a federal or state level. Due to the nature of safety requirements, the introduction of LEDs brought together several different perspectives that became the central focus of LED lighting standard development with the SAE Lighting Committee.
ANSI recognizes need for LED driver testing standards
Jianzhong Jiao reports on ANSI efforts that will deliver driver testing standards commensurate with the standards the LED industry has in place to test light-centric characteristics of lamps and luminaires.
The first LED lighting test standard (IES LM-79) was published in 2008 and since then, many related standard documents focused on testing have been developed or are currently in development by the IES (Illuminating Engineering Society), ANSI (American National Standards Institute), UL (Underwriters Laboratories), and NEMA (National Electrical Manufacturers Association). But the driver electronics in a LED product has been one area that lacked an accepted testing standard. Now ANSI has developed a standard for testing drivers that should allow LED product developers to more accurately compare and specify drivers, ensuring robust system-level reliability and performance.
IES updates LED Lumen Maintenance document
Jianzhong Jiao explains that the IES is publishing addendums to both the LM-80 standard for testing LEDs and documenting lumen maintenance, and to the TM-21 standard for projecting LED system life, improving and harmonizing the documents.
For continuous improvement in technology to be possible, it’s critical that corresponding testing standards are established and continue to be reviewed and improved. The LED industry is no exception. In 2008, IES published LM-80 for recommending how to test LED lumen maintenance. Three years later TM-21 was published as a recommendation for projecting long-term lumen maintenance of LEDs using the test data collected per LM-80. Based on the continuous improvement principle, IES is in the process of publishing an addendum to LM-80 and TM-21.
IES LM-85 homogenizes high-power LED measurement and characterization
The LED industry has struggled with the lack of standardized methods for characterizing LED performance, but as Jianzhong Jiao explains, the IES LM-85 standard provides comprehensive guidance as to how LED manufacturers derive specifications.
In LED applications today, LEDs that require heat sinking in normal operating conditions are categorized as high-power LEDs. As with all LEDs, the photometric characteristics of high-power LEDs — such as luminous flux, chromaticity, and temperature or current dependency — are critical pieces of information that require consistent and reliable methods of measuring and verifying by LED manufacturers and users. The IES LM-85 standard defines LED measurement and characterization methodology including accounting for realistic temperatures at which the components operate in LED products.
IES TPC considers LM standard for remote phosphor optics
Remote-phosphor technology offers potential advantages to LED such as better color uniformity and maintenance, and, as Jianzhong Jiao explains, may soon have the benefit of an IES testing standard such as the LM-80 standard defines for LEDs.
The LED industry has made great progress with standards for characterizing LED source and luminaire/lamp performance, along with standards to project lumen maintenance over time. LED-based modules that use remote-phosphor technology can be tested using the LM-80 standard defined for LEDs. But going forward, the IES is pursuing a separate LM standard that will specifically apply to remote-phosphor optics.
IES moves to establish LED light-source ray file standards
Jianzhong Jiao describes how the TM-25 IES standards effort will unify the ray file datasets used by optical CAD tools, thereby lessening the burden on LED manufacturers that are often tasked with creating the files and making optical simulation tools more broadly useful.
Computer-aided design (CAD) technology has been applied in many technology segments and is increasingly important in the optical space. Optical simulation can speed product development and ensure that new products provide optimal illumination. However, the available optical CAD software tools are largely proprietary, including the file formats used to store light-source ray files. An ongoing Illuminating Engineering Society (IES) effort is seeking to standardize ray files to ease the burden on light-source suppliers, including LED manufacturers, and make optical CAD tools more broadly applicable.
New standards will enable lumen maintenance projections for LED
Jianzhong Jiao explains that LM-84 and TM-28 will enable long-term lumen maintenance projections beyond the LED light source level, similar to how LM-80 and TM-21 are used with LEDs.
LED-based, inherently featuring long useful lifetimes, has created an issue for the lighting industry. The industry needs a way to project the useful lifetime and specifically the system-level lumen maintenance of lamps and luminaires. Standards bodies are progressing on an approach that will combine LM-84 testing data on lamps and luminaires, with a new TM-28 standard that standardizes methods on projecting the measured data over longer lifetimes. The approach parallels the way the LM-80 and TM-21 are used to project LED component lumen maintenance.
ANSI works to standardize LED datasheet for white LEDs
Jianzhong Jiao reports that the ANSI standards body hopes to facilitate the communications of pertinent component characteristics between LED manufacturers and LED product developers.
The American National Standard Institute (ANSI) is currently developing a standard datasheet for white LEDs used for general illumination, that can in turn help the LED industry overcome obstacles to broader deployment. Datasheets are an important format for LED manufacturers to present product information and characteristics to users. Over the years, more and more LED manufacturers have entered the general lighting market, and in almost all cases they use datasheets to communicate with users and assist them in selecting and implementing LEDs in lamps, light engines or luminaires. In the past, the information LEDs manufacturers have provided in these datasheets has not been consistent, and as such, users have expressed concern over lack of fair comparisons when selecting LEDs.
SEMI committee progresses in HB LED standards process
Jianzhong Jiao discusses the progress made in the SEMI organization on LED manufacturing standards, including a Wafer Task Force draft document, that should ultimately lead to more efficient and less expensive components for LED.
With the ever broadening availability of LED products for general lighting and other applications, many new standards have been, or are in the process of being developed. Primarily these standards are LED product based standards and in general they can be categorized into three areas – testing, performance, and safety. The standards can also be grouped into component level and system level (final product) standards. Standards are the measure of the industry’s maturity and are used as tools to interface between product producers and product end users. The next step for the industry is developing LED process related standards that should ultimately yield lower-cost LEDs.
Standards emerge for thermal characterization of LEDs
Jianzhong Jiao explains that accurate and standardized characterization of LED junction temperature is critical to LED product manufacturers developing optimal designs.
A light emitting diode, or LED, per the ANSI/IES RP-16 definition, is a “p-n junction semiconductor device that emits incoherent optical radiation when forward biased.” A p-n junction is formed at the boundary between a p-type and an n-type semiconductor, created in a single crystal of the semiconductor by doping or by epitaxy. Junction temperature, usually denoted as Tj, refers to the temperature at the p-n junction of a semiconductor device. Performance characteristics of LEDs, such as light output, color and lumen maintenance are a function of the junction temperature experienced by the LED during its operation. That fact means that the LED industry needs a standardized way to characterize junction temperature and other thermal specifications so that LEDs from different manufactures can be fairly compared and product designers can develop quality lamps and luminaires with appropriate thermal management systems.
JEDEC test standards and LED package reliability
LED packages that pass JEDEC tests are more reliable in real-life applications, but as yet there is no way to use the results of severe stress-testing of LED packages to project their rated life, as Jianzhong Jiao explains.
With the ongoing development of LED standards in the area of testing LEDs for reliability, the industry is referencing standards that have already been established by long-standing industry bodies such as JEDEC, the Joint Electron Device Engineering Council. For over fifty years, JEDEC has developed testing methods and product standards crucial to the electronics and semiconductor industry, which includes LEDs.
Lumen-maintenance testing for LED lamps, light engines and luminaires
Now that procedures are in place to make long-term lumen-maintenance projections for LED components, efforts are being made to develop methods for testing the lighting system as a whole, as Jianzhong Jiao explains.
It is widely understood that measuring lumen maintenance is critically important for determining the life of LED lighting products. In the past few years, the Illuminating Engineering Society of North America (IESNA) has developed two test methods that address the lumen maintenance of LED light sources used in such products. LM-80 is an approved method for measuring lumen depreciation of LED light sources, and TM-21 is a technical memorandum which specifies how to extrapolate the LM-80 data in order to make long-term lumen-maintenance projections.
Understanding the difference between LED rated life and lumen-maintenance life
The rated life of an LED light source is different from the lumen-maintenance life, and is an essential reliability value that is required by luminaire makers and end users, as Jianzhong Jiao explains.
With the completion of the IES test method TM-21-11 (see page 9), the LED industry now has a standard method of obtaining long-term lumen-maintenance information for LED light sources. The method is made up of two steps. First, the LED light sources must be tested per LM-80. The new TM-21 method is then applied to the collected measurement data to make lumen-maintenance projections, including in-situ temperature calculations.
ANSI evaluates revisions to LED chromaticity standard
A working group within ANSI is evaluating ways to improve an existing standard that defines how to communicate the chromaticity of white-light LED products to end users, explains Jianzhong Jiao.
In early 2008, the American National Standards Institute (ANSI) published its LED color standard, ANSI C78.377-2008, entitled “Specifications for the Chromaticity of Solid State Lighting Products.” For manufacturers, this standard defines how to communicate the chromaticity of white-light LED products to end users. After two years of practice using this LED standard, the industry recognized the need for improvements in its accuracy and the need to make the standard more user-friendly. In fall 2010, the ANSI Technical Committee TC78, Working Group of LED Light Source WG09, formed an ad hoc task force to define the appropriate revisions to the document, focusing primarily on making improvements without requiring major thematic changes.
LED safety standard UL 8750 requires further clarification
There is still some clarity needed in how UL 8750 addresses safety requirements for packaged LED components, which can even affect the choice of encapsulation materials, writes Jianzhong Jiao.
In November 2009, Underwriters Laboratories (UL) published a new LED light-source safety standard, UL 8750, entitled “Light Emitting Diode Equipment for Use in Lighting Products.” This standard was based on research described in the “Outline of Investigation” report that UL had spent over two years developing. The report includes input from approximately 45 members of the UL 8750 Standard Technical Panel (STP).
TM-21 seeks methods for lumen-maintenance prediction
Devising a standardized method to predict the long-term lumen maintenance of packaged LEDs and LED modules is not an easy task, writes Jianzhong Jiao in his latest column on standards.
When lighting designers, specifiers, builders, and contractors evaluate or implement LED lighting products, just as with any other lighting technology, they want to know how long those LED lighting products will last. More specifically, they need to know how long it will take, in terms of hours or years, until the light output of these products is reduced to a level where they need to be replaced. Practically, the users want to know how to predict LED lighting lumen maintenance.
Non-directional luminaires require new testing procedures for LED light engines
In his latest column on standards, Jianzhong Jiao explains why changes to the Energy Star program will require new standardized procedures to evaluate the performance of LED light engines.
As LED technology advances and becomes increasingly used in luminaires, the lighting industry has identified a need for more definitive standards to guide the design and development processes. The recently-drafted US Energy Star Program Requirements for Luminaires identifies two categories of luminaires: directional applications and non-directional applications.
LED lighting community benefits from ongoing standardization efforts
Industry input is providing valuable feedback on the LED lighting standards that have already been put in place in the USA, while further standardization efforts are continuing, writes Jianzhong Jiao.
With the beginning of a new year and many signs of economic recovery, the LED lighting industry is gaining ground, expanding revenues and working to broaden LED product knowledge and acceptance. The continued market penetration of LED lighting is also providing the industry’s standardization community with valuable, first-hand feedback from users of the technology. This is enabling various organizations to revise existing standards and to continue to develop new standards and to prescribe best practices for developing and using LED lighting products. This article updates progress on standards in the USA since our two-part series published last year.