LED datasheet standard enhances manufacturer-developer communications (MAGAZINE)
An ANSI-accredited standards group within NEMA is publishing a standard describing the parameters and characterizations required on LED datasheets, reports Jianzhong Jiao, and the result will allow developers to more easily contrast and compare LEDs from multiple vendors relative to specific application requirements.
The American National Standards Lighting Group (ANSLG), an American National Standards Institute (ANSI)-accredited standard committee administrated by the National Electrical Manufacturers Association (NEMA), was preparing to publish a standard on LED datasheets as this issue of LEDs Magazine went to press. Most likely the standard is available as you are reading this article, as it was slated to be published by the end of March 2016. Here we will summarize the goals of the effort, and the ultimate requirements in parameters and characterizations of packaged LEDs that will allow solid-state lighting (SSL) developers to more easily digest and compare LED data relative to end application requirements.
ANSI formed an ad hoc group to develop LED datasheet standards in early 2012. In the February 2013 issue of LEDs Magazine, this author published an article "ANSI works to standardize LED datasheet for white LEDs" that described the initial effort and provided background on ANSI's work. LED datasheets are a communication tool widely used between LED manufacturers and users or SSL product developers. The purpose of standardizing the LED datasheet is to promote more effective communication. The document was by no means intended to convey any intention to standardize packaged LED components. Moreover, experts in the ANSI committee fully understood that LED technology and applications would continue to evolve.
In over three years of hard work developing this document, one of the major debates in the committee was focused on the mandatory datasheet contents in ANSI standards. In practice, LED datasheets published by the LED manufacturers are for the purposes of both education and marketing. Often, the datasheet contents, language, and certainly the format vary significantly from one LED manufacturer to another.
Scope of standards effort
To standardize the communication between manufacturers and users, the mandatory contents of a datasheet should reflect the basic needs in designing LED-based lighting products. For additional and optional information deemed useful and beneficial to users, ANSI usually does not provide specifications in regard to how and what should be included; however, the ANSI standard does not exclude them, either.
The scope of the ANSI datasheet standard states, "The purpose of this standard is to specify the standardized white LED package specification sheet, or data reporting format, as the means of communication between LED package producers and users in general illumination applications. The minimum defined contents and format of the specification sheet are provided. Manufacturers can include additional information." The standard provides the general requirements for the title and includes the brand name and product name. The requirements for the graphs used in the datasheet include scales, colors, legends, units, font size, etc. This helps to maximize perspicuity to readers as well as simplifying machine scanning when required.
The consideration for the information to be reported in the LED datasheet is based on the purpose of designing an LED lamp or luminaire. LED users require the information to select LEDs when determining the optical, electrical, thermal, and mechanical design strategies. LED lighting product design is an integration and balance of optical, electrical, thermal, and mechanical strategies and approaches.
Usually, the first step of the design is the optical design feasibility, which is to achieve the function of a lamp or luminaire - how much light, where the light goes, and what color characteristics are required of the light. The optical design feasibility is based on the selection of LED performance characteristics; thus the ANSI datasheet standard first lists the reporting requirements for the LED's performance characteristics.
LED performance characteristics
The LED's performance is dependent on two basic variables: junction or case temperature and forward current. And in all applications, the LED performance level decreases when the temperature increases. Because of this fact, any performance information listed in the datasheet should always be clarified for the specific junction or case temperature, as well as a specified forward current.
Usually, white LEDs provided by an LED manufacturer come with a range of the correlated color temperatures (CCT) offered in the line. For a given type or model of an LED, its luminous flux for each CCT may differ due to the technologies used in the LED die and phosphors, as well as the quality process for manufacturing them.
The first reporting performance characteristic in the ANSI LED datasheet is the luminous flux associated CCT. CRI, on the other hand, can also vary within a given CCT; therefore, the CRI needs to also be listed. Because LEDs are produced with distributions of variations in luminous flux and color, for one CCT, there is a distribution of the color variation, which is binned by the LED manufacturer. The assigned color bin code must be reported. Moreover, CCT and CRI are derivatives of the LED's physical characteristics fully captured by the spectral power distribution (SPD). SPD is now often reviewed by the lighting design community so the ANSI datasheet standard also requires SPD to be reported.
Optics and thermals
The datasheet must also accommodate the system-design mission of the product developer including in optical, thermal, and electrical disciplines. For instance, in choosing the design strategies or approaches for the secondary optics, such as lenses, reflectors, light pipes, and other optical elements used in an LED lamp or luminaire, the LED's luminous intensity distribution must be known and is used as an input parameter. For this reason, the ANSI datasheet requires manufacturers to report the description for luminous intensity distribution.
Parallel to the optical design is the electrical and thermal design that is impacted by LED selection. The information required for setting up the electrical and thermal design strategies is the LED light level or luminous flux change when forward current or temperature changes. For this purpose, the ANSI standard requires the relationships of luminous flux versus forward current and luminous flux versus temperature to be provided.
In designing LED lamps and luminaires, the selection of LEDs also involves developers considering how LEDs will be operated in a final lighting product. The next section of the ANSI datasheet standard requires listing of the LED operational information. This information includes operation limits such as maximum junction or case temperature, maximum forward current, and maximum reverse voltage. A few critical parameters can affect the LED lamp and luminaire electrical and thermal design: the LED's thermal resistance, forward voltage, electrostatic discharge withstand voltage, forward current versus forward voltage, and forward current versus temperature. These parameters must be reported per the ANSI datasheet standard.
The mechanical design information is equally important when selecting LEDs. The required information includes: LED overall dimensions and tolerances, location of the optical center, the anode, the cathode, the thermal pad, and more. Furthermore, to be design-friendly, the LED's electrical diagram is to be provided.
Next, the ANSI standard provides recommendations for LED product handling and package information. In particular, in today's applications, most of the LEDs are surface-mount devices (SMD), and the reflow process is used in soldering the LEDs to printed circuit boards (PCBs). Therefore, the ANSI standard requires that reflow characteristics and recommended reflow process methods be reported because product assembly can impact performance and reliability.
Honest and accurate reporting
Last, the data listed in an LED datasheet should be reliable, credible, and objective. For this purpose, the ANSI standard requires the LED manufacturers to report the method used to obtain the photometric and chromaticity data. As for the thermal data, the ANSI standard refers to the corresponding JEDEC standard. JEDEC is an organization that sets component standards in the microelectronics industry.
The ANSI LED datasheet standard is very much based on the need to aid and protect LED users when designing LED lamps and luminaires. The information required in the datasheet is selected for being design-friendly. This standard should unify the communication between LED manufacturers and users; and it should also simplify and bring focus to the key elements of the communication, thus making it more effective. The value and benefit of this standard will be greatly appreciated by the LED lighting community.
DR. JIANZHONG JIAO, an internationally recognized lighting expert, is an independent consultant for LEDs and lighting technologies. He has been actively involved in LED and LED lighting standard development activities, technical conferences, and industry consortia. Currently he serves on the IESNA Testing Procedures, Roadway Lighting, Computer, and Light Source Committees. He is also vice chair of the ANSI SSL Light Source Working Groups, and at present works with many other technical organizations, groups, and symposia, in addition to being a member of the Technical Panel of Strategies in Light. He can be reached at email@example.com.