This article was published in the February 2013 issue of LEDs Magazine.
View the Table of Contents and download the PDF file of the complete February 2013 issue, or view the E-zine version in your browser.
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 solid-state lighting (SSL) 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.
In the general lighting industry, most of the components used in lighting products have been standardized by ANSI such as bulb shape, base, etc. Moreover ANSI has defined all major characteristics, such as voltage, wattage, etc.
LEDs for lighting applications, on the other hand, are still rapidly evolving. At least for now, ANSI has decided not to standardize LED package shape, footprint or other physical parameters, which might restrict further technology and product development. Instead, the proposed ANSI LED datasheet standard seeks to standardize the information being communicated between LED manufacturers and the rest of the industry to ensure that fair and consistent comparisons can be made by LED users. In developing the ANSI LED datasheet standard, the ANSI Working Group proposed: “The purpose is to specify the standardized white LED package datasheet, or data reporting format, as the means of communication between LED package producers and users. The defined contents and format of the datasheet shall be followed.”
There are some who argue the necessity of such standardization. One concern is that a standardized datasheet may bury some liabilities for the claims made by LED manufacturers. Another concern is whether there are sufficient standards to be referenced when obtaining or measuring the characteristics and properties listed in the datasheet. After extensive discussions, however, the experts from participating LED manufacturers principally agreed that an ANSI standard datasheet can be a practical approach which will benefit the SSL industry. In addition, the establishment of some critical standards for testing LEDs will be largely helpful for LED manufacturers in consistently obtaining the LED characteristics to be listed in the datasheets.
Based on a broad view of datasheets currently published by major LED manufacturers and a general consensus from LED industry experts, the contents of the proposed ANSI LED standard datasheet are defined and grouped into three areas: performance and operational characteristics; physical and electrical connection characteristics; and usage recommendations. The standard also recommends that the performance characteristics be obtained by the established (or to be established) industry standards. For example, the photometric and colorimetric characteristics should be measured by IES LM-85 (to be published); thermal characteristics should be measured by JEDS51-51; and lumen and color maintenance should be measured by IES LM-80. The standard datasheet will also list optional characteristics that LED manufacturers may want to, but do not necessarily need to disclose.
In the performance characteristics area, the standard datasheet first addresses photometric performance. LED manufacturers are required to provide information for correlated color temperature (CCT) versus luminous flux, color binning, luminous intensity distribution, luminous flux changes versus forward current and versus temperature, color changes versus forward current or versus temperature, and luminous efficacy versus forward current (as optional).
Some information is to be presented in a table format, and other in a graphic format. For example, for each listed CCT, whether it is within, or in addition to ANSI C78.377 specifications, LEDs luminous flux, CRI values and corresponding product codes are listed in a table format. Another example is that the LED spectral power distribution (SPD) is provided in a graphic format. Even though SPD may not be directly used to design LED lamps or luminaires, it has been widely acknowledged that LED users, including lighting designers, find value in reviewing SPD information. The luminous intensity in angular or spatial distribution is also presented in the graphic format.
It is widely expected that LED lumen and color maintenance information is needed for designing SSL products. However, this information can take over eight months of LM-80 testing to become available. As such, when new LEDs are launched for production and the corresponding datasheets are published, lumen maintenance test data is typically not yet available. Thus, the ANSI standard does not require lumen maintenance information to be provided on the datasheet. LED manufacturers have the option of providing this information if the previous LM-80 data and TM-21 projection for lumen maintenance of a similar LED product may be used as a reference.
Because LEDs are temperature dependent devices, thermal degrading is a critical design element. As such, all temperature related characteristic changes will be listed in the datasheet, often in a graphic format.
For the operational characteristics, the datasheet will list operating limits, thermal and electrical characteristics, forward voltage versus forward current, forward voltage binning, forward current versus temperature, and forward voltage versus temperature.
Next, the datasheet covers the physical and electrical connection characteristics including mechanical characteristics and electrical diagram. It is required that the LED’s physical properties, such as dimensions, tolerances, locations of optical center, anode and cathode, thermal pad, and electrical connections, be shown in a graphic format, so users can visualize the LED’s physical appearance. The electrical diagram that indicates external electrical connection points is also required and a diagram of the internal diode is recommended. This information helps users properly connect LEDs to the overall electronic systems used in LED lamps, light engines or luminaires.
The datasheet also describes the usage recommendation. As the LED assembly process can have an impact on overall performance, a soldering temperature profile must be provided with the acceptable temperature variation versus time for the LED during the soldering process. Exceeding the allowed temperature during soldering can induce short term damage or a long term impact on LED lumen maintenance.
LED packing information is also needed for users to purchase LEDs. This information may include mechanical diagrams that show dimensions, number of LEDs per package and packing format – if LEDs are packed as tape and reel, tray, tube, or another format. Optionally, the standard also recommends LED manufacturers provide information for how the LEDs should be handled, including equipment, ESD, etc., as well as what the environmental conditions should be for storage.
The intent of the ANSI LED standard datasheet is to ensure LED manufacturers provide accurate, consistent and reliable product information, including the order or sequence of that information. It is not ANSI’s desire to put additional burdens on LED manufacturers when establishing standard datasheets and the ANSI Working Group is diligently working to achieve the balance between benefits and burdens of such standardization. All parties involved hope that consistent communication – the ANSI LED standard datasheet – between LED manufacturers and users will be a valuable tool to further assist the growth of the SSL industry.