Difficulties can arise with standards when the test conditions do not match those of the installed application. As an example, downlight luminaires are typically measured according to the IES LM-79 standard that requires the surrounding ambient temperature to be at 25°C. In practice, the ambient temperature generally will be higher when the light source is recessed in a luminaire. In addition, the temperature is dependent on where the luminaire is located and will be higher on upper floors where the fixture is surrounded by insulation material. This potential for higher ambient temperatures was less of an issue in the past when downlights used incandescent and halogen technologies whose performance was less sensitive to changes in temperature. But in the case of LEDs, increases in junction temperature can alter the performance. Past studies have shown that in some cases the light output reduction from the product is significant, more than 30 percent (Narendran et al., 2008), versus the LM-79 data sheet. Practitioners expecting a certain performance may be disappointed if they strictly rely on the product’s LM-79 data. While the use of testing standards has worked for incumbent lighting technologies, LM-79 may not work for SSL products because of the latter’s sensitivity to heat. Test procedures specific to the application environment are an ideal solution but much more costly than a single procedure for all applications. A compromise solution would be for manufacturers to publish data with de-rating factors for use in typical applications.
Another important aspect of standards is their quality; that is, their ability to produce reliable and realistic information about performance. Today manufacturers commonly use the IES LM-80 procedure to test the lumen depreciation of individual LEDs, but then use those data to rate the entire product life. (Labeling programs also use LM-80 test data.) In reality, a product has many more components than just the LED. Electronic drivers with electrolytic capacitors are known to have a short life, especially at high temperatures. Products claiming a life of 25,000 to 50,000 hours may not live up to such claims as a result. LM-80 test results are more appropriate for LED package manufacturers to provide to product manufacturers, not to product end users. Even though white papers have started to point out this issue (Next Generation Lighting Industry Alliance, 2011) and research is under way to develop test procedures to predict whole product life more accurately (Davis, 2012; Lighting Research Center, 2012), early adopters of LED lighting may be disappointed when products do not live up to the claims on their labels, based as they are on LM-80 results. Some SSL product manufacturers have started offering warranties for their products. This too is challenging because the terms and conditions for product replacement or cash reimbursement can be difficult to define and settle.
Other examples of industry challenges with standards include the current color standards (e.g., ANSI C78.377) that were borrowed from the CFL industry. Manufacturers grouping LEDs to single bin for a given correlated color temperature (CCT) product according to American National Standards Institute (ANSI) C78 tolerance area may find the color variation between LEDs very large, to a point that it is not acceptable for general lighting applications. Presently, some manufacturers are using tighter bins to avoid visible color difference between products.
FINDING: Additional standards or revisions to standards are needed to resolve unknowns that will otherwise be left to consumers and other lighting decision-makers to resolve, specifically test procedures and/or de-rating factors that account for higher temperature environments, where performance may vary from LM-79 data, and alternatives to LM-80 that can predict whole product life more accurately. In the case of the latter, research is under way to develop test procedures to predict whole product life more accurately.
RECOMMENDATION 4-4: (a) Manufacturers should publish data for photometric quantities and life per industry standards and de-rating factors for use in typical applications. (b) IESNA should develop a test procedure to predict whole product life more accurately. (c) ANSI should revise the color binning standard to ensure imperceptible color differences between two adjacent light sources.
In the United States, power quality is a subject of voluntary industry standards, except for electromagnetic compatibility of some lighting equipment, which is regulated by the Federal Communications Commission (FCC) at frequencies corresponding to radio and television transmissions.
The Institute of Electrical and Electronics Engineers (IEEE) sets voluntary standards for distortion of the voltage waveform in the utility supply to buildings (IEEE 519) in order to ensure that electrical and electronic equipment in the building has a reasonably clean supply of power (correct frequency, voltage, and lack of distortion). Distortion of the sinusoidal voltage waveform is of most concern and is expressed in terms of a parameter known as “total harmonic distortion” (THD),10 which is typically limited to about 5 percent. On the other hand, industry voluntary standards set limits to the distortion in the current waveform drawn by the equipment connected to the electric supply. The distortion is
10 Total harmonic distortion (THD) of the supply voltage is equal to the square root of the sum of the squares of the amplitudes of the voltage harmonic frequencies above 60 Hz divided by the amplitude of the fundamental 60 Hz voltage. A high THD (>33 percent) causes problems in three-phase power systems, because usually the dominant harmonic current is the third harmonic. The third harmonic currents add in the neutral wire of the electrical system, and in cases of high THD one can have a situation where the current flowing in the neutral wire exceeds the rating of the wire, causing overheating.