What testing is needed for an LED?

-November 26, 2012

The recent ban on the incandescent light bulb, government incentives, and the ingenuity of industry experts have all played a role in LEDs becoming the predominant new product in the North American lighting market today. As this technology continues to rapidly evolve, lighting manufacturers and others involved in the industry are finding it increasingly challenging to validate product claims and keep up with industry standards and testing requirements.

As with most new technology, LEDs tend to be more costly than their conventional counterparts – the fluorescent light bulb – though they have been significantly going down in price. In an attempt to offset the price, lighting manufacturers highlight the performance of their products, some claiming 10-year lifespans compared to the typical one-to-two-year lifespan of traditional lighting products. Since these marketing claims are difficult to prove, new criteria has recently been developed for LEDs to help manufacturers avoid customer backlash and negative publicity and provide verification for their products.

Standards and Specifications
In order for lighting products to be sold in the market, they must meet certain national and international industry standards. The standards identify recommended test methods, which are typically the same among third party testing laboratories. Some of the key lighting performance standards for North America include:

•    IESNA LM-79-08 – Electrical and Photometric Measurements of Solid-State Lighting Products
•    IESNA LM-80-08 – Measuring Lumen Maintenance of LED Light Sources
•    IESNA LM-82-12 – Characterization of LED Light Engines and LED Lamps for Electrical and
    Photometric Properties as a Function of Temperature
•    IESNA TM-21-11 – Projecting Long Term Lumen Maintenance of LED Light Sources

In turn, there are several North American and international energy efficiency programs, each with its own specifications. Some of the most prevalent programs in North America include ENERGY STAR®, Natural Resources Canada (NRCan), California Energy Commission (CEC), U.S. Department of Energy (DOE) Lighting Facts, DesignLights™ Consortium (DLC) and Municipal Solid State Lighting (MSSL). Since specifications reference specific standards, the criteria can vary depending on the individual program but the standards for testing and measurement are the same.

One initiative worth highlighting is the DOE-sponsored Lighting Facts Label, which is a new labeling standard currently mandatory on all packaging for screw-based replacement lamps including incandescent, halogen, CFL and LED models. Modeled after the “Nutrition Facts” Label on modern food packages, the Lighting Facts Label provides information on a light’s brightness, energy cost, life expectancy, light appearance (warm or cool) and wattage. The new label was designed to provide a uniform and user-friendly way for consumers to review product specifications and make product comparisons.

The Testing
Third-party testing plays a key role in product certification. Nationally Recognized Testing Laboratories (NRTLs), organizations approved by OSHA, provide unbiased assurance that products meet the requirements of industry standards and energy efficiency programs and confirm consistency through proficiency tests and factory inspections.

Typical areas of testing and measurement include total luminous flux, luminous efficacy, correlated color temperature and electrical power consumption, among others. While most tests are done directly within the lab, they can also take place at a company’s manufacturing facility if necessary. In that case, the manufacturer must participate in a data acceptance program with the third party lab, which is an industry known methodology that ensures testing results remain unbiased. Data acceptance programs can be used for both performance and safety testing.

Figure 1: A Type C goniophotometer from Intertek’s laboratory in Cortland, N.Y.

When testing LEDs, an integrating sphere and a Type C goniophotometer are the two main types of equipment used. The integrating sphere provides certain key values such as color temperature, and the goniophotometer identifies how the light will project. For example, if a product is placed in a 360° plot, the goniophotometer will tell what area will light up at a given distance, allowing architects to project light paths and determine where they should place lights.

Figure 2: An integrating lighting sphere from Intertek’s laboratory in Cortland, N.Y.

Equipment functions oftentimes overlap. For example, total luminous flux is measured in the integrating sphere for LED lamps or small luminaires and in the goniophotometer for larger luminaires. To perform this and other tests, both the integrating sphere and goniophotometer require certain accessory equipment including an AC/DC voltage source, voltage regulator and temperature probes to energize the lights and take measurements.

The quality of the testing is only as good as the quality of the equipment used. While manufacturers are able to conduct their own testing, third-party testing laboratories are required to have equipment that is calibrated to ISO 1705, which is important because small variances in tolerances on a piece of equipment can affect the measured value. For LEDs, a very specific tolerance is required for the input source, directly affecting the output values produced. Making sure the test is conducted under the right conditions is also critical. Room ambient temperature should be between 25°C ± 1°C, measured at no more than 1 meter from the product and at its same height. The temperature sensor should also be shielded from direct optical radiation from the product. In addition, the mounting of the product is key as location can affect heat flow away from the product.

>>The Challenges

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