Which is more accurate in estimating LED life: LM-80 or TM-21?

　　The emergence of LED lamps has changed the entire lighting market, replacing the original halogen lamps and fluorescent lamps (CFLs) in buildings and streets. Engineers often compare LED lamps from different manufacturers and choose the best style. But how can engineers ensure that they choose the most suitable lamp?

　　LED Testing Manual Guide

　　The Illuminating Engineering Society (IES) is a nonprofit organization that publishes publications as references for lighting applications and science. It is also a co-sponsor of ASHRAE/IES Standard 90.1 and Standard 189. The society publishes many documents related to lighting and energy.

　　IES has many manuals and guides related to LEDs that can help engineers clearly identify the authenticity of the quality of LED lamps. One of the manuals is LED LUMENS-79-08 Electrical and Photometric, which establishes a set of standard procedures for testing LED products. The manual details the methods for testing lumens, luminous power, lighting intensity (candela), lighting directionality, color temperature and color rendering index (but it is limited to LED lamps and does not include LED chips , packages and modules.)

　　The LM-79-08 manual specifies the test environment and variable parameters (such as ambient temperature). It also records the relevant test data of each LED lighting product, such as the test organization, test date and lighting performance data after the test. If the situation is not certain, the uncertainty statement can be retained.

　　Lighting power is measured in lumens (amount of light produced) per watt. Over the past few years, LED power has increased from 50 lumens per watt to 130 lumens today. Generally, cool white LEDs operate more efficiently than warm white LEDs. In contrast, traditional lamps have lower power. Incandescent bulbs produce 15 lumens per watt, CFLs produce 60 lumens per watt, fluorescent tubes produce 100 lumens per watt, and high-end metal halide lamps produce 100 lumens per watt.

　　LED power has increased dramatically in recent years, and it is estimated that LED lamps that produce 100 lumens per watt will soon be popular everywhere. Researchers in the laboratory have successfully made LED bulbs that produce more than 200 lumens per watt. LEDinside pointed out that Cree, a major American manufacturer, has recently announced a commercial LED bulb prototype with 170 lumens per watt, and is negotiating with the industry on the time and quantity of actual production.

　　life cycle

　　LED lamps have a very long lifespan. Like other light bulbs, LED bulbs will gradually reduce their light output over time. However, unlike other light bulbs, LED bulbs gradually dim rather than burn out, unlike other light bulbs that suddenly break down. Improper temperature, power and moisture are the main causes of LED damage and are also the factors that determine the lifespan of LEDs.

　　IES has another manual guide specifically for LED light sources and modules - LUMENS-80-08 Measuring Lumen Maintenance of LED Light Sources, which establishes a set of procedures for detecting the life of LEDs (and when the light level becomes dim enough to be eliminated).

　　The life of an LED is determined by the number of hours it takes for the power to drop to a certain threshold, also known as lumen maintenance. The LM-80-08 manual mentions two different standards used by the industry, one that states that a bulb is unsuitable for continued use if its lumens are less than 70% of its original value, and the other that states that it is no longer usable if its lumens are less than 50% of its original value. The first standard (L70) is mainly used by general lighting LED lamps, while the second standard (L50) is used by decorative LED lamps. These two LED life standards were developed by the Alliance for Solid-State Lighting Systems and Technologies (ASSIST) of the Lighting Research Center.

　　For example, after using an LED lamp that has passed the LM-80-08 test and claims to have passed the test for more than 30,000 hours, the lumen number is still 70% higher than the original light output, which means that passing LM 80 not only meets the basic light decay requirements, but also has better performance. The current LM80 test project on the market is very expensive, about $15,000, because it takes thousands of hours of lighting to get the parameters and accurate data for the light decay test. The manufacturers who can afford to do this are generally medium-sized and large manufacturers.

　　Regarding LED life, LM-80-08 sets standard test environment and variable parameters. The test report must cover important data and the test process.

　　The life of a typical incandescent bulb is 1,000 hours; CFL is 8,000 to 10,000 hours; the best fluorescent tubes can reach 30,000 hours. The average life of a general metal halide lamp is 7,500 to 20,000 hours (the life standard is L50), and the life of a general LED bulb is 30,000 to 50,000 hours (the life standard is L70).

　　LM-80-08 does not provide a method for estimating LED life. IES's Technical Memorandum - TM-21-11 Projecting Long Term Lumen Maintenance of LED Light Sources recommends calculating the maintenance of LED light sources from the data obtained during the LM-80-08 test process. This memorandum is used to estimate the maintenance of LED light sources and lifespans greater than 6,000 hours. The IES LUMENS-80 manual specifies three different test ambient temperatures. TM-21 can estimate the maintenance of LED light sources based on three test results.

　　Verification and testing

　　Engineers should confirm that LED manufacturers' light sources have passed the test standards based on IES guidelines LUMENS-79-08 and LUMENS-80-08. Lamp manufacturers should provide lumen maintenance data based on IES TM-21. Ideally, an impartial and reputable third-party qualified laboratory should be used to test LED lamps.

　　Engineers should ask LED manufacturers to provide IES LUMENS-79-08 and LUMENS-80-08 test process data and test result evaluation reports. The data should be consistent with the published LED specifications. Engineers should also find out the warranty period of the lamps and the manufacturer's credit and history.

　　It is helpful for new products to pass the LM-80 test, but the testing time may take longer because the complete testing process takes 6,000 hours, which is also the main reason why the LM80 test price is high.