TM-21 Test & Report: Turn LM-80 Data into Credible LED Lifespan Claims

After your LED products complete the thousands-of-hours LM-80 test and obtain valuable raw data on lumen maintenance rate, a key question arises: How to convert this data into persuasive "product lifespan" claims for customers and the market? The answer lies in the TM-21 test and report. It is not a new experiment, but an authoritative data analysis and extrapolation methodology—a crucial bridge connecting "laboratory test data" and "market lifespan guarantees". As an expert deeply engaged in the optoelectronic device testing field, GTG Testing Group provides you with an in-depth interpretation of TM-21's core value and implementation key points.

I. What is TM-21? Why is it Inseparable from LM-80?

TM-21 is a technical standard document issued by the Illuminating Engineering Society (IES), titled Projecting Lumen Maintenance Life of LED Light Sources. Simply put, it is a set of mathematical modeling and calculation specifications, whose core task is to scientifically predict the light decay behavior of LED light sources over a longer period based on limited LM-80 measured data (usually more than 6,000 hours), and finally calculate key lifespan nodes such as L70 (the time when luminous flux drops to 70% of the initial value) or L80.

Its importance is self-evident:

• Mandatory Requirement for Regulations and Certifications: Strict energy efficiency certifications such as Energy Star, DLC in the United States, and CEC in California all mandate that lifespan claims be derived by extrapolating LM-80 data in accordance with the TM-21 method. Without a TM-21 report, LM-80 data cannot be used for formal product certification and market access.

• The Only Scientific Basis for Lifespan Claims: It provides standardized, comparable, and auditable technical support for enterprises to claim market slogans such as "50,000-hour lifespan" and "L90 > 36,000 hours", eliminating market chaos.

• Key Tool for Product R&D and Quality Control: Through TM-21 analysis, engineers can quantitatively evaluate the impact of different materials, processes, and thermal design on long-term reliability, thereby optimizing product design.

The relationship between TM-21 and LM-80 can be summarized as: LM-80 is responsible for "recording the past" (What happened), while TM-21 is responsible for "predicting the future" (What will happen). Only the combination of the two can fully outline the life curve of LED light sources.

II. Core Calculation Model and Extrapolation Rules of TM-21 Test

TM-21 is based on a core assumption: The attenuation of LED lumen maintenance rate follows a single exponential decay model during most of the lifespan. Its prediction is not arbitrary but based on strict rules:

Strict "6X Rule"

This is the most famous and important principle of TM-21. It stipulates that based on the total duration of LM-80 testing, the maximum lifespan predicted by extrapolation shall not exceed 6 times the duration. For example:

• Based on 6,000 hours of LM-80 data, the maximum extrapolation can predict a lifespan of 6,000 x 6 = 36,000 hours.

• Based on 10,000 hours of LM-80 data, the maximum extrapolation can predict a lifespan of 10,000 x 6 = 60,000 hours.

This rule fundamentally ensures the conservatism and reliability of the prediction, and also encourages manufacturers to conduct longer LM-80 tests to obtain more competitive long-term lifespan claims.

Data Fitting and Extrapolation

The standard requires the use of the least squares method to perform exponential curve fitting on data from at least three temperature points (usually 55°C, 85°C, and another optional high temperature) in the LM-80 test. Then, the Arrhenius equation is used to extrapolate the attenuation rate at high temperatures to the actual operating temperature of the product (such as 25°C or 55°C), thereby obtaining the lifespan prediction under typical use environments.

Sample Size and Data Processing

TM-21 requires that the effective sample size under each test condition for lifespan prediction LM-80 data shall not be less than 20. In calculation, the average value of the lumen maintenance rate of samples from the same batch shall be used as the fitting basis, which ensures the statistical representativeness of the results.

III. What Key Information Does a Complete TM-21 Report Contain?

A professional TM-21 report is far more than just an L70 hour count. It is a rigorous analysis document, usually including:

• Project and Sample Information: Model and production batch number of the LED package/module.

• Cited LM-80 Report: Clearly indicate the source of LM-80 test data and test conditions used.

• Data Fitting Charts: Clearly show the LM-80 measured data points and TM-21 fitting curves at different junction temperatures.

• Key Lifespan Prediction Values:

  • LpXX (Tj) @ Confidence Level: For example, "L70(105°C) > 36,000 hours @ statistical confidence level". This is the core conclusion.

  • The LED junction temperature corresponding to the prediction, which is the premise for understanding the lifespan.

• Extrapolation Limit Statement: Clearly state that the predicted lifespan does not exceed 6 times the LM-80 test duration, complying with standard requirements.

• Calculation Parameters and Assumptions: List the model parameters used, extrapolation temperature, etc.

IV. Common Misunderstandings and Challenges

Misunderstanding 1: "TM-21 Test" is a separate experiment.

Clarification: TM-21 itself does not involve laboratory testing; it is a post-analysis service for existing LM-80 data. However, in the industry, "conducting lifespan prediction analysis in accordance with the TM-21 standard" is often referred to as "TM-21 test" for short.

Misunderstanding 2: The longer the extrapolated lifespan, the better.

Clarification: Under the 6X rule, a longer extrapolated lifespan comes from longer LM-80 measured data. A 60,000-hour lifespan predicted based on 10,000 hours of data is far more credible than a "long lifespan" forcibly extrapolated only based on 6,000 hours of data.

Challenge: How to choose the most favorable declared temperature point for the product?

Analysis: For every 10°C decrease in LED junction temperature, its theoretical lifespan may be extended several times. TM-21 analysis needs to combine the actual thermal design of the product to select a junction temperature for prediction that is both authentic and credible (verifiable through thermal testing) and can reflect the product's advantages, which requires profound application engineering experience.

V. Choose GTG Testing Group for Credible Lifespan Prediction

Faced with complex model calculations and certification requirements, choosing an experienced partner is crucial. With comprehensive capabilities in the LED optoelectronic testing field, GTG Testing Group provides you with an end-to-end solution:

• One-Stop LM-80 + TM-21 Service: We not only provide long-term LM-80 testing that complies with IES standards but also, after the test is completed, professional engineers immediately launch TM-21 data analysis to quickly generate authoritative reports that can be directly used for certification applications such as DLC and Energy Star, achieving seamless connection.

• Accurate Thermal Management and Lifespan Optimization Consulting: Our engineers can help you analyze TM-21 prediction results, understand the sensitive relationship between thermal design, drive current, and product lifespan, and provide data-driven professional suggestions for your product optimization.

• Certification Compliance Guarantee: We are well-versed in the latest requirements of certification bodies such as DLC for TM-21 reports, ensuring that the format, content, and statements of the report fully comply with specifications, avoiding certification delays or rejections due to report flaws.

Conclusion

Today, as the LED lighting market shifts from "competing on price" to "competing on quality and reliability", a lifespan report based on rigorous LM-80 testing and standard TM-21 analysis is the hardest technical business card for your products. It is not only the key to opening high-end markets but also the confidence for your long-term commitments to customers.

Contact GTG Testing Group immediately, and let us use scientific "prediction" to endow your LED products with trustworthy long-term value.