This SAE Recommended Practice provides test procedures, requirements, and guidelines for the methods of the measurement of lumen maintenance of LED devices (packages, arrays and modules). This document does not provide guidance or make any recommendation regarding predictive estimations or extrapolation for lumen maintenance beyond the limits of the lumen maintenance determined from actual measurements.
Rationale
Rationale for choosing case temperature (Section 5.2.2)
LED lumen degradation and color change over time is a temperature dependent behavior. In general, the higher the junction temperature, the faster the lumen depreciation is. The highest or maximum junction temperature is determined and recommended by the LED manufacturer based on the technologies used in the LED package. For LED users, the way in which the LEDs are designed into the automotive lighting application is based on the maximum junction temperature. Instead of setting a universal case temperature (Ts) to be tested, it is more practical for the LED producers and users, depending on LEDs and the applications, to choose a specific case temperature for a specific type of LED to be tested and reported. In the current practice, some LED manufacturers provide LED characteristics relating to case temperature, others refer to junction temperature. Because only case temperature can be directly measured, therefore it is recommended that the case temperature Ts is set, depending on the LED manufacturer’s specification, either to a temperature such that the junction temperature is within 10 °C below the maximum junction temperature claimed by the LED producers. or if the manufacturer only specifies case temperature, then it can be tested within 10 °C below the maximum case temperature.
Rationale for lumen and color maintenance testing duration (Section 5.5.4.1)
The exterior automotive lighting usage in the US for the life of the vehicle is referred to the reports UMTRI-2008-14 and UMTRI-2008-48 where a 95 percentile duty cycle was assumed which is more appropriate than average usage. In the reports, the annual usage of DRL is presented to be 382.0 h, and for the other (non-DRL) longest use lamps 107.1 h. Based on this information, the life of the vehicle lighting is estimated. If the LEDs used are expected to last the life of vehicle, the lumen maintenance test duration is recommended for 6000 h for DRL and 2000 h for other lamps.
The Lighting Standard Practices Committee is part of the Lighting Systems Steering Committee that reports to the Motor Vehicle Council (MVC). The committee is responsible for developing and maintaining SAE Standards, Recommended Practices and Information Reports related to the general support of documents in other VESG committees that are related to exterior lighting devices used on passenger cars, light trucks, vans and multipurpose vehicles. The committee monitors the development of related technologies and determines how they may be applied to general practice documents while also working to support the development of standards to aid in the application of various lighting technologies. Task forces may be developed in the future to support these activities. The committee welcomes input from OEM¿s, suppliers, consulting firms, government, academic institutions and other interested parties
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LED Light Sources Tests and Requirements Standard Part 2: LED Lumen and Color Maintenance Measurements
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LED Light Sources Tests and Requirements Standard Part 2: LED Lumen and Color Maintenance Measurements
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