SAE J1889:2019 pdf free

SAE J1889:2019 pdf free.LED Signal and Marking Lighting Devices
Section 4.1.5.2 of the 1999 document contained a note regarding photometry testing:
NOTE: Other test methods which yield equivalent results may be used. Examples include eliminating the ratio calculation and directly measuring the maximum photometric value at 1 minute (for a typical LED device where photometric values decrease with on-time) or directly measuring values at the specified on-time when the photometric measurement equipment can record near simultaneous readings at all test points. Readings at shorter on-times may also be used when the photometric output versus time performance of the device is known.
The term“relatively stable photometric output periods” was not defined in the 1999 version, but, in 2005, was determined to be +5% over an arbitrary unit of time. Actual measurement error is not known with the former definitions of photometric stability (2005 to 2015 versions of SAE J1889). In this ballot, photometric stability is bounded to limit measurement error due to the light source. The definition of photometric stability should be independent of light source and be valid for any current or future light source. LED stability is something completely different. LED stability can be defined as a percentage light output change over a fixed duration (i.e., +3% over 15 minutes).
Any photometric measurement on a goniometer has many error sources, including: calibration accuracy, detector drift,ambient light errors, positioning errors of DUT, and light source drift during the measurement duration. SAE J1889 is a recommended practice that teaches industry how to know the light source drift error is below a threshold determined by industry experts as a reasonable limit. The first four error sources mentioned describe goniometer measurement errors that are generally known to not be better than +3%. With a +3% goniometer error, defining light source drift error to be less than 0.01% or allowed to be greater than 3% is not reasonable. Also, goniometers are not the only way to measure the performance of lighting device. Camera-based photometry is also used and defined in SAE J3100. These devices record all data points simultaneously, and although camera-based measurements have their unique error sources, light source drift during measurement is not an error source. Therefore, SAE J1889 must re-define photometric stability to recognize methods of measurements other than goniometer. Other methods were recognized in the 1999 version of SAE J1889,”Directly measuring values at the specified on-time when the photometric measurement equipment can record near simultaneous readings at all test points.’SAE J1889 pdf free download.