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New LED Calibration Standard BN-LLSF-2P to match “CIE Reference Spectrum L41” according to CIE 251:2023

In photometry and colorimetry, standard illuminant A light sources have exclusively been used for calibration for decades. Due to the dominant application of LEDs in the field and the fade-out of tungsten lamps as calibration sources, new concepts are needed. With CIE 251:2023 the CIE published in February 2023 a recommendation for an LED reference spectrum named "CIE reference spectrum L41".

The shape of this spectrum is based on available LED illuminant consideration as well as minimum error considerations in terms of spectral mismatch errors of photometers. However, it was not designed to match to an existing LED on the market. The idea of this source is for it to be in addition to standard illuminant A for photometer calibration, especially for LED measurements. The document also states information about typical magnitudes of spectral mismatch errors with V(λ)-filtered photometers in measurements of LEDs as well as other types of light sources. This is done under the assumption that CIE reference spectrum L41 is used for photometer calibration instead of CIE standard illuminant A. Finally, the document introduces a quality metric for selection of white LEDs as physical LED standard sources.

On this basis, Gigahertz-Optik developed the LED-based standard BN-LLSF-2P which is perfectly suited for calibrations of photometers according to document CIE 251:2023 since it is following the CIE reference spectrum L41. The source matches the reference spectrum very well with just minor deviations as indicated by the spectral distribution mismatch index of fsf,L41=0.016. The standard BN-LLSF-2P can be used both as an illuminance calibration standard for photometers as well as a luminous flux standard in combination with an integrating sphere in 2 Pi geometry. The standard is offered together with a calibration by Gigahertz-Optik’s in-house ISO 17025-accredited calibration laboratory, which guarantees highest quality and standards



Spectral distribution of BN-LLSF calibration source compared to CIE reference spectrum L41 (CIE 251:2023)