Spatial Uniformity Of The Spectral Radiance By White Led-Based Flat-Fields

The spatial uniformity of the spectral radiance by four commercial flat-field sources relying on white Light-Emitting Diode (LED) technology were investigated in the 400-800 nm spectral range using a hyperspectral radiometer. Results showed that for most of the flat-fields the spatial non-uniformity defined by the standard deviation of radiance differences across the source area in a given spectral interval, is typically lower than 1% within 5 cm from the center of the source and not exceeding 5% within 10 cm. The corresponding impact on radiance spectral distribution indicated non-uniformity values generally lower than 1.5% within 5 cm from the center of the sources, but increasing to several percent beyond the 5 cm distance. Finally, the spectral noise of radiance measurements defined by the variation coefficient across repeated acquisitions of the same target area on the sources exhibited mean values between 0.02% and 0.1% for most of the flat-fields in the 420-700 nm interval, but reached several percents outside such a spectral region as a result of the low flux from white LEDs. The above non-uniformity features of white LED-based flat-fields were shown to generally outperform those of a custom flat-field built of a lamp illuminating various diffusers. These findings indicate that flat-fields based on white LED technology may be suitable radiance sources for applications whose measurement requirements are satisfied by the spectral distribution of the radiant flux by white LEDs. (c) 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement