Portable device for determining the physiological state of plants using fluorimetry and spectrometry methods

The study aims to present and validate a portable device for plant physiological analysis through combined measurement of fluorescence, transmission, and reflection spectra. The proposed approach integrates three complementary optical techniques in a single handheld device. The system includes two white LEDs for reflectance and transmission measurements, and a blue LED for fluorescence excitation. Spectral data acquisition is performed by a compact spectrometer. The measurement accuracy obtained with the portable device was validated against standard methods and reference instrumentation on cucumber and tomato leaves. A prototype of the portable device is capable of measuring reflection and transmission spectra, as well as fluorescence spectral intensity of plant leaves. The device requires minimal sample preparation while providing precise and reliable measurements. Average relative error is 23% for spectral reflectance, 19% for transmittance, and 26% for fluorescence. Correlation coefficients between spectral characteristics and chlorophyll concentration were also determined, and spectral information was reduced to vegetation indices with the choice of the optimal coefficient at different wavelengths. The coefficients of determination for pigment concentration and vegetation indices are 0.99 (cucumber) and 0.93 (tomato) in reflection mode, 0.99 (cucumber) and 0.90 (tomato) in transmission mode, and 0.99 (cucumber) and 0.83 (tomato) in fluorescence mode.