KONICA MINOLTA

The SPAD-502 measures the absorbance of the leaf in the red and near-infrared regions.
Chlorophyll has a peak absorbance in blue and red region and almost no absorbance in the
infrared region. Based on this evidence, the wavelength ranges measured are the red area
(650 nm, where the absorbance is high) and the infrared area (940 nm, where absorbance is low).
The leaf have to be inserted to measuring head with a measuring area is 2mm x 3mm.
LEDs emits red and infrared light that passes through the sample in the measuring head,
and then enters in the receptor which converts the transmitted light to analog electric signals.
Before measuring, calibration procedure is carried out: LED emits light without any sample.
After the sample is inserted in the measuring head the LEDs emit light again and the ratio of
intensities of the transmitted light is calculated.

https://www5.konicaminolta.eu/it/strumenti-di-misura/prodotti/misura-di-colore/articoli-non-piu-in-produzione/