The two versions of the JUNIOR-PAM fluorometer provide visible light of different spectral composition: the BLUE version emits between 400 and 500 nm with a maximum around 445 nm. The WHITE version shows a narrow-band blue emission peaking around 445 nm plus a broad band emission ranging from 475 to 650 nm (Fig. 1).
Both versions are equipped with a far red LED with maximal emission around 745 and an emission range from 675 to 800 nm.
Also the spectral window for fluorescence detection distinguishes the two versions. The BLUE version detects fluorescence at wavelengths > 630 nm and the WHITE version at wavelengths > 650 nm (Fig. 2).
The BLUE version is the standard type of the JUNIOR-PAM and suitable for fluorescence measurements with most eukaryotic algae and higher plants. For algae absorbing poorly in the blue, as can be the case in species of the phylum cyanobacteria, the WHITE version yield significantly better fluorescence signals than the BLUE version.