Double-Modulation Fluorometer FL 6000 (formerly FL 3500) measures Chl-fluorescence signal with a time resolution of up to 1 µs in the Fast FL 6000-F version or up to 4 µs in the Standard FL 6000-S version. Measured fluorescence emission is excited by a set of light-emitting diodes that generate short measuring flashes; the photochemistry is driven by single-turnover flashes or by continuous actinic irradiance. Chlorophyll fluorescence is detected by a PIN photodiode and digitized by a 16-bit A/D converter. The instrument supports Pulse Amplitude Modulation measurements and, at the same time, can capture fast OJIP transients or perform rapid measurements of Q_A- reoxidation kinetics, S-states, or of the effective antenna size. The major novel feature of this fluorometer is the capacity of the instrument to generate rectangular actinic flashes of extremely high power. Full reduction of Q_A acceptor can be achieved within 25 µs and the instrument can measure fluorescence induction during such a single-turnover saturating flash. This technique is used to determine the effective antenna size of the Photosystem II as well as its heterogeneity and connectivity without disturbing the measured system by DCMU or other herbicides. Photosynthetically active samples, either suspensions, leaves, or even corals, can be investigated for their photochemical yields, quenching parameters, state transitions, or for the kinetics of photosynthetic redox reactions.

PSI fluorometers measure:

Various Chl fluorescence parameters, ratios, and quenching coefficients that provide information on the functionality of the photosynthetic apparatus. These are five basic fluorescence parameters - F₀, F_m, F₀, F_m', F_s - and a number of differences and fluorescence ratios. Such as, for instance:

• Maximum quantum yield of Photosystem II
• Non-photochemical quenching NPQ
• Effective quantum yield of Photosystem II
• Non-photochemical quenching of variable Chl fluorescence
• Photochemical quenching of variable Chl fluorescence

Other supported protocols:

• Flash fluorescence induction (one flash)
• Fast OJIP transients
• Rapid Q_A-reoxidation kinetics
• S-states
• Effective antenna size
• PSII connectivity (J parameter)

How PSI fluorometers measure:

Measured fluorescence emission is excited by a set of light emitting diodes that generate measuring flashes. The photochemistry is driven by single-turnover flashes or by continuous actinic irradiance. The FL 6000 has two input channels. The first channel is used for Chla-fluorescence measurements. The second channel can be optionally used for temperature reading or dissolved oxygen probe signal measurements. FAR-LED unit with 735 nm LEDs can be optionally connected to the SuperHead measuring unit. Thermoregulator TR 2000 or dissolved O₂ microelectrode A/D converter are optional accessories for measurements with the Fluorometer measuring unit.