Glossary of Fluorescence Terms
CIRAS-2 Operator's Manual Version 2.04
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Glossary of Fluorescence Terms
Definitions of the most commonly referenced fluorescence parameters are given below with alternative
nomenclatures.
F nought
F zero
O
(in Kautsky
terms)
Signal following dark adaptation
when all PSII reaction centres and
electron acceptors are fully
oxidised, hence “open” for
photochemistry.
Modulated System - monitor
signal under modulating
beam only from dark
adapted sample.
Continuous Excitation -
monitor induction with high
time resolution (10 µs).
Must have high time
resolution.
Peak signal following illumination
with non-saturating pulse of light.
Not generally used today as most
modern instruments have saturating
light sources which can deliver
>2,500 µmolm
-2
s
-1
.
Track fluorescence rise and
determine peak fluorescence
value.
Fm
(Fluorescence
maximum)
Fmax
(P in Kautsky
terms)
Maximum fluorescence signal from
the dark-adapted leaf following
application of a saturating light
pulse which fully reduced the PSII
electron acceptors preventing
photochemistry.
Dark adapt sample, apply
saturating light pulse and
determine maximum
fluorescence signal.
Fv
(Variable
Fluorescence)
Derived from (Fm-Fo)/Fm.
Directly proportional to the
maximum quantum efficiency of
PSII.
Proportional to the size of the PSII
electron transport acceptor pool.
Fs
(Steady state
fluorescence)
Ft
(terminal T in
Kautsky terms)
Signal under an actinic light.
Switch on actinic lamp on
modulated system.
Sometimes used to show
“terminal” fluorescence
signal when photosynthesis
is activated at the end of a
Kautsky curve.
Fm‟
(light-adapted
fluorescence maximum)
Maximum fluorescence signal from
light-adapted leaf following
application of saturating pulse
which fully reduced PSII electron
acceptors preventing
photochemistry.
Adapt sample to actinic light,
deliver saturating pulse and
track fluorescence signal.
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