Glossary of Fluorescence Terms
CIRAS-2 Operator's Manual Version 2.04
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Fo‟
(light-adapted
fluorescence
origin)
Fod
Signal in the light-adapted state
when all PSII reaction centres and
electron acceptors are fully re-
oxidised using a far-red light source
and are therefore “open” for
photochemistry.
PSII electron acceptors are
transiently re-oxidised by
removing the actinic source
whilst exposing the sample
to a short pulse (approx. 3 s)
of far-red light. This
preferentially excites PSI
drawing electrons out of
PSII. The fluorescence
minimum is tracked and
logged as Fo‟.
Parameter
Alternative
Name
Definition
Measurement Method
Fv‟/Fm‟
PSII antennae
efficiency
Derived from (Fm‟-Fo‟)/Fm‟.
Probability that energy absorbed by
PSII antennae molecules reaches
the PSII reaction centre.
Requires measurement of
Fm‟ with a saturating pulse
and Fo‟ with far-red only
illumination. Automatically
calculated.
PSII
Y
Yield
Genty
Parameter
Quantum efficiency of light-use by
PSII
i.e.
number of PSII reaction events / no
photons absorbed.
Derived from (Fm‟-Fs)/Fm‟
Measure steady state
fluorescence signal (Fs),
apply saturating pulse to
determine Fm‟.
qP
(photochemical
quenching)
Derived from (Fm‟-Fs)/(Fm‟-Fo).
Proportion of absorbed energy used
by photochmical processes.
Measure dark-adapted Fo,
light-adapt, measure Fs and
apply saturating pulse to
determine Fm‟.
qNP
(non-photochemical
quenching)
qE
qN
Derived from (Fm-
Fm‟)/(Fm-Fo).
Proportion of absorbed energy
dissipated by non-photochemical
processes, principally heat
emission.
Measure dark-adapted Fo
and Fm. Light-adapt and
apply saturating pulse to
determine Fm‟.
NPQ
Alternative expression of non-
photochemical quenching.
Derived from (Fm-
Fm‟)/Fm‟
ETR
(electron transport rate)
Derived from (
PSII
* incident PAR *
0.5 * leaf absorption)
Estimated rate of electron transport
flow within the chloroplast.
Measure
PSII
simultaneously
with incident radiation in
sample via PAR sensor on
leaf-clip. Leaf-absorption
factor must be measured
separately with an
integrating sphere.
