Brief Introduction to Chlorophyll Fluorescence
CIRAS-2 Operator's Manual Version 2.04
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pulsed amber LED light source (the modulating beam) which induces a pulsed fluorescence signal from
the sample under conditions where ambient light is excluded (A, Figure 2). When ambient light is applied
the optical filtering of the CFM allows three types of light signal to reach the detector:
i)
ambient light of fluorescence wavelengths,
ii) non-pulsed fluorescence signal induced by the ambient light,
iii) pulsed fluorescence signal induced by the modulating beam (B, Figure 1-2).
Addition of ambient light changes the physiology of the sample, altering the proportion of energy that is re-
emitted as fluorescence. Thus the magnitude of the peaks of the pulsed fluorescence signal that are
induced by the modulating beam will reflect changes in sample physiology. It is these signals that the rapid
pulse peak tracking electronics amplify and measure; ambient and non-pulsed fluorescence signal are
discarded (C, Figure 1-2).
Figure 1-2.
Fluorescence signal detected by the CFM under modulating beam only
conditions (A), under actinic light plus modulating beam before (B) and after (C)
the rapid pulse peak tracking electronics.
The pulsed fluorescence that is induced by the modulation beam is effectively used to probe the efficiency
of light-use for photosystem II photochemistry. Clearly it is important that the measuring technique itself
does not induce changes in the physiology of the sample under investigation.
Exposure of a sample to a powerful pulsed light source may be expected to introduce a significant artifact
into the measurement. However, CFM-1 has been specifically designed to avoid such problems by using
a modulating beam of very short duration pulses (1.8 µsec) with long off period between pulses. The net
result is that the integrated amount of radiation incident upon the sample from the modulating beam is
0
A
B
C
A
mb
ien
t L
igh
t
S
ign
a
l (
Rel.
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n
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Un-pulsed
Fluorescence
P
ul
s
ed
fl
uo
res
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en
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e
Содержание CIRAS-2
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