HANSATECH FMS1, Manual

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10 FMS 1 - Fluorescence Monitoring System
© 2017 Hansatech Instruments Ltd
Fig. 1-1 . Room temperature chlorophyll fluorescence emission spectra. (Adapted from Krause and
Weis 1984)
Accurate determination of fluorescence requires a detection system which is sensitive to
fluorescence wavelengths yet blind to the actinic (or excitation) light which drives photochemistry.
In continuous excitation instruments such as the Plant Efficiency Analyser signal discrimination is
achieved using a custom designed 650 nm actinic light source to drive photochemistry; optical
filtering of the detector prevents detection of non-fluorescence wavelengths of light.
Unfortunately such systems must be shielded from ambient light during use, otherwise the red /
far-red component of day-light will be super-imposed on the fluorescence signal.
This problem is avoided by the FMS 1 as it uses an electronic method, commonly referred to as
modulated fluorometry, to separate actinic light from the fluorescence signal (Ögren and Baker
1985). During measurement the tissue sample is exposed to a pulsed amber (or optional blue) 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 FMS 1 allows three types of light signal to reach the detector:
·
ambient light of fluorescence wavelengths,
·
non-pulsed fluorescence signal induced by the ambient light,
·
and 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 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).2.