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Changing Fv/Fm measuring parameters -
One can change the test parameters by pressing the box in the upper left hand corner of
the measuring screen.
Fv/Fm measuring Screen 1p Fv/Fm Test Setup Screen
Setting the modulation light source intensity- It is adjustable between 0.1:mol
and 1 :mol when using a dark clip. adjustments are made in 5% increments between 5%
and 100%. The correct setting depends upon the distance from the sample , and nature of
the sample.
The modulation source should be optimally set to allow pre-photosynthetic antennae
fluorescence measured as the Fo value. It must be set at a value that too low to drive
photosynthesis. If it too high, it will cause an error in measured Fv/Fm values
If the intensity is too high, it can be seen as a slow rise in “fluorescence signal” visible on
the set up screen or the “Ft” value visible on the Fv/Fm measuring screen. After setting
the modulation intensity, watch the Ft value. If the average value increases over a 30
second period, the intensity should be reduced.
For correct testing of the modulation intensity setting, put a leaf, of the type to be
measured in a study, in a dark clip, and dark adapt. Place the fiber optic probe all the way
into the dark clip, and expose the dark adapted area of the leaf to the modulated light.
The modulated light is always coming out of the end of the fiber bundle when a
measuring screen is viewed. The modulated light is set correctly if it is high enough to
get a fluorescence measurement when the measuring button is pressed, but not too high
so that it is driving photosynthesis. A setting that is too high will give an incorrect
reading of Fo, a value that should be a pre-photosynthetic measurement. The setting is
linear. The “Gain” should be as low as possible for the best signal to noise ratio.
New -automated modulation light set up
“Auto Gain” – On the set up screen, this option automatically adjusts the modulated light
setting to a detection range that will work for the sample. It is known from experience
that this level does not drive photosynthesis on tested samples. Dark adapt a sample to be
tested in either a dark clip or with a shrouded PAR clip. Press “Auto Gain” with the leaf
sample in place, and the instrument automatically goes through a routine that sets the
modulation intensity correctly.
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