CHAPTER 12 MEASUREMENTS WITH THE MINI-PAM
instrument overheating with longer illumination times. An alternative
possibility to vary the ACTINIC INTENSITY range is given by the
ACT-FACT function (menu point 16). This shifts all intensities up or
down.
Before starting a LIGHT CURVE recording, a sample should be
well adapted to a moderate light intensity, which is close to the light
intensity experienced by the plant in its natural environment. In this
way the requirement of long illumination periods for reaching
steady-state can be avoided. The length of the actinic-light-periods is
determined by LC-WIDTH (menu position 19). This is limited to
3:00 min in LIGHT CURVE recordings. With the 8 consecutive
illumination periods applied during a LIGHT CURVE it is advisable
not to exceed 2:00 min in order to avoid excessive internal heating of
the MINI-PAM.
A LIGHT CURVE is started either in menu position 17 via SET
or in any other menu position by double key operation ON + ∧. The
same commands apply for termination of a LIGHT CURVE. After
starting a LIGHT CURVE there is first a YIELD-determination in the
absence of actinic illumination for assessment of the maximal
quantum yield. The sample should be sufficiently shaded, such that
the external light does not contribute substantially to the PAR, which
is approximately 100 µmol quanta m
-2
s
-1
at setting 3 of ACT-INT,
when the Leaf-Clip Holder is used under standard conditions.
Intensities are approximately 20 % higher when the 90° fiberoptics
adapter is used instead of the 60° adapter (see 8.3). Another
advantage of the 90° light incidence is a more homogeneous
illumination.
ACT-INT is automatically increased during the course of a
LIGHT CURVE and YIELD is automatically determined at the end
of each illumination period, the length of which is determined by the
ACT-WIDTH. This results in a total of 9 YIELD- and ETR-values,
80
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