Walz MINI-PAM-II, Manual, Page: 52 / 130

Chapter 6 Hints
46
6.3 F
0
Fluorescence
Usually, measuring light intensity is adjusted to reach F
0
fluores-
cence levels around 500 mV (for a definition of F
0
see Section
5.1.1, page 32). Theoretically, the F
0
should stay below 640 mV.
The latter upper value is derived from the assumption that the
maximum F
V
/F
M
of any sample is 0.84 und from the fact that sig-
nal saturation occurs at 4000 mV (see equation below, Table 5).
If required, measuring light can be adjusted (Fig. 39, page 72).
Table 5: Maximum F
0
of a Dark-acclimated Leaf
( )
( )
( )
640
84 . 0
) (
) (
0
0
=
=
−
=






Max
Max
M V
Max M
Max
Max M
Max
M
V
F
F F with
F
F F
F
F
(F
M
)
Max
, maximum possible F
M
value =
4000.
(F
0
)
MAX
, unknown maximum F
0
value
(the F
M
associated with this F
0
, or with
smaller F
0
, is not saturating).
(F
V
/F
M
)
Max
, assumed maximum possible
PS II photochemical yield.
At low signal levels, signal height can be increased by increasing
measuring light intensity. At too high intensities, the measuring
light might drive photosynthesis to some degree. Therefore, test
if switching on measuring light results in a stable signal or if any
signal increase occurs. In the latter case, the effective measuring
light intensity must be decreased either by reducing the ampli-
tude of measuring light (measuring light intensity) or by reducing
measuring light frequency or both (Section 7.3.1, page 70).