Walz MINI-PAM-II, Manual, Page: 18 / 130

Chapter 4 Components and Setup
12
hole. In the latter case, the leaf can be held between the folded
parts of the clip.
The distance between fiberoptics exit plane and sample has
considerable influence on signal amplitude and effective light in-
tensities (Fig. 4, page 12). With a 60° angle between sample
plane and fiberoptics, the distance between leaf surface and fiber
optics varies. Hence, the leaf surface is exposed to slightly het-
erogeneous light intensities when actinic light is applied
via the
fiberoptics. A much more pronounced intensity gradient exists in-
side the leaf due to shading by the top chloroplast layers. In es-
sence, the measured signal will be dominated by that part of the
leaf which receives maximal intensity, as this also is most strong-
ly excited by the measuring light and emits most of the fluores-
cence which is received by the fiberoptics.
Fig. 4: Relationship between signal amplitude/light intensity and distance
between fiberoptics exit plane and sample