LI-COR LI-6400, Manual

Page: 485 / 846

Calibration Issues
GaAsP Light Sensors
Using the LI-6400 18-29
3 Orient the leaf chamber
Orient it so that the incoming radiation is perpendicular to the leaf plane. The
distance from the leaf chamber to the light source should not be changed be-
tween light sensor calibration and photosynthesis measurements. This will
minimize errors due to radiation geometry and view factors.
4 Set the Light Source to
Sun + Sky
This will apply no correction factor for your calibration readings.
5 Record the readings
Note the PAR values Q
c
(ParIn_µm) and Q
x
(ParOutµm)
6 Compute the correction factor
The correction factor f
a
is
(18-1)
7 Enter the new value
Select
"Light Source Control"
in the Config Menu, press labels , then press
Edit StdFile
(
F2
). Add your new correction factor to the list, as shown in
Figure 18-23. YouÕll need a name in double quotes, followed by the f
a
value,
followed by a guess at the absorbed energy conversion factor (use 0.2 unless
you know better).
Note: We do not recommend using an LI-190 quantum sensor to calibrate, or
even accurately measure, the LED light source output because the drop off in
quantum sensor sensitivity near 700nm (Figure 8-4 on page 8-8) is similar to
f
a
Q
x
Q
c
------ =
"Sun+Sky" 1.0 0.19
"Quartz Halogen" 1.11 0.26
"Fluorescent" 0.88 0.18
"Metal Halide" 0.87 0.17
"Neon Beer Sign" 0.70 .2_
/User/Configs/LightSources
Figure 18-23. Each entry in the list source list needs a quoted name, an actinity cor-
rection factor, and a conversion factor (used only for energy balance computations).
Light source name
(in quotes)
Correction factor (
f
a
)
Conversion factor for energy
balance computations