System Setup and Operation
CIRAS-2 Operator's Manual Version 2.04
- 45 -
Light Type
In the
„Light Type‟ list select from correct Light Unit (or light source) used with your cuvette (Ambient, LED
or Tungsten Halogen). Available options are based on Probe Type and Chamber/Cuvette Type selected.
Leaf Temperature (T
leaf
)
Depending on cuvette/chamber selection - IR Sensor/Energy Balance/Thermistor. The IR sensor is only
available with modern PLC6 (U) and PLC5 (B) Automatic Leaf Cuvettes. Energy Balance is provided as
secondary choice.
Leaf Temperature Determination: Explanations
Accurate measurement of leaf temperature (T
leaf
) is essential for the determination of stomatal
conductance. In determining the water vapor pressure gradient between the leaf and the outside air (the
driving force for transpiration) the air inside the leaf is assumed to be saturated at the leaf temperature.
T
leaf
is determined by the balance between energy absorbed by the leaf from incident radiation (visible and
short wave infra-red), energy lost in the evaporation of water, energy either gained or lost in long wave
radiation to the surroundings and in conduction with the surrounding air. There are three commonly used
methods used to measure T
leaf
which CIRAS-2 makes available to the user depending on the type of
cuvette.
1. Energy Balance
2. Thermistor
3. Infrared sensor (IR)
Energy Balance
All “Manual” and “Automatic” type leaf cuvettes have this option available, and we recommend this in
preference to the “Thermistor” method described below. This method of T
leaf
measurement produces a
reasonably good average for T
leaf
. As mentioned above, the energy balance of the leaf determines the
temperature, so the more accurately we determine these components the better we can calculate the
temperature.
