39
Some PAR Clips offer the option of using a predetermined light intensity level from an
internal fluorometer light source to measure Yield and ETR. In this case, irradiation levels
can be forced to be consistent for each sample. Note: When using internal illumination it is
important to allow time for a plant to reach steady state photosynthesis before measurement
or errors will result. Even small changes in irradiance level can change the measurement of
both yield and ETR. Maxwell and Johnson (2000) found that it takes between 15 minutes and
20 minutes for plants to reach steady state. (For more information on this topic see Opti-
Sciences App note # 0509, “Yield value & Limitations”.)
Some PAR Clips, such as the digital PAR clip for Opti-Sciences OS1p, allow PAR
measurement while an internal light source is being used, thus providing a reliable PAR or
PPFD values over time. Of course in this case, the PAR sensor should be calibrated to the
internal actinic illumination as well as to sun light. It should also be calibrated for the location
difference between the PAR sensor and the leaf sample (Rascher 2000).
To Next Page
Loading...
