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Light sources
There are multiple standard light sources present in the OS1p:
Modulated light source
This is the light source that makes light adapted quantum
photosynthetic yield measurements possible along with direct measurements of Fo and Fo’ or
Fod. The modulated light source is used at an intensity range that is too low to drive
photosynthesis and yet allows fluorescence measurement of pre-photosynthesis Fo, and post
photosynthesis Fo’ or Fod. This light source is turned off and on at a particular frequency.
Opti-Sciences adjusts the frequency automatically.
1.
The standard modulation source is a 660nm output used exclusively for measuring of
the fluorescence signal. It's intensity may be varied to adjust for dark adapted samples
and for use with the PAR clip on light adapted samples.
Optional:
2.
The second modulation source is a 450nm LED and is also used exclusively for
measuring of the fluorescence signal. The red source can be replaced by a blue source
at time of order. It's intensity may be varied to adjust for dark clips, Par Clips, and
sample differences as well. Because of absorption differences, using the blue
modulated light source will change ETR values. In the equation used for blue
modulated light, leaf absorption should be changed to 0.94, on average, from 0.84. for
best correlation to red modulated light values. This can be done in Excel using the
measuring file. ETR= Yield X PAR X 0.94 X 0.5 (for blue modulated light).
Saturation pulse light source
is a short pulse of intense light designed to fully reduce a
leaf’s PSII system. For higher plants, the optimal duration of the saturation pulse is between
0.5 seconds and 1.5 seconds (Rosenqvist and van Kooten 2006). For Algae and cynobacteria,
the duration must be shorter to provide accurate measurements 0.025 to 0.050 seconds.
(Schreiber 1995). Opti-Sciences uses 0.8 seconds as the default value for land plants however
the duration can be set between 0.1 seconds and 2.0 seconds by pressing the Y(II) graph on
the Y(II) measuring screen and pressing the duration button. The Saturation pulse light source
is a high intensity white light LED. The Saturation light source is 11,000
:
mols at 100%
intensity when used with a dark clip, and about 6600
:
mols when used with the PAR Clip at
100% intensity. The machine actually measures 320 points in one second, and gives the
highest eight point rolling average as an Fm’ measurement value.
Algae and cyanobacteria saturation pulse duration - new feature:
The ideal saturation pulse duration for algae and cyanobacteria range from 0.025 seconds and
0.050 seconds (Schreiber 1995). When using the OS1p for algae work, the OS1p uses a
special algorithm that finds the highest eight point rolling average at the top of the saturation
pulse. The eight point average represents a time of 25ms. Therefore, finding the optimal
saturation duration is always achieved for algae without testing. With a saturation pulse
