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Low Light Measurements
Accurate low light measurements are required in flowering and light pollution studies. Research indicates
flowering can be triggered in some plants at photosynthetic and/or far-red photon flux densities less than 0.1 mol
-2
-1
m
s
. The threshold photon flux density at which flowering is triggered is variable among species. Two of the
most light-sensitive species are Poinsettias and Cannabis. For reference, photon flux density of moonlight when
the moon is full and near the minimum zenith angle is 0.005 mol m
-2
-1
s
.
The model SQ-620 Extended Range Quantum Sensor can measure a photon flux density range of 0-4000 mol m
-2
-1
s
. The model SQ-640 Quantum Light Pollution Sensor is designed for low light measurements and can only
measure a photon flux density range of 0-200 mol m
(the sensor will output values beyond, 200 mol m
-2
-1
-2
-1
s
s
,
but these are beyond the linear range of the sensor) and is referred to as the low light version. The sensitivity of
the SQ-640 is twenty times higher than the sensitivity of the SQ-620 (1 mV per mol m
-2
-1
s
versus 0.05 mV per
mol m
-2
-1
s
) to provide greater measurement resolution under low light conditions. For example, if the photon
flux density were 0.1 mol m
-2
-1
s
, the SQ-640 would output 0.1 mV, whereas the SQ-620 would output 0.005 mV.