An ideal quantum sensor would give equal emphasis to all photons
between 400 and
700 nm and would exclude photons above and
below these wavelengths. The response of such a sensor is
shown in the adjacent graph. The most accurate way to
measure this radiation is with our
spectroradiometer, which
costs less than $4000. Our quantum meters are accurate to
within about ±3 % for common light sources.
The spectral response of the Apogee Sensor used in Quantum
Meters and the Quantum Sensor is shown at right. As the
figure indicates, the sensor underestimates the 400 to 500
nm wavelengths (blue light), overestimates the 550-650
wavelengths (yellow and orange light), and has little
sensitivity above 650 nm (red light). Fortunately, common
light sources are mixtures of colors and the spectral errors
offset each other. The sensor measures green light (500-550
nm) accurately, so it can be used to measure the radiation
inside and at the bottom of plant canopies.
The graph below shows the two spectral responses of our
Dual
Radiation Meter. The green line is the unfiltered quantum
sensor photodiode that measures Photosynthetic Photon Flux (PPF)
and the blue line is the Human Eye Response typically
measured in Footcandles.
SENSOR RESPONSE
