User Manual
Spectral Errors for PPFD and YPFD Measurements with Apogee SQ Series Quantum Sensors
Radiation Source (Error Calculated Relative to Sun, Clear Sky)
SQ-100 Series
PPFD Error [%]
SQ-500 Series
PPFD Error [%]
Sun (Clear Sky)
0.0
0.0
Sun (Cloudy Sky)
1.4
0.5
Reflected from Grass Canopy
5.7
0.0
Transmitted below Wheat Canopy
6.4
1.1
Cool White Fluorescent (T5)
0.0
2.2
Metal Halide
-3.7
3.1
Ceramic Metal Halide
-6.0
1.9
High Pressure Sodium
0.8
2.2
Blue LED (448 nm peak, 20 nm full-width half-maximum)
-12.7
3.0
Green LED (524 nm peak, 30 nm full-width half-maximum)
8.0
5.2
Red LED (635 nm peak, 20 nm full-width half-maximum)
4.8
0.2
Red LED (668 nm peak, 20 nm full-width half-maximum)
-79.1
-1.9
Red, Blue LED Mixture (84 % Red, 16 % Blue)
-65.3
-1.2
Red, White LED Mixture (79 % Red, 21 % Blue)
-60.3
-0.8
Quantum sensors can be a very practical means of measuring PPFD and YPFD from multiple radiation sources, but
spectral errors must be considered. The spectral errors in the table above can be used as correction factors for
individual radiation sources.
Federer, C.A., and C.B. Tanner, 1966. Sensors for measuring light available for photosynthesis. Ecology 47:654-657.
Ross, J., and M. Sulev, 2000. Sources of errors in measurements of PAR. Agricultural and Forest Meteorology
100:103-125.
Yield Photon Flux Measurements
Photosynthesis in plants does not respond equally to all photons. Relative quantum yield (photosynthetic
efficiency) is dependent on wavelength (blue line in figure below) (McCree, 1972a; Inada, 1976). This is due to the
combination of spectral absorptivity of plant leaves (absorptivity is higher for blue and red photons than green
photons) and absorption by non-photosynthetic pigments. As a result, photons in the wavelength range of
approximately 600-630 nm are the most efficient.
Radiation weighting factors for
PPFD (black line, defined plant
response to radiation), YPFD
(blue line, measured plant
response to radiation), and
Apogee SQ-500 Series Quantum
Sensors (green line, sensor
sensitivity to different
wavelengths of radiation).