USB QUANTUM SENSOR

Model JSQ-420

Internal Data Storage
The sensor has internal data storage capability with the ability tohold up to 10,000 measurements. This allows the sensor tocollect data while connected to a stand-alone 5 V DC power
supply such as an independent battery pack or USB wall adapter.

Application
The JSQ-420 is used to measureincoming and reflected PPFD aroundplants and other organisms in outdoor
environments, greenhouses, growthchambers, and underwater.

No Datalogger Required
The sensor can be connected to a desktop, laptop, or tablet
computer via USB 2.0 type A plug to be used with the software.
The included Apogee software gives the user control of data
logging and calibration settings, provides a real time output
display and graph of PPFD measurements and allows the data
set to be saved as a csv file.
Independent Calibration
The JSQ-420 is calibrated independently for sunlight and electric
light to improve measurement accuracy. The light source calibration
can be selected in the settings menu of the Apogee software.

SPECIFICATIONS•Resolution: 0.1 μmol m-2 s-1•Calibration Factor: custom for each sensor and stored in the firmware•Calibration Uncertainty: ± 5 % (see Calibration Traceability below)•Measurement Repeatability: less than 1 %•Non-stability (Long-term Drift): less than 2 % per year
•Non-linearity: less than 1 % (up to 3000 μmol m-2 s-1)
•Response Time: software updates every second•Field of View: 180o
•Spectral Range: 410 nm to 655 nm(wavelengths where response is greater than 50 % of maximum;
see Spectral Response below)•Directional (Cosine) Response: ± 5 % at 75o zenith angle(see Cosine Response below)•Temperature Response: 0.06 ± 0.06 % per °C(see Temperature Response below)•Operating Environment: -40~70°C, 0~100%RH(Can be submerged in water up to depths of 30 m)•Dimensions: 2.4 cm diameter and 2.8 cm height•Mass: Sensor head weighs 90 g
•USB Cable: 4.6 m (15 ft)•Current Draw (when Logging): 0.35 mA

7Spectral Response:

Mean spectral response of six sensors(error bars represent two standard
deviations above and below mean)
compared to PAR (PPFD) weighting
function. Spectral response
measurements were made at 10 nm
increments across a wavelength
range of 300 to 800 nm in a
monochromator with an attachedelectric light source. Measured
spectral data from each quantum
sensor were normalized by themeasured spectral response of themonochromator/electric lightcombination, which was measured
with a spectroradiometer.

Temperature response:

Mean temperature response of eight
replicate sensors (errors bars
represent two standard deviations
above and below mean).
Temperature response measurements
were made at 10 C intervals across atemperature range of -10 to 40 C ina temperature controlled chamber
under a fixed, broad spectrum,electric lamp. At each temperature
set point, a spectroradiometer wasused to measure light intensity fromthe lamp and all quantum sensors
were compared to thespectroradiometer. The
spectroradiometer was mounted
external to the temperature control
chamber and remained at room
temperature during themeasurements.

8Cosine Response:

Directional, or cosine, response
is defined as the measurement
error at a specific angle ofradiation incidence. Error for
Apogee SQ series quantum
sensors is approximately ± 2 %and ± 5 % at solar zenith anglesof 45° and 75°, respectively.

Mean cosine response oftwenty-three replicate sensors(error bars represent twostandard deviations above andbelow mean). Cosine response
measurements were made bydirect side-by-side comparison
to the mean of four reference
thermopile pyranometers, withsolar zenith angle-dependent
factors applied to convert total
shortwave radiation to PPFD.
Blue points represent the AM
response and red points
represent the PM response.

9DEPLOYMENT AND INSTALLATION
Mount the sensor to a solid surface with the nylon mounting screw provided. To accurately
measure PPFD incident on a horizontal surface, the sensor must be level. An Apogee Instruments
model AL-100 leveling plate is recommended for this purpose. To facilitate mounting on a crossarm, an Apogee Instruments model AM-110 mounting bracket is recommended.

To minimize azimuth error, the sensor should bemounted with the cable pointing toward true northin the northern hemisphere or true south in thesouthern hemisphere. Azimuth error is typically lessthan 1 %, but it is easy to minimize by proper cableorientation.

In addition to orienting the cable to point toward the nearest pole, the sensor should also be
mounted such that obstructions (e.g., weather station tripod/tower or other instrumentation) do
not shade the sensor. Once mounted, the green cap should be removed from the sensor. The
green cap can be used as a protective covering for the sensor when it is not in use.

11

OPERATION AND MEASUREMENT
Spectral Errors and Yield Photon Flux Measurements:
Apogee quantum sensors are calibrated to measure PPFD for either sunlight or electric light. The
difference between the calibrations is 14 %. A sensor calibrated for electric lights (calibration
source is T5 cool white fluorescent lamps) will read approximately 14 % low in sunlight.
In addition to PPFD measurements, Apogee SQ series quantum sensors can also be used tomeasure yield photon flux density (YPFD): photon flux weighted according to the plant
photosynthetic action spectrum (McCree, 1972) and summed. YPFD is also expressed in units ofmol m-2 s-1, and is similar to PPFD, but is typically more closely correlated to photosynthesis thanPPFD. PPFD is usually measured and reported because the PPFD spectral weighting function(equal weight given to all photons between 400 and 700 nm; no weight given to photons
outside this range) is easier to define and measure, and as a result, PPFD is widely accepted. Thecalibration factor for YPFD is 10 % lower than the calibration factor for PPFD.
The weighting functions for PPFD and YPFD are shown in the graph below, along with thespectral response of Apogee SQ series quantum sensors. The closer the spectral response
matches the defined PPFD or YPFD spectral weighting functions, the smaller spectral errors will
be. The table below provides spectral error estimates for PPFD and YPFD measurements fromlight sources different than the calibration source. The method of Federer and Tanner (1966) wasused to determine spectral errors based on the PPFD and YPFD spectral weighting functions,
measured sensor spectral response, and radiation source spectral outputs (measured with aspectroradiometer). This method calculates spectral error and does not consider calibration,cosine, and temperature errors.
Federer, C. A., and C. B. Tanner, 1966. Sensors for measuring light available for photosynthesis.
Ecology 47:654-657.
McCree, K. J., 1972. The action spectrum, absorptance and quantum yield of photosynthesis incrop plants. Agricultural Meteorology 9:191-216.

Radiation weighting factors for
PPFD (defined plant responseto radiation), YPFD (measuredplant response to radiation),and Apogee SQ Series
quantum sensors (sensorsensitivity to different
wavelengths of radiation).