Apogee Instruments MQ-620 Benutzerhandbuch - Seite 4
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Radiation that drives photosynthesis is called photosynthetically active radiation (PAR) and is typically defined as
total radiation across a range of 400 to 700 nm. PAR is almost universally quantified as photosynthetic photon flux
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density (PPFD) in units of micromoles per square meter per second (µmol m
s
, equal to microEinsteins per
square meter per second) summed from 400 to 700 nm (total number of photons from 400 to 700 nm). However,
ultraviolet and far red photons outside the defined PAR range of 400-700 nm can also contribute to photosynthesis
and influence plant responses (e.g., flowering).
Sensors that measure PPFD are often called quantum sensors due to the quantized nature of radiation. A quantum
refers to the minimum quantity of radiation, one photon, involved in physical interactions (e.g., absorption by
photosynthetic pigments). In other words, one photon is a single quantum of radiation. Sensors that function like
traditional quantum sensors, but measure a wider range of wavelengths can be thought of as an 'extended range'
quantum sensor.
Typical applications of traditional quantum sensors include incoming PPFD measurement over plant canopies in
outdoor environments or in greenhouses and growth chambers, and reflected or under-canopy (transmitted) PPFD
measurement in the same environments. The Extended Range PFD Sensor detailed in this manual uses a detector
that is sensitive to radiation up to about 1100 nm, well beyond the range of wavelengths that influence
photosynthesis and plant responses. This means this particular sensor should only be used for photon flux
density measurements under LEDs.
Apogee Instruments MQ-620 meters consist of a handheld meter and a dedicated sensor that is connected by
cable to an anodized aluminum housing. SQ-600 series Extended Range PFD Sensors consist of a cast acrylic
diffuser (filter), photodiode, signal processing circuitry mounted in an anodized aluminum housing, and are potted
solid with no internal air space. MQ series extended range PFD meters provide a real-time PFD reading on the LCD
display, that determine the radiation incident on a planar surface (does not have to be horizontal), where the
radiation emanates from all angles of a hemisphere. MQ series quantum meters include manual and automatic
data logging features for making spot-check measurements.