CHAPTER 7
15
TERMINOLOGY
PPFD: Photosynthetic Photon Flux Density.
The term photon flux density is often used equivalent to photon ir-
radiance (see above for exact definition, compare Björn 2008).
The photosynthetic photon flux density is restricted to the range
of wavebands between 400 and 700 nm. Unit: µmol m
-2
s
-1
.
PPFD is measured with cosine corrected sensors having a plane
surface (e.g. the Micro quantum sensor MQS).
PPFR: Photosynthetic Photon Fluence Rate.
The photon fluence rate is defined as total number of photons in-
cident per time interval from all directions on a small sphere divided
by the cross-sectional area of the sphere (Braslavsky, 2007). It has
also been called photon spherical irradiance, scalar irradiance or pho-
ton flux fluence rate.
The photosynthetic photon fluence rate is restricted to the range of
wavebands between 400 and 700 nm. Unit: µmol m
-2
s
-1
PPFR is measured with spherical sensors.
