3
A quantum is the amount of energy possessed by a photon.
Photosynthesis is driven primarily by light in the range be-
tween 400 and 700 nanometers, which is referred to as Photo-
synthetically Active Radiation, or PAR light. The intensity of
PAR light is referred to as Photosynthetic Photon Flux Den-
sity (PPFD), which is measured in units of µmol m
-2
s
-1
(the
number of photons in units of micromoles, striking an area
one meter square each second). Quantum Light Meters are
calibrated to display PPFD. The meters display PPFD in the
range 0-1999 µmol m
-2
s
-1
.
Field Scout Quantum Light Meters are calibrated for sunlight.
Due to differences in the spectrum generated by artificial
lights, the following adjustments must be made in the value
shown on a sunlight-calibrated meter:
Fluorescent: reads 8% high, so multiply the display by 0.92.
Metal Halide: reads 6% high, so multiply the display by 0.94.
High Pressure Sodium: 0% error—no adjustment needed.
Sunlight: 0% error—no adjustment needed.
Note that the 3415FSE meter displays accurate readings for
fluorescent lights when set to “Electric”.
The chart below displays the spectral response of the Quan-
tum Light Meters.