Outdoor light intensity measurement
The light intensity
was measured every 6 minutes by a brightness
transmitter 7.1414.51.150 from Thies Clima (Göttingen,
Germany). The light intensity was measured in lux and
was converted to PAR (µmol PAR.m
−2
.s
−1
) by dividing
lux by 82. This correction factor was determined by comparing
the values of simultaneously measured lux and PAR
at the Montrigi weather station (Belgium).