In Fig. 3 the Hue readings are plotted as a function of time
. The yellowing tendency can be approximated to an exponential decay
behavior according to a generic function Y=Ae?(x/t), where t
indicates the temporal factor i.e., the rate (x/t) expresses the speed
of the decay. All curves present R2 > 0.9 indicating the goodness-of fit
for all conditions, allowing some interesting conclusions to be
drawn.