Using chlorophyll a fluorescence gains to optimize LED light spectrum for short term photosynthesis

Relation between Changes in Photosynthetic Rate and Changes in Canopy Level Chlorophyll Fluorescence Generated by Light Excitation of Different Led Colours in Various Background Light

“…Earlier work did not show satisfactory results when analysing reflected light, and therefore we have focused on analysing the data in the fluorescence band (having a first peak at 685 nm and a second at 740 nm). Furthermore, previous research [16] found a better correlation between photosynthetic rate and the fluorescence at 740 nm, compared to the peak at 685 nm. In addition, LED 660 significantly overlaps with the fluorescence spectrum at 685 nm though it was assumed not to overlap at 740 nm at the time of the experiments (later it was, however, found to have a small overlap affecting the results to some extent, see Section 3.2.3).…”

“…However, the absolute quantities of both fluorescence and photosynthesis are expected to increase with an increased incident light intensity, and the absolute values (not to be confused with the fraction) will hence be positively correlated. We have seen that there is indeed a strong correlation between steady-state chlorophyll a fluorescence at 740 nm (F740) and photosynthetic rate (measurements on basil, in absence of background light, [16]), which indicates that the F740 could be a useful remotely measured signal to estimate the photosynthetic efficiency. The maximum photosynthetic rate for a predefined total power corresponds to the spectrum that maximies F740 [10].…”

“…However, red LEDs caused the highest fluorescence gains per incident quanta for all species tested. Experiments on basil have also been conducted under various background light [16]. In contrast to the working hypothesis, that the mutual relations of the fluorescence gains would vary with various background light, the variation of individual fluorescence gains were minor for the background lights studied.…”

“…We define the steady-state chlorophyll a fluorescence gain (dF740/dq) as the difference in fluorescence at 740 nm divided by the difference in incident light quanta caused by (a small) excitation of one LED colour. This work is an expansion of earlier research [16,17], where we proposed the use of the fluorescence gain as an measure of the photosynthetic efficiency increase, to be used as a feedback signal in a (future) self-optimising controller to find the optimal light spectrum.…”

Light spectrum optimization for plant growth using biological feedback

“…A potential candidate signal is steady-state chlorophyll a fluorescence gain at 740 nm, defined as dF740/dq, i.e. the difference in fluorescence at 740 nm divided by the difference in incident light quanta caused by a (small) change in intensity of each individual LED color in the lamp (Ahlman et al, 2017). By automatically adjusting the spectrum, to aim for equal fluorescence gains for all LED colors (Wik et al, 2014), the instant photosynthetic rate can be optimised given a preset electric power input to the lamp.…”