Articles
Optimised light use efficiency in greenhouse lettuce production with a combined approach of optimised cultivation area, light intensity and light quality
Article number
1423_21
Pages
155 – 162
Language
English
Abstract
In greenhouse production above a certain latitude supplementary lighting is inevitable for high quality and yield of vegetable production such as lettuce.
To maximise the light use efficiency in terms of consumed electricity, we have tested a three-step approach on two head-lettuce cultivars ‘Alyssa’ and ‘Coconino’, combining 1) optimised cultivation area throughout the 4-week production with a movable gutter system, 2) dynamic supplementary lighting with automised adjustable supplementary light intensity, and 3) selected spectral composition of red and blue LEDs optimising light use efficiency in terms of energy consumption and photosynthesis.
The first two factors were tested in an experimental approach in a nine line moving-gutter-system (MGS) equipped with automated irrigation over a 12-week period between September and November 2023. In this experiment we applied three minimum light levels of 100, 200 and 300 µmol m‑2 s‑1 with white LED lamps for a daily light period of 16 h in three replications in space and three full replications in time.
During the production various physical measurements were done at the non-destructive monitoring level of optical thermography, microclimate (temperature, humidity, CO2, spectral light), leaf photosynthesis, chlorophyll fluorescence, and stomatal conductance as well as weekly destructive measurements on fresh and dry yield, leaf number and leaf area.
The data were used feeding a simulation model.
A scenario simulation using the climate and light-switch data from the experiment achieved during the 12-week period on light quality was done.
The simulations were performed with three levels of red and blue light mixes with the same supplementary total light amount as in the experiment with 100, 200 and 300 µmol m‑2 s‑1. Compared to regular plant spacing the light use efficiency could be strongly improved and as well as with the automated light level adjustments compared to a fixed level.
A higher light-use efficiency was observed when selecting LEDs on the spectral composition of red and blue.
Future investigation will focus on optimising dynamic light levels for each cultivation stage.
To maximise the light use efficiency in terms of consumed electricity, we have tested a three-step approach on two head-lettuce cultivars ‘Alyssa’ and ‘Coconino’, combining 1) optimised cultivation area throughout the 4-week production with a movable gutter system, 2) dynamic supplementary lighting with automised adjustable supplementary light intensity, and 3) selected spectral composition of red and blue LEDs optimising light use efficiency in terms of energy consumption and photosynthesis.
The first two factors were tested in an experimental approach in a nine line moving-gutter-system (MGS) equipped with automated irrigation over a 12-week period between September and November 2023. In this experiment we applied three minimum light levels of 100, 200 and 300 µmol m‑2 s‑1 with white LED lamps for a daily light period of 16 h in three replications in space and three full replications in time.
During the production various physical measurements were done at the non-destructive monitoring level of optical thermography, microclimate (temperature, humidity, CO2, spectral light), leaf photosynthesis, chlorophyll fluorescence, and stomatal conductance as well as weekly destructive measurements on fresh and dry yield, leaf number and leaf area.
The data were used feeding a simulation model.
A scenario simulation using the climate and light-switch data from the experiment achieved during the 12-week period on light quality was done.
The simulations were performed with three levels of red and blue light mixes with the same supplementary total light amount as in the experiment with 100, 200 and 300 µmol m‑2 s‑1. Compared to regular plant spacing the light use efficiency could be strongly improved and as well as with the automated light level adjustments compared to a fixed level.
A higher light-use efficiency was observed when selecting LEDs on the spectral composition of red and blue.
Future investigation will focus on optimising dynamic light levels for each cultivation stage.
Authors
A. Pannico, N. Arouna, S. Pinho, A. Filipenko, G.C. Modarelli, S. De Pascale, O. Körner
Keywords
lettuce, dynamic light control, LED, red light, blue light, energy use efficiency
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