Indoor living green walls of aromatic plants lit with LEDs

M. Dorais, A. Brégard, C. Ménard, B. Dansereau, N. Zyromski, S. Pepin
The LED technology for indoor lighting is promising because LEDs have a good energy use efficiency, wide range of specific wavelengths, durability, cool emitting temperature and small size. In addition to providing photosynthetic light, the spectral quality of LED light may influence plant morphology, enhance the production of bioactive health compounds, control pests and diseases and create an interesting lighting ambiance and design which can be timely modulated. Thus, LED lighting may overcome the most important limiting growing factor of indoor living green walls which is the amount of available photosynthetic light to support plant growth. Our hypothesis was that LED lamps are good tools for lighting indoor vertical green walls containing various edible aromatic plants. The objective of the present study was to evaluate the performance of different LED lighting regimes for green wall plants grown under low PPFD, normally observed inside a building. Plant growth and phenolic metabolites content were evaluated on eight species of herbs (Mentha citrata, Mentha piperita, Mentha spicata, Origanum vulgare, Rosmarinus officinalis, Salvia officinalis, Stevia rebodiana, Thymus vulgaris) when using six LED light treatments obtained by combining three sets of LEDs with two intensities (100 and 50%). The three sets of LEDs were white (W; 0.12B:0.18G:0.71R), blue:red (BR; 0.09B:0.91R) and blue:red + far-red (BRFR; 0.05B:0.52R:0.42FR) with different wavelength peaks of 447 and 660 nm (W), 465 and 660 nm (BR), and 465, 660 and 730 nm (BRFR). At 100% intensity, the PPFD were 91 µmol m‑2 s‑1 (W), 94 µmol m‑2 s‑1 (BR) and 100 µmol m-2 s-1 (BRFR) for a 12-h photoperiod. Dimensions of vertical green wall plastic modules were 100 cm (H) × 50 cm (W) × 7.5 cm (D) filled with rockwool slab in which the herb plugs were planted three weeks prior to the beginning of the experiment. The experiment was a randomized complete design replicated twice with three modules per replicate. Our results showed that indoor green walls of aromatic plants can advantageously be lit by LEDs. The use of BR LEDs and BRFR LEDs resulted in lower chlorophyll leaf content compared with W LEDs, but plants had greatest activities of photosystem II and greatest concentrations of phenolics with no significant effect on the plant biomass. Higher PPFD did not yield better in terms of plant biomass than 50% lower PPFD.
Dorais, M., Brégard, A., Ménard, C., Dansereau, B., Zyromski, N. and Pepin, S. (2020). Indoor living green walls of aromatic plants lit with LEDs. Acta Hortic. 1287, 117-126
DOI: 10.17660/ActaHortic.2020.1287.16
herbs, living wall, phenolics, supplemental lighting, vertical farming

Acta Horticulturae