Pulsed light − optimal ratio between yield and energy reduction

S. Wittmann, I. Jüttner, H. Mempel
In the future indoor vertical farming will become a year-round supplier of high-quality raw plant materials and an important addition to conventional cultivation methods. However, there are still challenges to establish indoor vertical farming as a profitable system, as the investment and running costs are particularly high. Pulse width modulation (PWM) was mentioned in several studies to have a high potential to increase the light energy use efficiency (EUE − plant biomass produced per unit of energy supplied). One approach is the preservation of plant growth at similar values compared to continuous lighting with fewer energy supply and therefore lower light intensities on the irradiated area. The aim of this work was to determine the plant biomass and growth of basil (Ocimum basilicum L. ‘Genovese’) as one popular plant grown in indoor vertical farming under reduced duty cycles (and therefore lower light intensities) and two low frequencies in comparison to continuous light, also considering the EUE. Plants were grown in two subsequent trials for 19 days after germination under a white LED spectra at 75, 85 and 100% (200±23 µmol m‑2 s‑1) duty cycle and two different frequencies (50 Hz, 120 Hz). Accordingly, a DLI of 15 mol m‑2 d‑1 (100%), 13 mol m‑2 d‑1 (85%) and 11 mol m‑2 d‑1 (75%) was reached. A duty cycle of 
85% showed a reduction in the energy supply of 25% without growth inhibition. The assimilation rate was not influenced by the applied duty cycles. An annual yield of 68±5.4 kg m‑2 was reached. Nevertheless, there was no positive effect on the EUE.
Wittmann, S., Jüttner, I. and Mempel, H. (2023). Pulsed light − optimal ratio between yield and energy reduction. Acta Hortic. 1369, 227-234
DOI: 10.17660/ActaHortic.2023.1369.28
electrical energy efficiency, indoor farming, pulse width modulation

Acta Horticulturae