Hybride irradiation as best available practice in artificial plant lighting

Abstract

Growing of plants in artificial lighting conditions require a certain irradiation spectrum. High-pressure sodium (HPS) lamps are the cheapest way to generate optical radiation. However, their light quality is not fully suitable for plants. Light-emitting diodes (LEDs) allow for almost any light quality, but they are still more expensive than HPS lamps. The study objective was to identify the light quality of a LED spectrum corrector used to complement HPS lamps in artificial plant lighting and to prove the practical relevance of this solution in the laboratory and commercial greenhouse conditions. A comparative laboratory experiment was carried out on tomato (Solanum Lycopersicum L.) transplants, Blagovest F1 cultivar, in IEEP (Saint Petersburg, Russia). The use of the spectrum corrector improved the transplants biometrics: increased number of leaves and their fresh mass, higher chlorophyll and dry matter content. A greenhouse experiment was carried out in Mezhvidi (Latgalia, Latvia) on mature tomato plants of Encore cultivar in three variants: under HPS lamps, under Phillips LED irradiators, and under the irradiators combining HPS lamps and the spectrum corrector. The effect of the irradiator type on the plants was assessed by the plant developmental stability estimated by the fluctuating asymmetry (FA) of the leaf bilateral traits. The least favourable light environment with the maximum fluctuating asymmetry was found under HPS lamps (FA avg = 0.1064 rel. units). LED irradiators created better conditions for plant development (FA avg = 0.0767 rel. units). The use of the spectrum corrector provided the best light environment (FA av = 0.0659 rel. units). Under the combined irradiation, a higher yield and improved taste of tomato fruits were recorded. The experiment results prove the hybrid irradiation to improve the artificial plant lighting efficiency.