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Industrial greenhouses are integrating various Internet of Things (IoT) based sensor technologies to create cloud-based database solutions. Industrial greenhouse control systems are no exception in this regard, as they have recently become more and more popular with the use of various sensors including different types of weight sensors for automation of vegetable and other crop cultivation processes. One of the most important factors hindering the wider implementation of weighting systems in the greenhouse is their high price, where the largest costs are related to the weighing sensors themselves. In addition to the price factor, weight sensor systems on the market are often characterized by known structural and functional limitations, which can be solved if developing a new weighting system. The authors have created and installed IoT based weight sensor modules (TWS) to monitor different weight changes in time, such as irrigation cycle amount or daily tomato yield/weight increase values in real tomato greenhouse of "Latgales darzenu logistika" (further LDL) in Mezvidi parish, with a total growing area of 5062.4 m 2 . This article reveals the test results that are related to measurement stability in 3-year period, measuring the weight parameters 24/7. As a reference, a constant weight was attached to one sensor all the time, and all of them were affected by the industrial greenhouse environment (temperature, humidity, etc). Furthermore, TWS readings were analysed and compared to real greenhouse crop yield data during the growing season (10 months) in weekly periods, allowing to asses potential application of TWS for automatic crop yield evaluation and this data usage for greenhouse control systems or their control algorithm correction issues, with the general aim to raise the level of process automation, quality, energy efficiency, and other important parameters.

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.

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