Supplemental Lighting Intensity Research Articles

Intelligent control and energy optimization in controlled environment agriculture via nonlinear model predictive control of semi-closed greenhouse

Greenhouse climate is a highly complex system that contains nonlinearity and dependencies between each system state. This paper proposes a novel nonlinear model predictive control (NMPC) framework for greenhouse climate control to minimize the total control cost mainly coming from energy use. A nonlinear dynamic model of the greenhouse climate, including temperature, humidity, CO2 level, and light intensity, is first constructed based on developed mass balances and energy transport phenomena. Real-world greenhouse climate data and outdoor weather data are gathered to systematically identify the system parameters for the nonlinear greenhouse climate model. The nonlinear dynamic model is then integrated into the proposed NMPC framework which iteratively solves a nonlinear programming problem to obtain the optimal control inputs of fan airflow rate, pad cooling air velocity, heating pipe flow rate, CO2 injection rate, fogging rate, supplemental light intensity, and shade curtain coverage. The stability and feasibility issues of the proposed NMPC framework on a semi-closed greenhouse are explicitly discussed in this work. Case studies on controlling a greenhouse located in Cornell University campus are simulated to demonstrate the performance of the proposed NMPC framework. The results show the NMPC framework could efficiently minimize total control cost and constraint violation. Humidity, CO2 level, and light intensity can be controlled with nearly no violation on the predetermined constraints over different seasons and climate conditions. As for temperature, it is almost always maintained within the acceptable region in winter and spring. On extreme days of summer, there are some temperature violations due to the limited cooling capacity.

Increasing Levels of Supplemental LED Light Enhances the Rate Flower Development of Greenhouse-grown Cut Gerbera but does not Affect Flower Size and Quality

To investigate the influence of supplemental lighting intensity on the production (i.e., rate of flower development, flower quality, and yield) of cut gerbera during Canada’s supplemental lighting season (November to March), trials were carried out at a research greenhouse. Five supplemental light emitting diode (LED) light intensity (LI) treatments provided canopy-level photosynthetic photon flux densities (PPFD) ranging from 41 to 180 µmol m−2 s−1. With a 12-h photoperiod, the treatments provided 1.76 to 7.72 mol m−2 d−1 of supplemental light. Two cultivars of cut gerbera (Gerbera jamesonii H. Bolus ex Hook.f) were used to evaluate vegetative growth and flower production. Plugs of ‘Ultima’ were assessed for vegetative growth and rate of flower development. There were minor LI treatment effects on number of leaves and chlorophyll content index and flowers from plants under the highest versus the lowest LI matured 10% faster. Reproductively mature ‘Panama’ plants were assessed for flower yield and quality. ‘Panama’ flowers from the highest LI treatment had shorter stems than the three lowest LI treatments, and flowers from the middle LI treatment had larger diameter than the other treatments. Flowers from the lowest LI treatment had lower fresh mass than the three highest LI treatments. There were linear relationships between LI and numbers of flowers harvested, with the highest LI treatment producing 10.3 and 7.0 more total and marketable flowers per plant than the lowest LI treatment. In general, increasing levels of supplemental light had only minor effects on vegetative growth (young plants) and size and quality of harvested flowers (mature plants), but flowers from plants grown under higher LIs were more numerous and matured faster.

A photochemistry-based method for optimising greenhouse supplemental light intensity

Supplemental lighting in greenhouses can increase crop growth, improving rates of greenhouse production. The advent of light-emitting diodes (LEDs) for photosynthetic lighting presents new opportunities for optimising greenhouse supplemental lighting control. Because LED light intensity can be controlled rapidly and precisely in real time, these lights can be controlled such that supplemental light is provided when it will be most efficiently used to drive photosynthesis. This approach to supplemental lighting control has the potential to reduce the electricity cost associated with greenhouse lighting while retaining the beneficial effects on crop growth, thereby decreasing the financial cost and improving the sustainability of greenhouse crop production. In this paper, an optimisation problem is formulated to minimise the total amount of electricity used by supplemental LED lights, subject to achieving a specified daily amount of photochemistry. An algorithm to solve the problem explicitly based on sufficient conditions for a global minimiser is developed. This method represents a computationally simple and broadly applicable means for minimising the amount of electricity required for supplemental lighting in greenhouses.

Light-emitting Diodes Can Replace High-pressure Sodium Lighting for Cut Gerbera Production

A greenhouse study was undertaken to investigate whether light-emitting diode (LED) technology can be used to replace high-pressure sodium (HPS) lighting for cut gerbera production during Canada’s traditional supplemental lighting (SL) season (November to March). The study was carried out at the University of Guelph’s research greenhouse, using concurrent replications of SL treatments within the same growing environment. LED (85% red, 15% blue) and HPS treatment plots were set up to provide equal amounts of supplemental photosynthetically active radiation (PAR) at bench level. This setup was used to assess the production of three cultivars of cut gerbera (Gerbera jamesonii H. Bolus ex Hook.f): Acapulco, Heatwave, and Terra Saffier. There were no treatment differences in SL intensity, with average SL photosynthetic photon flux density (PPFD) and daily light integral (DLI) of 55.9 µmol·m−2·s−1 and 2.3 mol·m−2·d−1, respectively. Flowers harvested from the LED treatment had a 1.9% larger flower diameter in ‘Acapulco’; 4.2% shorter and 3.8% longer stems in ‘Heatwave’ and ‘Terra Saffier’, respectively; and 7.7% and 8.6% higher fresh weights for ‘Acapulco’ and ‘Terra Saffier’, respectively, compared with flowers harvested from the HPS treatment. There were no differences in accumulated total or marketable flower harvests for any of the cultivars. The vase life of ‘Acapulco’ flowers grown under the LED treatment was 2.7 d longer than those grown under the HPS treatment, but there were no SL treatment effects on water uptake for any of the cultivars during the vase life trials. There were no SL treatment effects on specific leaf area for any of the cultivars. There were only minimal treatment differences in leaf, soil, and air temperatures. Cut gerbera crops grown with under LED SL had equivalent or better production and crop quality metrics compared with crops grown under HPS SL.

Supplemental blue light increases growth and quality of greenhouse pak choi depending on cultivar and supplemental light intensity

To evaluate the supplementary blue light intensity on growth and health-promoting compounds in pak choi (Brassica campestris ssp. chinensis var. communis), four blue light intensity treatments (T0, T50, T100 and T150 indicate 0, 50, 100, and 150 µmol m−2 s−1, respectively) were applied 10 days before harvest under greenhouse conditions. Both of cultivars (greenand red-leaf pak choi) under T50 had the highest yield, content of chlorophyll and sugars. With light intensity increasing, antioxidant compounds (vitamin C and carotenoids) significantly increased, while nitrate content showed an opposite trend. The health-promoting compounds (phenolics, flavonoids, anthocyanins, and glucosinolates) were significantly higher under supplementary light treatment than T0, so as the antioxidant capacity (2,2-diphenyl-1-picrylhydrazyl and ferric-reducing antioxidant power). The species-specific differences in photosynthetic pigment and health-promoting compounds was found in green- and red-leaf pak choi. T50 treatment could be used for yield improvement, whereas T100 treatment could be applied for quality improvement. Results showed that blue light intensity can regulate the accumulation of biomass, morphology and health-promoting compounds in pak choi under greenhouse conditions.

Design of Adaptive LED Supplemental Lighting System Based on LabVIEW

With the global increase in energy prices and the urgent need to reduce CO2 emissions to the atmosphere, high energy usage is the main problem the greenhouse industry facing. Optimized control of supplemental lighting intensity and quality help to improve productivity and energy efficiency of greenhouse.In this paper,LED light source module is developed according to the design of light distribution of RRGB chip based on plants need for uniform lighting. Adaptive LED supplementary lighting system realize collection, storage and call of environmental data, and adaptive regulation of red, green, and blue light output based on combination of upper computer LabVIEW and controller STM32.PC based on LabVIEW monitor environmental parameters,and call or choose PPFD setting value of red, green, blue three bands of light based on expert database. The controller communicating with LabVIEW wirelessly through WiFi module, conducts real-time detection and adaptive regulation on photosynthetic photon flux density (PPFD) of red, green and blue bands according to PPFD setting value. This intelligent supplemental lighting system meets the requirement of plants for lighting environment and greatly saving energies through adaptive adjustment of PPFD of red, green and blue bands in environment according to the setting based on different supplemental lighting demands of different plants or the same plant in different growth stages for PPFD and light quality ratio.

Shoot Growth and Flower Quality of Cut Rose ‘Pink Bell’ as Affected by Supplemental Lighting Intensity

Shoot Growth and Flower Quality of Cut Rose ‘Pink Bell’ as Affected by Supplemental Lighting Intensity

Dynamic control of supplemental lighting intensity in a greenhouse environment

The global increase in energy prices, the urgent need to reduce CO2 emissions to the atmosphere and the high energy usage are currently the major threats to the greenhouse industry. Optimised control of the lighting quality, quantity and periodicity can contribute to improvements in the productivity and energy efficiency of greenhouses. In this paper, the effects of dynamic control of supplemental lighting intensity on electricity consumption and fresh weight accumulation of lettuce plants are investigated. The use of the dynamic lighting control resulted in a 20% reduction in the electricity consumption in comparison to a similar lighting system operated under a discontinuous on–off regime. However, there was no statistically significant difference between both regimes in terms of plants’ average fresh weight accumulated per electrical energy unit consumed.

Leaf Injury and Dry Mass Production in Eggplant and Pepper Plant as Affected by Overnight Supplemental Lighting

Effect of overnight supplemental lighting at different light intensities following natural day length on growth and leaf injury of eggplant and pepper plant was investigated. Leaf chlorosis was observed with over 35 μmol m-2 s-1 PPFD and there was no correlation between light intensity and dry matter production in eggplant. On the other hand, pepper plants grew vigorously without any injurious symptoms even at 200 μmol m-2 s-1 PPFD. Total dry weight in pepper plant increased linearly with increase in light intensity. For instance, when supplemental light intensity was 100 μmol m-2 s-1, dry weight increase was 1.57 g/plant at 3 weeks after the initiation of light treatment, which was about 2 times higher than that in natural dark control (=0.71 g/plant) . When light intensity was 200 μmol m-2 s-1, the increase rate of total dry weight was 3 times higher than that in natural dark control. Increase rate of root dry weight was 4 times, but root length in the longest root was not different between the two treatments, suggesting that the lateral root growth was promoted by supplemental lighting. When sunlight intensity was reduced by 50%, the dry weight increase rate was 1.6, 1.5 and 2.0 times for leaf, stem and root, respectively, against 1.3, 1.2, 1.3 times in non-shaded plants. These results indicate that the enhancement of dry mass production in pepper plants by overnight supplemental lighting is more profound when the daytime solar radiation is low.

Effect of supplemental light intensity on white spruce, Engelmann spruce, and mountain hemlock seedlings grown under an extended photoperiod

Piceaglauca (Moench) Voss, Piceaengelmannii Parry and Tsugamertensiana (Bong.) Carr. were grown in an unheated "shelterhouse" container nursery, with a high pressure sodium vapour lamp providing a 19-h photoperiod and light intensities of 1600, 800, 400, 200, and 100 lx. The control seedlings received natural daylight and photoperiod. None of the light intensities effectively prevented terminal bud formation in the first two species while no terminal buds were formed at the 1600 lx level in the third one. Higher light intensities delayed the bud forming process in the first and third species, produced significant differences in the number of stem units of the first two, and resulted in larger mean stem unit lengths of the last two species. The longest seedling shoots of all three species were grown under light intensities of 800, 100, and 400 lx, respectively. There were no significant differences in seedling shoot weight, root weight, and root collar diameter among the five light intensity levels used to extend the photoperiod in the first growing season. Light intensity had little effect on 2-year shoot growth of all three species.