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Growth of tomatoes under Hybrid LED and HPS lighting
Abstract
The use of LEDs can be promising for greenhouse horticulture, but before it can be put into practice on a large scale more knowledge must be acquired on effects of LED lighting on crops. Furthermore, the growers will have to learn to grow their crops under LEDs and the efficiency of LEDs must increase even more. In order to gain more insight into the influence of LEDs on crop growth and production, an experiment was performed in the Wageningen UR greenhouses with a small Santa type tomato (‘Sunstream’) from October 2009 to June 2010. Four lighting treatments were applied, with each treatment in a separate greenhouse compartment: top lighting with HPS (1) or LED (2), and hybrid lighting with HPS above the crop in combination with LED lighting above the crop (3) or in between the canopy (interlighting) (4). The light intensity from the lamps in all treatments was maintained at 170 µmol m-2 s-1. The light was 50/50 divided between HPS and LED in the hybrid treatments. The climate in each treatment was adapted to the needs of the crop in each lighting system. The various lighting systems resulted in different greenhouse climates, in which more heating was required in the LED treatment and the least heating in the hybrid with interlighting. A strong crop developed under LED alone, and to maintain a proper crop balance the fruit load was altered by maintaining an extra tomato fruit per truss and increasing the stem density relative to that under HPS. The leaves of tomato grown under HPS were thinner and aged more rapidly in the winter than in the other treatments. Leaves lower in the canopy under LED alone or hybrid treatments had a higher photosynthesis capacity in the winter than leaves developed under HPS lighting. Differences in production were small, although the production under all LEDs was lower. There were only small differences in fruit quality. The amount of energy required per kilogram tomato was highest in the LED treatment and hybrid with top LED lighting. This was primarily due to the fact that a higher air temperature was necessary and these LEDs were cooled and the cost of cooling added to the use of energy. The consequences and future perspectives of the different types of supplementary lighting for crop growth and production as well as for crop management practices will be discussed.
... All these attributes contributed to a great deal of excitement around LEDs during their early days in horticulture (Massa et al., 2008), but also to quite some misinformation going around at the time (Mitchell et al., 2015). Early LEDs had a considerably lower PPE than HPS lamps (Dueck et al., 2012;Pattison, Hansen, et al., 2018). Despite this, the use of LEDs in greenhouses was considered an energy saving measure as early as 2008 (Van der Velden & Smit, 2009), and manufacturers of the time were claiming that LEDs were twice as efficient as HPS lamps (P. ...
... Moreover, it was quickly discovered that crops growing under LEDs require different climate control strategies, and greenhouses with LEDs require more heat from the greenhouse's heating system, compared to those with HPS lamps (Dueck et al., 2010(Dueck et al., , 2012. In one trial, LEDs realized a 37% saving in lighting input, but the total energy saving, including the need for heating, was only 11% (Dieleman et al., 2016). ...
... At the same time, the heat produced by HPS lamps reduces the demand from the greenhouse heating system (Ahamed et al., 2019). Several experiments have shown that the radiative heat from HPS lamps helps maintain the desired crop temperature, and that greenhouses equipped with LEDs require higher inputs from the heating system Dueck et al., 2012;Ouzounis et al., 2018). It follows, therefore, that the potential energy savings that are achievable by using LEDs may be offset by the need to provide more energy for heating. ...
... Although the role of carotenoids in photosynthesis is well appreciated, wavelengths other than red and blue had rarely been used in academic studies on the effect of LED lightings in tomato production. Consequently, there is a lot of information about the effect of red and blue light used as overhead-lighting, interlighting or hybrid-lighting (LEDs + HPS) on plant growth and yield of tomatoes (Dueck et al., 2011;Hogewoning et al., 2012;Gajc-Wolska et al., 2013;Gomez et al., 2013;Deram et al., 2014;Gómez and Mitchell, 2015;Tewolde et al., 2016;Gilli et al., 2018;Lanoue et al., 2019;Paponov et al., 2019). These studies showed that photosynthesis under a combination of red and blue light tends to be higher than under HPS lighting, but fruit yield is equal. ...
... Similar results in terms of the stem development were demonstrated for cucumbers, sweet basil, and tomatoes when a combination of blue, green, and red LEDs (Särkkä et al., 2017); blue, yellow, and red LEDs (Carvalho et al., 2016); or only green LEDs combined with daylight (Snowden et al., 2016) was used, respectively. Our yield data, however, are different to others, who have reported that a LED lighting with an emission spectrum that is optimized for chlorophyll absorption (blue and red) produces similar or even less yield than HPS lighting (Dueck et al., 2011;Gomez et al., 2013;Fanwoua et al., 2019). Although Frontiers in Plant Science | www.frontiersin.org ...
... Infrared radiation can have a substantial effect on photosynthesis and yield (Hernández and Kubota, 2015;Bergstrand et al., 2016). In our experiment, we measured the expected 1.5 • C higher leaf temperature under HPS, and as a consequence, a higher transpiration rate was also found in other studies (Dueck et al., 2011;Gajc-Wolska et al., 2013;Kim et al., 2019). Sage and Sharkey (1987) had shown that the rate of carbon dioxide uptake (e.g., photosynthesis) increased with increasing temperatures, until it reaches a critical point, after which it rapidly decreases. ...
Light emitting diodes (LEDs) are an energy efficient alternative to high-pressure sodium (HPS) lighting in tomato cultivation. In the past years, we have learned a lot about the effect of red and blue LEDs on plant growth and yield of tomatoes. From previous studies, we know that plants absorb and utilize most of the visible spectrum for photosynthesis. This part of the spectrum is referred to as the photosynthetically active radiation (PAR). We designed a LED fixture with an emission spectrum that partially matches the range of 400 to 700 nm and thus partially covers the absorption spectrum of photosynthetic pigments in tomato leaves. Tomato plants grown under this fixture were significantly taller and produced a higher fruit yield (14%) than plants grown under HPS lighting. There was no difference in the number of leaves and trusses, leaf area, stem diameter, the electron transport rate, and the normalized difference vegetation index. Lycopene and lutein contents in tomatoes were 18% and 142% higher when they were exposed to the LED fixture. However, the ß-carotene content was not different between the light treatments. Transpiration rate under LED was significantly lower (40%), while the light use efficiency (LUE) was significantly higher (19%) compared to HPS lighting. These data show that an LED fixture with an emission spectrum covering the entire PAR range can improve LUE, yields, and content of secondary metabolites in tomatoes compared to HPS lighting.
... Acclimation of plants to light quality has previously been demonstrated by HOGEWONING et al. (2007) as well as DUECK et al. (2012). Interestingly, data presented in this paper indicates that plants grown using HPS-lamps have less photosynthetic capacity when subjected to red/blue light from LEDs, as compared to plants that were grown in white LED-light for the whole cultivation period. ...
... The deviant climate in the treatments with HPS-lamps is attributable to the different characteristics of the HPS technology with respect to heat emission, as HPS-lamps emit most of its waste heat as IR-radiation. This fact was also stressed by PINHO (2008), HOGEWONING et al. (2007 and DUECK et al. (2012). The low radiant heat associated with the LED technology has often been described as an advantage (MORROW 2008;YEH and CHUNG 2009). ...
New lighting technologies of interest for the greenhouse horticulture have been introduced in the market during the last couple of years. The LED-technology has attended special interest from researchers and business, with attractive features such as long lifetime, high efficiency and possibilities for tailoring the light spectrum. In this study, common horticultural crops were grown in greenhouse conditions using different LED-light sources as well as HPS-lamps for supplementary lighting. Experiments were conducted both during increasing (spring) and decreasing (fall) natural light conditions. Biometric as well as photosynthetic evaluation of plant performance was performed. Plant parameters such as internodal length, development of flowers and lateral shoots, biomass accumulation (fresh/dry weight) and developmental time were recorded, in addition to photosynthesis and stomata conductance. Results indicate that biomass production was the highest when HPS-light was used. For photosynthesis and stomata conductance there were no differences with respect to the different treatments. Plant morphology was affected, with a reduction in stem elongation when red/blue or white LEDs were used as light source in ornamental plants grown during autumn period, and development was also delayed when LEDs were applied. However, in experiments performed during springtime there were no differences in plant morphology related to the different light sources.
... The data collected here were compared to those from studies using HPS lamps instead, as the LED amber light spectrum in this study is relatively similar to the HPS lamp spectrum (Figure 2). At moderate PPFD (<250 µmol·m −2 ·sec −1 ), higher or comparable plant productivity under HPS light is observed when compared to 460/655-nm LED light (PPFD <250 µmol·m −2 ·sec −1 ) (Bergstrand & Schüssler, 2013;Dueck et al., 2011;Gajc-Wolska et al., 2013;Gomez et al., 2013;Martineau et al., 2012). However, a contradictory result, in which amber light (580 to 600 nm) suppressed lettuce (L. ...
... light displayed a yellowish-green colour at ~800 μmol m −2 sec −1 and leaf yellowness directly increased with increased PPFD of amber and red light. If the photosynthesis and irradiance (P/I) curve data reported in the literature and from the current study are combined, results imply that using photosynthetic capacity data to correlate plant yields for high amber light conditions is inappropriate (Domurath et al., 2012;Dueck et al., 2011;Ménard et al., 2005). Further, results also suggest that amber light does not invoke photoprotection mechanisms as with UV and blue light. ...
... Studies with intra-canopy lighting partially replacing top lighting showed increased fruit yield in cucumber (Hovi et al., 2004;Hovi-Pekkanen and Tahvonen, 2008), an increase in sweet pepper fruit number and weight (Hovi-Pekkanen et al., 2006), and an increased net photosynthesis (PN) and photosynthetic capacity (Pmax) of cucumber leaves (Pettersen et al., 2010). In other studies no differences were found in whole plant biomass production or yield between top lighting and intra-canopy lighting (Trouwborst et al., 2010;Dueck et al., 2012;Goḿez and Mitchell, 2016;Yan et al., 2018). This lack of biomass gain could be related to a loss of total light interception due to extreme leaf curling by intra-canopy lighting as observed by Trouwborst et al. (2010) who used a large fraction of blue light. ...
... Furthermore, the location of the lamps in the canopy may potentially affect development of individual plant organs and dry matter partitioning and, hence, affect yield Further experimental studies are needed to investigate effects on light distribution, photosynthesis, growth, and yield by intra-canopy lighting. Studies with intra-canopy lighting partially replacing top lighting showed increased fruit yield in several studies (Hovi et al., 2004;Hovi-Pekkanen et al., 2006;Hovi-Pekkanen and Tahvonen, 2008) but having not effects in other studies (Trouwborst et al., 2010;Dueck et al., 2012;Goḿez and Mitchell, 2016;Yan et al., 2018). ...
In the past decade, the potential of positioning LED lamps in between the canopy (intra-canopy) to enhance crop growth and yield has been explored in greenhouse cultivation. Changes in spatial heterogeneity of light absorption that come with the introduction of intra-canopy lighting have not been thoroughly explored. We calibrated and validated an existing functional structural plant model (FSPM), which combines plant morphology with a ray tracing model to estimate light absorption at leaflet level. This FSPM was used to visualize the light environment in a tomato crop illuminated with intra-canopy lighting, top lighting or a combination of both. Model validation of light absorption of individual leaves showed a good fit (R² = 0.93) between measured and modelled light absorption of the canopy. Canopy light distribution was then quantified and visualized in three voxel directions by means of average absorbed photosynthetic photon flux density (PPFD) and coefficient of variation (CV) within that voxel. Simulations showed that the variation coefficient within horizontal direction was higher for intra-canopy lighting than top lighting (CV=48% versus CV= 43%), while the combination of intra-canopy lighting and top lighting yielded the lowest CV (37%). Combined intra-canopy and top lighting (50/50%) had in all directions a more uniform light absorption than intra-canopy or top lighting alone. The variation was minimal when the ratio of PPFD from intra-canopy to top lighting was about 1, and increased when this ratio increased or decreased. Intra-canopy lighting resulted in 8% higher total light absorption than top lighting, while combining 50% intra-canopy lighting with 50% top lighting, increased light absorption by 4%. Variation in light distribution was further reduced when the intra-canopy LEDs were distributed over strings at four instead of two heights. When positioning LED lamps to illuminate a canopy both total light absorption and light distribution have to be considered.
... Existing literature on HPS lighting and LED lighting mainly focusses at the energy conversion efficiency. For example, these lighting systems are compared in Nelson and Bugbee (2015) based on energy conversion efficiencies and in Dueck et al. (2012) and G omez and Mitchell (2014) the lighting systems are compared in a greenhouse experiment with tomatoes. Data from the experiment by Dueck et al. (2012) has been used to evaluate a model by Katzin et al. (2020) which aims to describe the qualitative difference between HPS lighting and LED lighting. ...
... For example, these lighting systems are compared in Nelson and Bugbee (2015) based on energy conversion efficiencies and in Dueck et al. (2012) and G omez and Mitchell (2014) the lighting systems are compared in a greenhouse experiment with tomatoes. Data from the experiment by Dueck et al. (2012) has been used to evaluate a model by Katzin et al. (2020) which aims to describe the qualitative difference between HPS lighting and LED lighting. Xu, Wei, & Xu, 2019 proposed a switching strategy for turning on and off LED lights using multi-objective optimisation is proposed, reporting an energy reduction of 30% with respect to rule-based control. ...
LED lighting is appointed as the successor of HPS lighting in greenhouses since it can lead to a more sustainable cultivation, i.e. it converts electrical energy into photosynthetically active radiation more efficiently. To quantify the effect of this more efficient conversion within the operation of the greenhouse system, an optimal controller is proposed to generate optimal control trajectories for the controllable inputs of the greenhouse. The optimal controller makes use of an economic objective function, i.e. the difference between income (yield×productprice) and cost of resources (resourceuse×cost). The performance of this optimally controlled greenhouse system is compared with respect to the state-of-the-practice. Simulation experiments suggest optimal control can increase the economic objective by 10% to 65.14€.m−2 compared to 58.96€.m−2 for the state-of-the-practice, for tomatoes cultivated in a Dutch weather conditions. The model of the optimally controlled greenhouse is used to compare the performance of different lighting systems, i.e. no lighting, HPS lighting and LED lighting. An increase of 9% in the operational return is observed for LED lighting compared to HPS lighting. The electricity that is saved due to the more energy-efficient conversion in the LED lighting results in a 30% decrease in carbon footprint when comparing a greenhouse with LED lighting to a greenhouse with HPS lighting.
... Despite this, many studies that examined the energy saving potential of LEDs in greenhouses focused on the savings of the lighting system only [10,12,16,17], and did not quantify the influence of the lighting system on heat demand. Only a few limited studies reported on how LEDs influence the total energy demand of the greenhouse [18], and these suggest that effects on total energy saving might be disappointing. For example, a hybrid system combining LEDs and HPS lamps was compared to a full-LED system. ...
... where x is the controlled variable (e.g., the indoor temperature), setPoint is the desired setpoint for the controlled variable (e.g., 18.5 • C during the dark period), pBand is a band defining the width of the proportional control, and Action defines the controller action. At Action = 1, the controller is at full capacity (e.g., heating is at full power), at Action = 0 the controller is off. ...
Greenhouses in high latitudes consume vast amounts of energy for heating and supplemental lighting. Light emitting diodes (LEDs) have been suggested as having great potential for reducing greenhouse energy use, as they are extremely efficient at converting electricity to light. However, LEDs emit very little heat, which must be compensated by the greenhouse heating system. Thus, it is unclear how much energy can be saved by LEDs when the need for extra heating is taken into account. This study presents a first analysis of the energy demands for greenhouses transitioning from high-pressure sodium (HPS) to LED lighting, providing a quantification of the total energy savings achieved by LEDs. Model simulations using GreenLight, an open source greenhouse model, were used to examine a wide range of climates, from subtropical China to arctic Sweden, and multiple settings for indoor temperature, lamp intensity, lighting duration, and insulation. In most cases, the total energy saving by transition to LEDs was 10–25%. This value was linearly correlated with the fraction of energy used for lighting before the transition, which was 40–80%. In all scenarios, LEDs reduced the energy demand for lighting but increased the demand for heating. Since energy for lighting and heating is often derived from different origins, the benefits of a transition to LEDs depend on the environmental and financial costs of the available energy sources. The framework provided here can be used to select lighting installations that make optimal use of available energy resources in the most efficient and sustainable manner.
... At the same time, the heat produced by HPS lamps reduces the demand from the greenhouse heating system (Ahamed et al., 2019). Several experiments have shown that the radiative heat from HPS lamps helps maintain the desired crop temperature, and that greenhouses equipped with LEDs require higher inputs from the heating system (Dieleman et al., 2015;Dueck, Janse, Eveleens, Kempkes, & Marcelis, 2012;Ouzounis, Giday, Kjaer, & Ottosen, 2018). It follows, therefore, that the potential energy savings that are achievable by using LEDs may be offset by the need to provide more energy for heating. ...
... Data from an experiment comparing HPS and LED top-lights was used for evaluating the GreenLight model. The experiment was described in detail by Dueck et al. (2012Dueck et al. ( , 2010. In this experiment, tomato plants (Solanum lycopersicum cv. ...
Greenhouse models are important tools for the analysis and design of greenhouse systems and for offering decision support to growers. While many models are available, relatively few include the influence of supplementary lighting on the greenhouse climate and crop. This study presents GreenLight, a model for greenhouses with supplemental lighting. GreenLight extends state of the art models by describing the qualitative difference between the common lighting system of high-pressure sodium (HPS) lamps, and the newest technology for horticultural lighting - the light-emitting diodes (LEDs). LEDs differ from HPS lamps in that they operate at lower temperatures, emit mostly convective heat and relatively little radiative heat, and can be more efficient in converting electricity to photosynthetically active radiation (PAR). These differences can have major implications on the greenhouse climate and operation, and on the amount of heat that must be supplied from the greenhouse heating system. Model predictions have been evaluated against data collected in greenhouse compartments equipped with HPS and LED lamps. The model predicted the greenhouse's heating needs with an error of 8–51 W m⁻², representing 1–12% of the measured values; the RMSE for indoor temperature was 1.74–2.04 °C; and the RMSE for relative humidity was 5.52–8.5%. The model is freely available as open source MATLAB software at https://github.com/davkat1/GreenLight. It is hoped that it may be further evaluated and used by researchers worldwide to analyse the influence of the most recent lighting technologies on greenhouse climate control.
... Several recent studies have compared fruit yield under LEDs and HPS lighting in high wire greenhouse crops such as tomato (Solanum lycopersicum L.; Deram et al., 2014;Dueck et al., 2012;Gómez and Mitchell, 2016), pepper (Capsicum annuum; Guo et al., 2016) and cucumber (Cucumis sativus; Trouwborst, 2010;Särkkä et al., 2017). They showed that using LEDs mostly results in similar (Trouwborst, 2010;Dueck et al., 2012;Dieleman et al., 2016;Gómez et al., 2013) or improved (Deram et al., 2014;Hao et al., 2016) crop yield compared to HPS lighting. ...
... Several recent studies have compared fruit yield under LEDs and HPS lighting in high wire greenhouse crops such as tomato (Solanum lycopersicum L.; Deram et al., 2014;Dueck et al., 2012;Gómez and Mitchell, 2016), pepper (Capsicum annuum; Guo et al., 2016) and cucumber (Cucumis sativus; Trouwborst, 2010;Särkkä et al., 2017). They showed that using LEDs mostly results in similar (Trouwborst, 2010;Dueck et al., 2012;Dieleman et al., 2016;Gómez et al., 2013) or improved (Deram et al., 2014;Hao et al., 2016) crop yield compared to HPS lighting. Much less attention has been paid to investigating the effects of LED lighting on fruit quality. ...
Understanding how greenhouse crops respond to supplemental lighting with light-emitting diodes (LEDs) compared with traditional lighting systems is essential to utilize the full potential of LEDs and their further adoption in energy efficient greenhouses. This study quantified the effects of supplemental lighting with high-pressure sodium (HPS) lamps and LED light on the dynamics of fruit growth and composition in tomato (Solanum lycopersicum L.). Two tomato genotypes (‘Foundation’ and ‘Progression’) were grown under daylight supplemented either with HPS (125 μmol m−2 s−1) combined with red/blue LED lighting (106 μmol m−2 s−1, HPS + LED light treatment) or red/blue LED light only (106 110 μmol m−2 s−1, LED + LED light treatment); and two genotypes (‘Foundation’ and ‘NUN09204’) under daylight supplemented either with red/blue LED light (200 μmol m−2 s−1, red/blue LED light treatment) or red/blue LED + far-red LED light (200 μmol m−2 s−1 + 40 μmol m−2 s−1, red/blue + far-red LED light treatment). Fresh weight and composition in glucose, fructose, sucrose, starch, citric acid and malic acid of tomato fruits at different stages of development were measured and analyzed in terms of three main underlying components: water dilution, dilution by soluble and storage compounds and metabolism. Growing fruits under the LED + LED compared to the HPS + LED light treatments increased average fruit fresh weight in all genotypes. The red/blue + far-red LED light treatment increased the production of soluble sugar, increased the dilution by soluble and storage compounds, and reduced water dilution leading to a strong increase in glucose, fructose and sucrose concentration in the pericarp. The LED + LED light treatment did not affect the metabolism of fruit biochemical compounds compared to the HPS + LED light treatments, but caused small changes in water dilution, which were reflected in the concentration of biochemical compounds. Dilution and metabolism were involved in genotypic differences in fruit composition. Our results show that altering the spectral composition of the supplemental light in energy efficient greenhouses can be done without an effect on fruit quality or even with an improvement of tomato fruit quality. Possible physiological processes underlying these light-induced changes in fruit biochemical compounds during fruit development in different genotypes were discussed.
... Due to its miniaturization and high level of automation, experiments can be conducted more efficiently, and large amounts of experimental data can be collected in a shorter time [48]. Moreover, the system offers high environmental stability, ensuring consistency and repeatability in experimental conditions [49]. However, conventional micro-plant factories typically have inlets and outlets at the top and bottom, which can lead to significant heterogeneity in the internal microenvironment. ...
The uniformity of the cultivation environment in a micro-plant factory plays a critical role in ensuring the consistent growth of seedlings, and an optimal airflow pattern is the key to maintaining environmental uniformity. This study applied computational fluid dynamics (CFD) modeling to compare the effects of six different ventilation modes on the microclimate within the cultivation space. In cases 1 and 2, the inlet was positioned at the top, while the outlets were located at both the bottom and the top of the side walls. For cases 3 to 6, a side-inlet and side-outlet ventilation system was employed across the three cultivation layers. Case 4 maintained consistent inlet and outlet airflow speeds, whereas cases 3, 5, and 6 featured airflow settings that either increased or decreased progressively from the top layer to the bottom. Notably, case 6 was characterized by a more compact arrangement of cultivation racks within the space, which were positioned closer to the outlet than in the other cases. In case 1, the air inlets were positioned at the top, while the outlets were located on both side walls at the lower layer of cultivation. In contrast, case 6 used a side-inlet and side-outlet ventilation strategy, in which the airflow speed of the inlets decreases progressively from the top to the bottom of the cultivation layers. Additionally, the cultivation racks in case 6 were arranged more compactly and positioned closer to the outlet of the cultivation space. The relative standard deviation (RSD) was used to evaluate the uniformity of the airflow velocity (m/s), temperature (K), and relative humidity (%) within the crop-growing area. The results indicated that, among all the scenarios, case 6 demonstrated the lowest RSD values for the airflow velocity, temperature, and relative humidity, with reductions of 18.34%, 0.12%, and 2.05%, respectively, compared to the control group (case 1). Based on the ventilation design of case 6, a micro-plant factory was developed featuring a bidirectional flow fan, air conditioning, and PWM fans for the coordinated control of air circulation within the seedling cultivation space, along with adjustable cultivation layer heights and shelf spacing. The accuracy of the CFD model for the micro-plant factory was validated with normalized root mean square error (NMSE) for cultivation layer heights of 250 mm, 300 mm, and 350 mm. The NMSE values comparing the simulated and measured results for the airflow velocity, temperature, and relative humidity were found to be 0.032, 0.0020, and 0.0022; 0.031, 0.0021, and 0.0018; and 0.046, 0.0021, and 0.0021, respectively. These findings indicate that the established CFD model can reliably predict the microenvironment within the micro-plant factory.
... Leaves lower in the canopy have a lower photosynthetic capacity due to acclimation to lower light levels (Trouwborst et al. 2011). Providing light to leaves lower in the canopy (ICL) did indeed increase leaf photosynthetic capacity (Dueck et al. 2012). By supplying light not only on top of the canopy, but also within the canopy, a more homogeneous vertical light distribution can be achieved. ...
This study compared supplemental white light-emitting diode (LED) light provided on top of the canopy (top-light) or partially on top and partially as intracanopy light (ICL) in high-wire cucumber ( Cucumis sativus ) and tomato ( Solanum lycopersicum ) crops. The aim was to determine the effects of partially substituting top-light by ICL on fruit yield and its underlying yield components. For each crop, three replicate Venlo glasshouse compartments were used. Two cucumber (HiPower and Skyson) and two tomato cultivars (Brioso and Merlice) were planted in the second half of Oct 2020 and grown on stone wool for a period of 15 weeks (cucumber) or 20 weeks (tomato). Light was supplied at either a light intensity of 250 or 375 µmol⋅m ⁻² ⋅s ⁻¹ , provided either as 100% top-light or as 67% (2/3) top-light and 33% (1/3) ICL. For cucumber at the higher light intensity, 50% more fruits were retained and for tomato at the higher light intensity, planting density was 50% higher to keep the plants balanced in terms of source-to-sink ratio. Substituting 33% of top-light with ICL resulted on average in an increase of 17% in fresh fruit yield for both cucumber and tomato. This increase was twice as high at the higher light intensity (20% to 24%) compared with the lower light intensity (10% to 12%). For both cucumber and tomato, the higher yield for ICL treatments resulted mainly from higher total plant dry weight, whereas partitioning to the fruits was hardly affected. For both crops, the higher plant dry weight resulted from a higher light use efficiency. Increasing light intensity from 250 to 375 µmol⋅m ⁻² ⋅s ⁻¹ resulted in 38% higher total daily light integral (including solar radiation) and 36% to 37% higher total plant dry weight in cucumber. In tomato, the higher light intensity resulted in 33% higher daily light integral and 36% to 40% total plant dry weight. These values are in agreement with the rule of thumb that 1% increment in light results in 1% increase in plant growth. For cucumber, partially substituting top-light by ICL as well as increasing light intensity resulted in longer and greener fruits, whereas tomato fruit quality (Brix, pH) was unaffected by ICL or light intensity. In conclusion, partially substituting top-light by intracanopy light increased fruit yield and this was even more so at higher than at lower supplemental light intensities.
... However, contrasting results regarding the effect of light sources on yield are reported in the literature. For example, for tomatoes, Dueck et al. (2012a) described a lower production under LEDs than under HPS lights, while Wacker et al. (2022) reported a 10% higher tomato yield under LEDs compared to HPS lights and concluded that switching from HPS lamps to LEDs enables increasing productivity. The significantly lower yield of Magnum under LEDs in the second winter (Figure 2(b)) was possibly caused by a lower number of pollinated flowers. ...
Supplementary lighting is essential to maintain year-round production in Iceland due to the extremely low natural light level in winter. In this research, the effects of high-pressure vapour sodium lamps (HPS) are compared to light emitting diodes (LED), both with similar photosynthetic photon flux density (PPFD). Strawberries (Fragaria x ananassa cv. ‘Sonata' and cv. ‘Magnum') were grown either under HPS lights or LEDs and 16°C/8°C (day/night). However, in the second winter, the day temperature was increased to 19°C under LEDs. The results showed that under the same temperature set points, the development of the flowers and the harvest was delayed by two weeks under LEDs due to a lower leaf, substrate and air temperature. However, when temperature set points were adapted, no delay under LEDs was observed. LEDs did not lead to higher yield, but to a higher energy use efficiency, while light use efficiency behaved contrary. Economic calculations clearly demonstrate that it is not justified to switch from HPS lights to LEDs. Instead, it is rather recommended to emphasise a high-yielding variety like Sonata in winter-growing of strawberries.
... Although the luminaire efficacies, energy costs, and equipment cost values have rapidly advanced since the publication of their work, the authors provided a solid framework for comparing some of the important differences between the two lighting technologies. Recent studies have taken an application-based approach to investigating the total energy savings potential of LED lighting in greenhouses when also considering the increase in heating energy required by switching to LEDs from HPS sources (Dieleman et al. 2016;Dueck et al. 2011;Katzin et al. 2021). Katzin et al. (2021) found that transitioning from HPS to LED sources in greenhouses saved 40% in lighting energy. ...
Photometric simulations using both daylight and electric lighting were performed to compare the energy use of conventional high-pressure sodium (HPS) greenhouse lighting to that of light-emitting diode (LED) lighting. Photometric simulations of a hypothetical greenhouse were performed in three different geographic locations in the United States with widely different annual daylight availability: Albany, NY, Fairbanks, AK, and Phoenix, AZ. Simulation conditions included summer and winter, overcast and clear skies, and several lighting layouts and distributions. The analysis showed that, while maintaining the criteria levels of photosynthetic photon flux density, lighting energy savings were primarily attributable to increased LED source efficacy rather than HPS. Secondary energy savings were attributable to the ability to continuously dim LED lighting in response to daily and seasonal changes in daylight. Despite options for LED luminaires with a slim form factor, reduced crop shading compared with larger conventional HPS luminaires did not result in significant lighting energy savings.
... Lee, Elliott, & Pattison, 2020). One evidence of this is the fact that LEDs are often used not as a replacement for existing HPS lamps, but rather as an addition to them (Vanlommel, Huysmans, Bosmans, Vanderbruggen, & van Delm, 2020), either above the crop canopy (toplights), or within the canopy (interlights) (Dueck, Janse, Eveleens, Kempkes, & Marcelis, 2012;Moerkens, Vanlommel, Vanderbruggen, & Van Delm, 2016). The result is thus an unprecedented increase in the intensity of supplemental lighting used in greenhouses. ...
lighting heating modelling energy use LED High-tech greenhouses are characterised by high yields and high energy consumption. Current trends towards expanded use of supplemental lighting further increase the intensity of crop production and energy use, and it is expected that the availability of light-emitting diodes (LEDs) will accelerate this trend. At the same time, an increase in greenhouse lighting reduces the heating energy needed from the heating system. This study presents a novel concept for greenhouses, where both lighting and heating are derived exclusively from lamps. Such greenhouses can be highly efficient, as light is used both for crop growth and for heating. If the electric grid is based on renewable sources, such greenhouses can also be carbon-neutral and fossil-free. By using model simulations for a tomato greenhouse in the Netherlands, it was found that such greenhouses could be realised by employing a heat storage system with a heat storage capacity of 2 MJ m À2 and LEDs with a power capacity of 150 W m À2 and a photosynthetic photon flux density (PPFD) of 450 mmol m À2 s À1. The greenhouse heated by light was predicted to have 44% higher yields and 60% higher energy inputs than a reference greenhouse, equipped with a boiler and LEDs with a PPFD of 200 mmol m À2 s À1. This result was part of a general trade-off that was found between yield and energy efficiency. This exploration helped identify avenues for further improvement of the energy efficiency of greenhouses heated by lamps, highlighting their promise as a potential new direction in greenhouse intensification.
... LED lighting can be used to overcome the problem of insufficient lighting time in greenhouses during the winter in northern China [14][15][16]. Previous research has demonstrated that LED supplementary lighting between plants improves the light environment of the middle and lower crop leaves, promotes plant photosynthesis, and increases tomato yield [17][18][19]. ...
Using full-spectrum LED lights, six light treatments of 11 h, 12 h, 13 h, 14 h, 15 h, and CK (greenhouse natural light) were designed to examine the response of Populus euramericana plantlets to light duration in the greenhouse. Every 15 days during the 150-day experiment, plantlet height (H), ground diameter (GD), number of nodes (NN), number of leaves (NL), and the relative chlorophyll content(SPAD) were measured. The response of plantlets to different light durations was demonstrated by establishing and screening growth models, and rhythm and relative chlorophyll content were statistically analyzed. The light duration had a significant effect on the H and GD of Populus euramericana, and their growth was positively correlated with light duration. The short full-spectrum LED lighting duration will affect the rhythm and prematurely halt the growth of H, but the GD will continue to expand. The Gomperz model has the best fitting effect for the growth of Populus euramericana plantlets under LED lighting, with all R2s values greater than 0.89. Long light duration has a greater growth potential, and the rapid growth lasts longer. The delay in the cessation of the increase in the NN was a result of the increased illumination time. Compared with natural light, LED light lessens the NL. Poplar plantlets will have a lower SPAD value if the light duration exceeds 14 h. In the process of growing plantlets in the greenhouse, both light quality and light duration should be considered. In actual production, a combination of natural and artificial light can improve efficiency.
... Tomato stem density has been increased by LED interlighting, especially in summer [60]. This has led to studies on the positive effects for plant growth and production of LED interlighting as a sole source of SL or in combination with overhead point sources or overhead-distributed sources [61][62][63][64]. Nowadays, toplighting alone or with interlighting is the SL system most widely used in horticulture, because overhead lights give better artificial light distribution in the greenhouse or grow chamber, and the maintenance and installation costs of toplight LED are lower than those of interlight LED. ...
High-tech greenhouses and artificial light applications aim to improve food production, in line with one of the sustainable development goals of the UN Agenda 2030, namely, “zero hunger”. In the past, the incandescent lamps have been used for supplementary lighting (SL) at higher latitudes to increase greenhouse production during the dark season. Light-emitting diodes (LED) have been replacing gas discharge and incandescent lamps, and their development is expanding SL applications in different agricultural scenarios (e.g., urban farming, middle latitudes). In fact, recent research on LED applications in Mediterranean greenhouses have produced encouraging results. Since middle latitudes have a higher daily light integral (DLI) than higher latitudes in the dark season and climate conditions influence the installed power load of greenhouses, LED installation and management in Mediterranean greenhouses should be different and less expensive in terms of investment and energy consumption. Accordingly, the aim of this review is to outline the state of the art in LED applications and development, with a focus on latitude-related requirements. Tomato was used as a representative crop.
... Each light source needs its climate set points for the optimum growth performance of the plant (Dueck et al., 2011). It has been reported that different light sources can alter the metabolite status in plant bodies (Fukuda, 2019). ...
We investigated the effects of growth performance of three plant species parsley (Petroselinum crispum), lettuce (Lactuca sativa) and cress (Lepidium sativum) under the three different lighting sources, Light-Emitting Diode lamp (LED; 200w), High-Pressure Sodium lamp (HPS; 200w) and Fluorescent lamp (FLO; 200w) in an aquaponic system. A total number of 43 koi fish (Cyprinus carpio var. koi) with 3628 g total biomass (84.4 g per individual) were used. The fish used in the experiment recorded 36% growth and reached an average individual weight of 132.7 g at the end of the experiment. The parsley plant was measured as 8.76 ±7.32 g; 7.45 ±4.13 g; 2.04 ±1.96 g weight after 45 days, the lettuce plant was 54.09 ± 25.60 g; 60.83 ±19.39 g; 17.81 ±6.40 g weight after 54 days, cress plant was 1.03 ±0.58 g; 1.15 ±0.46 g; 1.31 ±0.58 g weight after 42 days, under the HPS, LED, and FLO light sources, respectively. HPS and LED light sources in lettuce and parsley showed better plant development than the FLO, while no significant difference occurred in cress plants under three light conditions. We conclude that using HPS or LED lights in indoor aquaponics has the potential to produce good quality and adequate amounts of plants.
... mol m −2 d −1 [7,8]. Moreover, the fruit yield under LEDs was lower than that of HPS under different lighting treatments (PPFD 170 µmol m −2 s −1 ): 1. HPS toplighting, 2. LED toplighting, 3. hybrid HPS and LED toplighting, 4. hybrid HPS toplighting and LED interlighting [19]. Furthermore, the addition of LED interlighting to HPS toplighting decreased light-use efficiency [9]. ...
Supplemental lighting is common in northern countries or during winter greenhouse tomato production. We investigated the effect of supplemental lighting treatments on cherry tomato (‘Jun-Ama’) yield, productivity (light-use efficiency (LUE) and energy-use efficiency (EUE)), and fruit quality under high irradiance (average greenhouse daily light integral (DLI) = 14.5 mol m⁻² d⁻¹). Supplemental lighting treatments contained average DLIs of 2.7, 4.9, and 7.6 mol m⁻² d⁻¹ for interlighting, toplighting, and inter- + toplighting, respectively. Supplemental LED lighting increased fruit yield by 18, 41, and 40% with inter-, top-, and inter- + toplighting, respectively, compared with the control. Interlighting increased fruit number (+11%), and top- and inter- + toplighting also increased the fruit number (+26%, +27%) and weight (+10%, +10%), respectively. LUE and EUE were comparable between inter- and toplighting, while inter- + toplighting decreased LUE by 21 and 38%, and EUE by 38 and 31% compared with inter- and toplighting, respectively. All LED supplemental treatments significantly increased total soluble solids compared with the control. Total acidity and lycopene content were unchanged in all treatments. In conclusion, LED supplemental lighting with inter- or toplighting improved cherry tomato yield and quality, but inter- + toplighting was inefficient under high irradiation.
... This study showed that the plants in the groups treated with SL presented their maximal PI abs value earlier than plants in the CK group, which implies that SL accelerated the formation of the PSII apparatus. Dueck et al. [37] found that, in comparison with those under LED supplemental lighting, the leaves of tomato plants grown under HPS lamp-provided supplemental lighting were thinner and aged more rapidly in winter. Our results showed that the plants were taller and the stem thickness was reduced following the HPS treatment compared with the LED treatment. ...
The addition of supplemental light (SL) is an effective way to offset insufficient lighting. Although it is commonly believed that SL increases leaf photosynthesis and therefore improves yield and fruit flavor, the mechanism underlying the effects of SL on the photosystem II (PSII) apparatus remains unclear, and SL leads to high energy consumption. In order to save energy, we investigated the physiological status of the PSII apparatus, plant growth parameters and fruit parameters under two types of overhead SL with a low daily energy consumption of 0.0918 kWh m⁻². The results showed that SL significantly increased the leaf chlorophyll content from full unfolding to yellowing. However, a remarkable increase in the absorption flux per cross-section (ABS/CS), the quantum yield of electron transport (φEo) and the performance index (PIabs) was observed only in a relatively short period of the leaf life cycle. SL also enhanced the fruit yield and quality. The obviously increased ΔVK and ΔVJ components of the chlorophyll fluorescence induction kinetic (OJIP) curve, along with the significantly decreased PIabs from days 40–60 after unfolding in the SL-treated groups, resulted in more rapid leaf aging and earlier fruit ripening compared with the control plants (CK). Therefore, an energy-friendly SL strategy can alter the physiological status of the PSII apparatus, affecting yield and fruit quality and maturity.
... Also heat radiation (HPS lamps are warmer and heat plants more from above) could influence the microclimate favourably to reduce BER under LED compared to HPS supplemental lit compartment. Under HPS lamps there was more near infra-red and heat radiation on the plant which likely resulted in more transpiration (Dueck et al. 2012), and hence more water uptake. This may have led to the slightly higher EC found in the stone woll slabs in the HPS compartment. ...
LED lighting has emerged as alternative to the current HPS standard in greenhouse production. However little is known about the impact on fruit quality under the different light spectra. We grew a biparental tomato RIL population between September 2019 and January 2020 under two commercial greenhouse supplemental lighting conditions, i.e. HPS, and 95% red/5% blue- LED, of about 220 µmol m ⁻² s ⁻¹ at maximum canopy height for 16 h per day. Differences in Brix and blossom-end rot (BER) between the two light conditions were observed and we studied the genetic influences on those traits, separating genetics located on chromosomes from genetics located in plastids. The Brix value was on average 11% lower under LED than under HPS supplemental lighting. A LED-light specific QTL for Brix was identified on chromosome 6. This QTL can be of interest for breeding for tomato varieties cultivated under LED supplemental lighting. A Brix-QTL on chromosome 2 was found for both light conditions. In our study fewer plants developed BER under LED supplemental lighting than under HPS. We identified a novel genetic locus on chromosome 11 for the incidence of BER that lead to a difference in about 20% of fruits with BER. This genetic component was independent of the light.
... In both March and May, leaves exposed to 185 µmol m −2 s −1 ICL showed a higher A max , 58 and 42%, respectively, when compared to no ICL. ICL resulting in increased leaf photosynthetic capacity for lower leaves in the canopy was also shown by Dueck et al. (2012) for tomato and Pettersen et al. (2010) for cucumber. ...
High market price and low availability of local winter and spring production has stimulated production of blackberries in glasshouses at northern latitudes. For this production, light is the main limiting factor. We investigated the potential of intercanopy lighting (ICL) using light emitting diodes (LEDs) to improve blackberry fruit yield in a crop with a spring and an autumn production cycle. During the spring production cycle three light treatments were applied: only natural light (no ICL), 93 or 185 μmol m–2 s–1 ICL In summer the lateral shoots were cut back and 93 μmol m–2 s–1 ICL was applied to all plants after cutting back, investigating a possible carryover effect of supplemental light in spring on autumn production. Fresh fruit yield in spring increased by 79 and 122% with 93 and 185 μmol m–2 s–1 ICL, respectively, compared to no ICL. This represents 3.6 and 2.8% increase in harvestable product for every additional 1% of light. A yield component analysis and leaf photosynthesis measurements were conducted. Maximum photosynthetic capacity (Amax) for leaves at 185 μmol m–2 s–1 ICL was about 50% higher, and LAI was 41% higher compared to no ICL. ICL increased the number of fruiting laterals per cane, and this explained 75% of the increase in yield. ICL at 185 μmol m–2 s–1 resulted in a higher yield compared to no ICL, primarily as a result of higher total dry matter production. Furthermore, a higher fraction of dry matter partitioned to the fruits (0.59 compared to 0.52) contributed to yield increase, whereas fruit dry matter content and fruit quality (sugar and acid content) was not affected by ICL. Averaged over the three light treatments autumn yield was 47% lower than spring yield. Autumn yield was 10% higher for plants at ICL 93 μmol m–2 s–1 in spring and 36% higher for plants at 185 μmol m–2 s–1 in spring compared to no ICL in spring. This increased autumn yield was caused by more fruiting laterals (less necrotic buds). It is concluded that management practices in spring can have a carryover effect on the autumn production. This is the first scientific paper on the potential for applying LED ICL in blackberries. Further research should focus on optimal intensity of ICL, positioning of supplementary lighting and economic feasibility.
... Amber-biased (~590-610 nm) high pressure sodium (HPS) lamps were the preferred choice over LEDs in commercial greenhouse facilities until recently, as plant productivity varies with respect to crop choice and growth stages when grown under LED light [13,15]. Experiments that compare HPS lamps to blue/red LEDs for plant growth and yield are a major focus of plant lighting studies [15][16][17][18][19]. LEDs have emerged as the prominent plant lighting system over HPS, mainly because of their higher energy efficiency. ...
Red and blue light are the principal wavelengths responsible for driving photosynthetic activity, yet amber light (595 nm) has the highest quantum efficiency and amber-rich high pressure sodium lamps result in superior or comparable plant performance. On this basis, we investigated how lettuce plant growth and photosynthetic activity were influenced by broad and narrow light spectra in the 590–630 nm range, by creating amber and red light-emitting diode (LED) spectra that are not commercially available. Four different light spectra were outfitted from existing LEDs using shortpass and notch filters: a double peak spectrum (595 and 655 nm; referred to as 595 + 655-nm light) that excluded 630-nm light, 595-nm, 613-nm, and 633-nm light emitting at an irradiance level of 50 W·m−2 (243–267 µmol·m−2·s−1). Shifting LED wavelengths from 595 nm to 633 nm and from 595 nm to 613 nm resulted in a biomass yield decrease of ~50% and ~80%, respectively. When 630-nm light is blocked, lettuce displayed expanded plant structures and the absence of purple pigmentation. This report presents a new and feasible approach to plant photobiology studies, by removing certain wavelengths to assess and investigate wavelength effect on plant growth and photosynthesis. Findings indicate that amber light is superior to red light for promoting photosynthetic activity and plant productivity, and this could set precedence for future work aimed at maximizing plant productivity in controlled environment agriculture.
... Also heat radiation (HPS lamps are warmer and heat plants more from above) could in uence the microclimate favourably to reduce BER under LED compared to HPS supplemental lit compartment. Under HPS lamps there was more near infra-red and heat radiation on the plant which likely resulted in more transpiration (Dueck et al. 2012), and hence more water uptake. This may have led to the slightly higher EC found in the stone woll slabs in the HPS compartment. ...
LED lighting has emerged as alternative to the current HPS standard in greenhouse production. However little is known about the impact on fruit quality under the different light spectra. We grew a biparental tomato RIL population between September 2019 and January 2020 under two commercial greenhouse supplemental lighting conditions, i.e. HPS, and 95% red/ 5% blue- LED, of about 220 µmol m − 2 s − 1 at maximum canopy height for 16h per day. Differences in Brix and blossom-end rot (BER) between the two light conditions were observed and we studied the genetic influences on those traits, separating genetics located on chromosomes from genetics located in plastids. The Brix value was on average 11% lower under LED than under HPS supplemental lighting. A LED-light specific QTL for Brix was identified on chromosome 6. This QTL can be of interest for breeding for tomato varieties cultivated under LED supplemental lighting. A Brix-QTL on chromosome 2 was found for both light conditions. In our study fewer plants developed BER under LED supplemental lighting than under HPS. We identified a novel genetic locus on chromosome 11 for the incidence of BER that lead to a difference in about 20% of fruits with BER. This genetic component was independent of the light.
... Moreover, if the lamps for lighting are divided into the upper and middle levels, then the upper light should be turned off after a 12-hour photoperiod to protect the environment. The average level of lighting with LED elements, can be turned on at night without any harm for the environment and the nearest residential areas [18]. ...
Introduction. The article deals with the conditions for growing greenhouse plants. Supplementary lighting supports the process of plant photosynthesis and the microclimate in the greenhouse. The authors suggest the ways to reduce energy consumption in greenhouses by controlling the microclimate and process of supplementary lighting in greenhouses.
Materials and Methods. Special lighting and temperature are required for growing greenhouse plants. A method of efficient plant growing is light and temperature control. The development of a control algorithm requires the mathematical models that relate the process of photosynthesis to the microclimate parameters. There are given the mathematical models based on the experimental data.
Results. The control system and algorithm to control plant-growing conditions have been developed to maintain the greenhouse microclimate. LED lamps are used to control the lighting process. The authors present the developed block diagram of the control system, which contains four channels responsible for the main energy-intensive microclimate factors. The description of the algorithm of the greenhouse light-temperature control is given.
Discussion and Conclusion. In conclusion, the need to maintain the greenhouse microclimate and supplementary lighting with the different radiation spectrum for the efficient cultivation of greenhouse plants is shown. The developed structure and control algorithm for the supplementary plant lighting process and greenhouse illumination through using LED lamps help reduce energy consumption.
... Indeed, LED lights provide tunable wavelengths to be matched to plant photoreceptors, including phytochrome and cryptochrome, in order to have optimal plant growth in terms of morphology (e.g., height, leaf area, thickness, and stem length) and quality (e.g., metabolites) [7][8][9][10][11]. Therefore, this provides a new opportunity to manipulate the quality and quantity of vegetable products for markets and meet the demands of retailers in a future perspective involving artificial intelligence control over a real-time autonomous horticultural system [12]. ...
Featured Application
The specific application of this work is related to basil cultivation in indoor horticulture and is devoted to the investigation of specific light recipes and fertilizers addition to promote its germination and growth in a controlled environment.
Abstract
This study aims to optimize the conditions for “Genovese” basil (Ocimum Basilicum) germination and growth in an indoor environment suitable for horticulture through a synergic effect of light and fertilizers addition. In fact, several studies determined that specific light conditions are capable of enhancing basil growth, but this effect is highly dependent on the environmental conditions. In this study, the effect of different light sources was determined employing a soil with a negligible amount of fertilizer, demonstrating substantial improvement when light-emitting diode (LED) lights (hyper red and deep blue in different combinations) were applied with respect to daylight (Plants height: +30%, Total fresh mass: +50%). Thereafter, a design of experiment approach has been implemented to calculate the specific combination of LED lights and fertilizer useful to optimize the basil growth. A controlled-release fertilizer based on nitrogen, phosphorus, and potassium (NPK) derived from agro-residues was compared with a soil enriched in macronutrients. The results demonstrate significant improvements for the growth parameters with the employment of the controlled-release NPK with respect to enriched soil combined with a ratio of hyper red and deep blue LED light equal to 1:3 (Total fresh mass: +100%, Leaves number: +20%).
... High-pressure sodium light fixtures emit radiation in the wavelength range of 800-2500 nm, and this radiation can increase leaf temperature by 0.5-2.0 °C in the greenhouse (Bergstrand and Schussler 2013;Dueck et al. 2012;Islam et al. 2012;Nelson and Bugbee 2015). Even though the air temperature measured at the leaf boundary layer in the HPS light treatment was only 0.5-0.7 °C higher than that in the LED treatments (Table 2), the actual leaf temperature was likely higher (not measured in this study). ...
Under light-limiting conditions, many ornamental greenhouse-grown plants show undesired morphological characteristics, such as plant elongation (hypocotyl and epicotyl length) and low dry mass, which reduce plant quality. Research has shown that use of plant growth regulators (PGRs) and changes in both light intensity and spectral composition can reduce these undesired characteristics. However, little is known about the role of the combined effects of supplemental lighting and PGRs on the production of ornamental seedlings. The objective of this study was to characterize the combined and independent effects of light intensity, spectral composition, and PGR applications on the greenhouse production of ornamental transplants. Petunia (Petunia × hybrida), geranium (Pelargonium × hortorum), pansy (Viola × wittrockiana) and dianthus (Dianthus chinensis) were grown for 32–42 days under three supplemental light (SL) treatments: 1) high-pressure sodium (HPS), 2) light-emitting diodes (LEDs) with a 6 blue (B):5 green (G):89 red (R) (percent photon flux ratio), and 3) LEDs with 19B:81R (100 μmol m−2 s−1, 18 h photoperiod for all treatments). A control (No SL) was also included. In addition, a portion of plants were also sprayed with the paclobutrazol PGR (PBZ and No PBZ). The synergistic effects of the combination of PBZ and supplemental lighting resulted in the most compact plants, caused by a reduction in plant height by PBZ and an increase in dry mass by SL. However, PBZ reduced shoot dry mass of most plant species and light combinations. Plant compactness was greater under the 6B:5G:89R LED composition for petunia and when combined with PBZ for geranium than for plants under HPS lighting. Root dry mass of petunia, geranium, and pansy plants increased in response to SL compared with no SL by 2.4–5.7-fold. Results from the two LED spectra were unexpected; plants under 6B:5G:89R were more compact (petunia, geranium), had higher anthocyanin concentrations (petunia), were shorter (petunia, pansy, dianthus) and had less leaf area (petunia, pansy, dianthus) than plants in the SL treatment with a higher B and lower G PF (19B:81R). Supplemental lighting and PBZ can be used in conjunction or independently to improve plant morphology. The increased light from SL provided the most benefits by improving dry mass, compactness, and leaf number for most plant species. However, when PBZ was used in combination with SL, plant compactness increased for some species. The spectral composition of SL had an impact on plant growth and morphology, warranting additional research on plant responses to small changes in the spectral composition of SL.
... В настоящее время наметилась тенденция использования более современных и экономичных источников света LED (светодиодных)-облучателей. Они уже пришли в промышленные теплицы и преобразуют электроэнергию в определенный спектр излучения -тот, который нужен растениям больше всего [5,6]. Однако эксперименты с LED-облучателями пока находятся на начальном этапе, и пока незначительное количество культур прошли через стадию первичных исследований. ...
... The use of assimilation light enables yield increase in numerous protected crops and year round high-quality product in regions with insufficient natural light during certain periods of the year (Dueck et al., 2012;Olle and Virsile, 2013;Wojciechowska et al., 2015;Moerkens et al., 2016;Tewolde et al., 2016). These findings have led to a huge increase in area of protected crops equipped with artificial lighting. ...
... Investigations on the placement of light sources within ("interlighting") rather than above the canopy were performed in cucumber (Hovi-Pekkanen and Tahvonen, 2008;Hao et al., 2012), tomato (Dueck et al., 2012;Gómez et al., 2013) as well as for ornamentals (Bergstrand et al., 2015). Interlighting also comprises benefits such as reduced shading and improved microclimate in the canopy, and is already a commercially introduced practice in the production of high-wire crops such as tomato, especially in the Netherlands and in Finland. ...
... Investigations on the placement of light sources within ("interlighting") rather than above the canopy were performed in cucumber (Hovi-Pekkanen and Tahvonen, 2008;Hao et al., 2012), tomato (Dueck et al., 2012;Gómez et al., 2013) as well as for ornamentals (Bergstrand et al., 2015). Interlighting also comprises benefits such as reduced shading and improved microclimate in the canopy, and is already a commercially introduced practice in the production of high-wire crops such as tomato, especially in the Netherlands and in Finland. ...
Horticultural greenhouse production in circumpolar regions (>60°N latitude) is dependent of artificial assimilation lighting, which is a common tool to improve plant performance and consequently profitability of ornamental crops and to secure production of greenhouse vegetables and berries all year round. The anticipated light technology shift in the greenhouse industry not only affects crop growth and development but also quality of the produce. It also influences the interactions with the associated microbiota, i.e., community structure and function as well as establishment, dispersal, survival and propagation of microbial pathogens and biocontrol agents. We present a novel ecological theory and principle based approach for integrated production of greenhouse crops, using improved LED-assisted biocontrol of foliar diseases.
... With respect to the quality of supplemental light, research has shown that at similar PPFD, supplemental PAR from light-emitting diode (LED) technologies have resulted in similar crop production metrics as traditional HPS in greenhouse commodities, such as leafy vegetables [12], fruiting vegetables [13][14][15], ornamentals [16][17][18], and cut flowers [19]. While the capital costs of LED technologies are still considerably higher than HPS, LEDs have many advantages over HPS. ...
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.
... Before the SL treatment started, the plants that were grown in the two compartments showed the same yield, while from the beginning of light treatment until the end of the cycle, the plants grown under LEDs had a higher yield than those without SL (Figure 7). On average, the yield obtained with LEDs was 21.6 kg m −2 , which was lower by about 25.0 kg m −2 as compared to that obtained by Dueck et al. [35] during an experiment conducted in the Netherlands with the same growing cycle and tomato typology as our experiment. If we consider that we started late with SL application, the average yield obtained during our experiment under SL was comparable with the yield obtained in the Netherlands. ...
Supplemental light (SL) is a technique used to increase horticulture yield, especially in northern countries, where the Daily Light Integral (DLI) is a limiting factor during fall and winter, and which could also be used to obtain higher tomato yield at the Mediterranean latitude. In this study, three tomato hybrid (F1) cultivars were grown for year-round production in a commercial semi-closed glasshouse in Southern Italy: two of the cherry fruit-type (‘Juanita’ and ‘Sorentyno’) and one mini plum fruit-type (‘Solarino’). From 120 to 243 days after transplant, light-emitting diode (LED) toplights were used as SL, with a photoperiod of 18 h. The main climatic parameters inside and outside the glasshouse were recorded, and tomato plants’ development and yield were examined. Plants grown with LEDs had longer stems as compared to control treatment (9.53 vs. 8.79 m), a higher stem thickness and yielded more trusses. On average, the yield was 21.7% higher with LEDs. ‘Sorentyno’ was the cultivar with the highest cumulated productivity when it was grown under SL. However, the cultivar with best light use efficiency under LEDs was ‘Solarino’. Therefore, supplemental LED from mid-December until March enhanced tomato growth and yield, opening a favorable scenario for large-scale application of this technology also in the Mediterranean area.
... Lighting with LEDs (light-emitting diodes) in commercial greenhouse production has already been researched in several studies [24,[28][29][30]. At Purdue University, scientists conducted comparative experiments by using LEDs with year-round tomato production in comparison with supplemental light vs. traditional overhead HPS lighting vs. high intensity red and blue LEDs. ...
The amount of energy used in agricultural production, processing and distribution is constantly increasing. During the winter months in the greenhouse production industry, the supplemental lighting required to keep up production levels results in high expenditure. Current technology uses broadband high-pressure sodium (HPS) lamps, which is not the most efficient light source for crop production. Recent breakthroughs in the development of light source technologies have led to new opportunities for the use of sustainable and highly efficient light sources in the form of LEDs (light-emitting diodes) for greenhouse lighting. The aim of the study was to evaluate the efficiency of using photosynthetically active radiation (PAR) light for cucumber yielding, production processes and its influence on the variable costs in the cultivation of cucumbers using three different types of lighting. The research was carried out using three individual greenhouse growing area compartments, whereby the plants contained within were lit using three combinations: 1. HPS standard illumination from top HPS sodium lamps—control, 2. HPS-LED—HPS toplighting and LED interlighting, and 3. LED-LED—100% LED lighting, both toplighting and interlighting with LED. The research was conducted in two independent winter crop cycles. The results of the research conducted indicate that the efficiency of light use was the highest in the LED-LED combination and the lowest in HPS, and the use of supplemental lamp lighting in the LED-LED combination (interlighting and toplighting) gives the most favorable surplus of all the variable costs over the value of production to be obtained. Despite the highest absolute level of variable costs in this type of supplemental lighting, the production value was higher by as much as 32.55% in relation to the HPS combination, which also translated into a gross margin that was higher by about ¾. However, it is worth pointing out that, in the HPS-LED combination, the share of lighting and heating costs in the total value of production was the lowest. It is also a combination currently recommended in the literature as being the most beneficial in greenhouse production.
... The available literature does not provide much information on the hybrid lighting systems for growing tomatoes. In the experiment [13] three lighting systems were compared: 1) HPS lamps, 2) LEDs, and 3) a hybrid system, where the radiation flux was equally divided between HPS lamps and LEDs, with 12 % blue (450 nm) and 88 % red (660 nm) LEDs being used. The irradiation at the top of the plants was set equal. ...
... Greater benefits could be achieved by lighting plants more uniformly along the vertical profile and by increasing the light penetration into the inner part, preventing the lower and inner leaves being below the compensation point (Aikman 1989). Accordingly, interlighting, performed by placing lamps in between of the plant rows, has been applied in several vegetable crops, such as cucumber (Hovi-Pekkanen and Tahvonen 2008;Trouwborst et al. 2010) and tomato (Dueck et al. 2012;Tewolde et al. 2016). This lighting strategy aims to improve the energy budget and the photosynthetic efficiency of whole plants, by enhancing the contribution of lower and inner leaves to carbon gain. ...
We investigated the light response of leaf photosynthesis, stomatal conductance and optical properties in rose plants grown in a glasshouse with bending technique. Leaves were lighted from the adaxial or the abaxial side during measurements, performed in four positions in the upright and bent shoots: top leaves, middle leaves, bottom leaves, and bent shoot leaves. Moreover, the effect of the irradiation on the adaxial or abaxial leaf side on whole canopy photosynthesis was estimated through model simulation. No significant differences were found in light transmission, reflection and absorption of leaves and in photosynthesis light response curves among the four positions. In all the leaf positions, light absorption, stomatal conductance and photosynthesis were higher when leaves were lighted from the adaxial compared with the abaxial side. The model showed that a substantial part of the light absorbed by the crop originated from light reflected from the greenhouse floor, and thus the abaxial leaf properties have impact on whole crop light absorbance and photosynthesis. Simulations were performed for crops with leaf area index (LAI) 1, 2 and 3. Simulation at LAI 1 showed the highest reduction of simulated crop photosynthesis considering abaxial properties; however, to a lesser extent photosynthesis was also reduced at LAI 2 and 3. The overall results showed that the model may be helpful in designing crop systems for improved light utilisation by changing lamp position or level of leaf bending and pruning.
... LEDs rather than HPS) and with equal PAR light level supplied, it is expected that the amount of excessive heat and thus the subsequent heat recovery diminishes. In fact, the crop under such a system may require more thermal energy and, if heat (and ventilation) setpoints are adjusted accordingly to maintain the desired crop temperature (Dueck, Janse, Eveleens, Kempkes, & Marcelis, 2012), this should produce less energy surplus. A scenario with a system to harvest heat excess will also reduce the need for ventilation through both cooling and dehumidification. ...
A greenhouse climate-crop yield model was adapted to include additional climate modification techniques suitable for enabling sustainable greenhouse management at high latitudes. Additions to the model were supplementary lighting, secondary heating and heat harvesting technologies. The model: 1) included the impact of different light sources on greenhouse air temperature and tomato production 2) included a secondary heating system 3) calculated the amount of harvested heat whilst lighting was used. The crop yield model was not modified but it was validated for growing tomato in a semi-closed greenhouse equipped with HPS lamps (top-lights) and LED (inter-lights) in Norway. The combined climate-yield model was validated with data from a commercial greenhouse in Norway. The results showed that the model was able to predict the air temperature with sufficient accuracy during the validation periods with Relative Root Mean Square Error <10%. Tomato yield was accurately simulated in the cases under investigation, yielding a final production difference between 0.7% and 4.3%. Lack of suitable data prevented validation of the heat harvest sub-model, but a scenario is presented calculating the maximum harvestable heat in an illuminated greenhouse. Given the cumulative energy used for heating, the total amount of heating pipe energy which could be fulfilled with the heat harvestable from the greenhouse air was around 50%. Given the overall results, the greenhouse climate(-crop yield) model modified and presented in this study is considered accurate enough to support decisions about investments at farm level and/or evaluate beforehand the possible consequences of environmental policies.
... Intra-canopy lighting stimulates photosynthetic rates in the lower-canopy leaves and prevents their premature senescence (Pettersen et al., 2010;Dueck et al., 2011;Trouwborst et al., 2011;Gomez and Mitchell, 2016). These responses to supplemental inter-lighting might be driven both by the increased light intensity in the lower canopy and by modulation of the light spectrum by the LED lamps. ...
We investigated the effect of supplemental LED inter-lighting (80% red, 20% blue; 70 W m⁻²; light period 04:00–22:00) on the productivity and physiological traits of tomato plants (Flavance F1) grown in an industrial greenhouse with high pressure sodium (HPS) lamps (235 W m⁻², 420 µmol m⁻² s⁻¹ at canopy). Physiological trait measurements included diurnal photosynthesis and fruit relative growth rates, fruit weight at specific positions in the truss, root pressure, xylem sap hormone and ion compositions, and fruit quality. In the control treatment with HPS lamps alone, the ratio of far-red to red light (FR:R) was 1.2 at the top of the canopy and increased to 5.4 at the bottom. The supplemental LED inter-lighting decreased the FR:R ratio at the middle and low positions in the canopy and was associated with greener leaves and higher photosynthetic light use efficiency (PLUE) in the leaves in the lower canopy. The use of LED inter-lighting increased the biomass and yield by increasing the fruit weight and enhancing plant growth. The PLUE of plants receiving supplemental LED light decreased at the end of the light period, indicating that photosynthesis of the supplemented plants at the end of the day might be limited by sink capacity. The supplemental LED lighting increased the size of fruits in the middle and distal positions of the truss, resulting in a more even size for each fruit in the truss. Diurnal analysis of fruit growth showed that fruits grew more quickly during the night on the plants receiving LED light than on unsupplemented control plants. This faster fruit growth during the night was related to an increased root pressure. The LED treatment also increased the xylem levels of the phytohormone jasmonate. Supplemental LED inter-lighting increased tomato fruit weight without affecting the total soluble solid contents in fruits by increasing the total assimilates available for fruit growth and by enhancing root activity through an increase in root pressure and water supply to support fruit growth during the night.
... The benefits of inter-lighting compared to toplighting are not well-established. Dueck et al. (2012) evaluated growth and yield of tomato under 1) toplighting from HPS fixtures, 2) toplighting from LEDs (88%R+12%B; peaks of 660 and 450 nm), 3) toplighting from both HPS fixtures and LEDs, and 4) toplighting from HPS fixtures and inter-lighting from LEDs, all at a supplemental PPFD of 170 µmol m -2 s -1 . Plants grown under the R+B LED toplighting were slightly cooler and required less water, which can be attributed to less radiant heat emitted by the LEDs. ...
... For example, when HPS lamps and LED arrays were used as a top-lighting, there were no differences in fruit dry matter of greenhouse tomatoes between the light treatments but HPS increased TSS (Kowalczyk et al., 2012). The combination of overhead HPS and inter-lighting with LEDs increased crop photosynthesis in both high-wire greenhouse tomatoes (Dueck et al., 2012) and cucumbers (Pettersen et al., 2010;Trouwborst et al., 2010), but showed inconsistent results on fruit yield-it had no effect on tomato yield but an increasing effect on cucumber yield. There were no reports on fruit quality attributes in these studies. ...
Off-season greenhouse tomatoes have a poor reputation relative to their in-season, field-grown counterparts. Previously, we reported that supplemental intracanopy far-red (700‒800 nm, FR) radiation in addition to red (600‒700 nm, R) light with light-emitting diodes (LEDs) significantly decreased fruit water content compared to R LEDs alone and high-pressure sodium (HPS) lamps, the most common supplemental lighting used in commercial greenhouses. We hypothesize that supplemental R+FR LEDs during production improves fruit quality attributes (i.e., physicochemical properties, mineral concentrations, and sensory properties) in greenhouse tomatoes compared to R LEDs and HPS lamps. Both intracanopy LED lights increased fruit yield and biomass compared to HPS lamps. R LEDs increased dry matter ratio and improved overall physicochemical proprieties such as total soluble solids (TSS), titratable acidity (TA), and pH; however, R+FR LEDs had more significant effects on all measured attributes than did R LEDs. Similarly, R LEDs increased potassium, magnesium, and calcium content in whole fruit by 30, 74, and 40% compared to HPS lamps, and the addition of FR to R LEDs further increased sodium (Na) content and concentration. Consumer sensory panelists rated higher for sensory attributes (aroma, sweetness, acidity, and texture) of R+FR LED-supplemented tomatoes on a hedonic scale compared to R LED-supplemented ones. Importantly, HPS lamp-supplemented tomatoes had the least desirable quality attributes even when compared at the same ripe stage as LED-supplemented ones. Energy use efficiency (EUE) was not different between R+FR LEDs and R LEDs, which was 5 times higher than that of HPS lamps. Our results demonstrate for the first time that fruit quality attributes of greenhouse tomatoes can be improved by supplemental intracanopy lighting with R+FR LEDs to a degree that consumer panelists could perceive the differences. Therefore, we conclude that supplemental R+FR LEDs is indispensable for improving fruit quality of greenhouse tomatoes during off-season production.
... This is because LED fixtures typically have lower electric power requirements per unit of growing area (kW · m -2 ) and deliver high light intensities with small amounts of radiant heat delivered to crops, theoretically resulting in significant savings for energy-intensive indoor food production. In addition, by maximizing photon capture efficiency using ''precision'' or ''smart'' lighting'' such as targeted (Poulet et al., 2014), intracanopy (Dueck et al., 2012;G omez and Mitchell, 2016;Massa et al., 2005), or dynamic (Clausen et al., 2015;Pinho et al., 2012;van Iersel, 2017;van Iersel and Gianino, 2017;van Iersel et al., 2016;Weaver et al., 2019) LED lighting, efficiency of production systems can significantly increase. For a comprehensive review of the adoption of LEDs in UA see Gupta (2017). ...
The recent increased market demand for locally grown produce is generating interest in the application of techniques developed for controlled environment agriculture (CEA) to urban agriculture (UA). Controlled environments have great potential to revolutionize urban food systems, as they offer unique opportunities for year-round production, optimizing resource-use efficiency, and for helping to overcome significant challenges associated with the high costs of production in urban settings. For urban growers to benefit from CEA, results from studies evaluating the application of controlled environments for commercial food production should be considered. This review includes a discussion of current and potential applications of CEA for UA, references discussing appropriate methods for selecting and controlling the physical plant production environment, resource management strategies, considerations to improve economic viability, opportunities to address food safety concerns, and the potential social benefits from applying CEA techniques to UA. Author’s viewpoints about the future of CEA for urban food production are presented at the end of this review.
Highlights
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Effects of artificial light sources on fruiting crops can be studied in greenhouses in Norway during winter.
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Regular stem diameter measurement is a method to balance source and sink in tomato plants.
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An installed amount of 242 Watt m-2 HPS top light and a daily light integral (DLI) of 30 mol m-2 day-1 resulted in best light use efficiency in tomato.
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Addition of LED inter-light to HPS top light reduced light use efficiency.
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Winter production using artificial light in Norway can be more energy efficient compared to production under sunlight in southern countries.
One of the challenges for agriculture in the coming years will be producing more food avoiding reducing the nutritional values of fruits and vegetables, sources of nutraceutical compounds. It has been demonstrated that light-emitting diodes (LEDs) used as a supplementary light (SL) technology improve tomato yield in Mediterranean greenhouses, but few data have been reported about SL effects on fruit physio-chemical parameters. In this study, three tomato hybrid (F1) cultivars were grown for year-round production in a commercial semi-closed glasshouse in Southern Italy: red cherry type (“Sorentyno”), red plum type (“Solarino”), and yellow plum type (“Maggino”). From 120 to 243 days after transplant (DAT), Red/White/Blue LEDs were used as SL. The fruits harvested 180 DAT were analyzed and those obtained under LEDs had 3% more dry weight, 15% more total soluble solids, and 16% higher titratable acidity than fruits grown only under natural light. Generally, the antioxidant activity and the mineral profile of the fruits were not negatively influenced by SL. Lycopene content was unchanged and vitamin C content of “Sorentyno” even increased by 15% under LEDs. Overall, LEDs used as SL technology could be one of the tools used by agriculture in Mediterranean basin to produce more food maintaining high quality production.
Herbaceous peony (Paeonia lactiflora) is a flowering species of tremendous commercial potential. Forcing in the greenhouse is used to overcome the problem of the limited flowering period of this species. However, peony growth is constrained by weak light in indoor facilities under winter forcing cultivation. In this study, we used high-pressure sodium (HPS) lamps and light-emitting diodes (LEDs, red: blue = 9:5) as supplemental light sources for the peony cultivar ‘Da Fugui’. This supplemental lighting at an intensity of 200–220 μmol m−2 s−1 provided an additional 5 h of light per day (from 5:00 to 8:00 and from 17:00 to 19:00). The growth and bloom characteristics as well as photosynthesis parameters and products of the peony plants were measured. The results showed that LED treatment increased the net photosynthetic rate (PN) and stomatal conductance (Gs) of leaves at different periods, compared with HPS treatment. By prolonging the photoperiod, both types of light sources significantly increased the flower number, blooming rate, flower diameter and florescence, and improvements were greater with LEDs than with HPS lamps. The findings indicate that LEDs are more suitable for winter supplemental lighting of ‘Da Fugui’ than are HPS lamps.
A system for controlling the lighting up regime is proposed in the article, which gives the opportunity to reduce the cost of consumed electricity. The main element of the proposed control system is a processor, which calculates the necessary power of LED irradiators and the lighting up regimes according to a specially programmed program. For selecting the power and the regime of radiation of a given spectrum, a mathematical model of the geometry of the plant stalk in the process of its growth, obtained from the experimental data, is given. A two-factor experiment was carried out to determine the quantitative effect of the red and blue spectra emitted by LED sources on the geometry of the formed stalk of seed potatoes. The paper presents the results of the experimental studies on a genetically homogeneous material of potatoes grown from meristematic cells, making it possible to obtain reliable responses to different spectral composition of blue and red radiation of LED irradiators. The given system of controlling the lighting up regime allows growing the healthy plants in optimal photosynthesis with the minimal costs of electricity.
Plant responses to the light spectrum under which plants are grown affect their developmental characteristics in a complicated manner. Lamps widely used to provide growth irradiance emit spectra which are very different from natural daylight spectra. Whereas specific responses of plants to a spectrum differing from natural daylight may sometimes be predictable, the overall plant response is generally difficult to predict due to the complicated interaction of the many different responses. So far studies on plant responses to spectra either use no daylight control or, if a natural daylight control is used, it will fluctuate in intensity and spectrum. An artificial solar (AS) spectrum which closely resembles a sunlight spectrum has been engineered, and growth, morphogenesis, and photosynthetic characteristics of cucumber plants grown for 13 d under this spectrum have been compared with their performance under fluorescent tubes (FTs) and a high pressure sodium lamp (HPS). The total dry weight of the AS-grown plants was 2.3 and 1.6 times greater than that of the FT and HPS plants, respectively, and the height of the AS plants was 4-5 times greater. This striking difference appeared to be related to a more efficient light interception by the AS plants, characterized by longer petioles, a greater leaf unfolding rate, and a lower investment in leaf mass relative to leaf area. Photosynthesis per leaf area was not greater for the AS plants. The extreme differences in plant response to the AS spectrum compared with the widely used protected cultivation light sources tested highlights the importance of a more natural spectrum, such as the AS spectrum, if the aim is to produce plants representative of field conditions.
