HPS Lighting Research Articles

Artificial light at night alters foraging behavior of freshwater amphipods depending on the light spectrum and the presence of predation cues

Abstract Artificial light at night (ALAN) is a common anthropogenic disturbance, which alters animal behavior. However, little is known about the impact of the spectral composition of ALAN and co-occurring predation risk on the behavior of aquatic organisms. We experimentally investigated how ALAN of different spectra (cool white LED and HPS light) affects the behavior and foraging of Gammarus jazdzewskii (Amphipoda) on chironomid prey, both as a single stressor and in combination with an olfactory predation cue. Gammarids exposed to ALAN in the absence of predation cues consumed less, compared with darkness, mainly due to their lower activity. Moreover, gammarids showed a stronger response to LED light, spending more time in the shelter and increasing prey handling time in this treatment. The addition of predation cues did not enhance the negative impact of ALAN on the foraging success. Gammarids maintained similar consumption levels as in the ALAN treatment without predation cues and in darkness with predation cues. However, gammarids in LED light altered their behavior in response to predation threat: they decreased prey handling time and consumed prey faster, which may have compensated for the higher food demand in stressful conditions. They also tended to exhibit risky behavior, leaving the shelter and moving towards the lit area, presumably to escape and avoid the combined effects of light and predation cues. Therefore, when assessing the effects of ALAN on organisms, light quality and co-occurring biotic factors should be considered, as predator pressure is common in natural environments.

Nanoparticle Effects on Ice Plant Mineral Accumulation under Different Lighting Conditions and Assessment of Hazard Quotients for Human Health.

Nanotechnologies can improve plant growth, protect it from pathogens, and enrich it with bioactive and mineral substances. In order to fill the lack of knowledge about the combined environmental effects of lighting and nanoparticles (NPs) on plants, this study is designed to investigate how different HPS and LED lighting combined with CuO and ZnO NPs influence the elemental composition of ice plants (Mesembryanthemum crystallinum L.). Plants were grown in hydroponic systems with LED and HPS lighting at 250 ± 5 μmol m-2 s-1 intensity, sprayed with aqueous suspensions of CuO (40 nm, 30 ppm) and ZnO (35-45 nm, 800 ppm) NPs; their elemental composition was measured using an ICP-OES spectrometer and hazard quotients were calculated. LED lighting combined with the application of ZnO NPs significantly affected Zn accumulation in plant leaves. Cu accumulation was higher when plants were treated with CuO NPs and HPS illumination combined. The calculated hazard quotients showed that the limits are not exceeded when applying our selected concentrations and growth conditions on ice plants. In conclusion, ice plants had a more significant positive effect on the accumulation of macro- and microelements under LED lighting than HPS. NPs had the strongest effect on the increase in their respective microelements.

Spotlight on Eupeodes americanus: Oviposition and fertility under HPS- and full spectrum LED-extended photoperiod in northern greenhouses

In northern temperate regions, high-pressure sodium vapor (HPS) or light-emitting diode (LED) lights for supplemental lighting in winter greenhouses are used to extend the photoperiod and increase plant production. These different greenhouse light treatments influence crop pests and their natural enemies. In this study, different greenhouse light treatments were evaluated for their effect on the green peach aphid, Myzus persicae (Sulzer, 1776) (Hemiptera: Aphididae) and its predator the American hoverfly, Eupeodes americanus (Wiedemann, 1830) (Diptera: Syrphidae). In particular, the development of M. persicae and the oviposition and egg hatchability of E. americanus were studied under three light treatments in winter greenhouse: 1) short photoperiod of natural sunlight, and extended photoperiod using either 2) full spectrum LED or 3) HPS lights. The results showed that both extended photoperiod treatments significantly increased M. persicae population growth by 103–130 %, after 12 days compared to short photoperiod of sunlight. Compared to the winter short photoperiod of sunlight, extending the photoperiod did not affect the oviposition of female hoverflies in terms of fecundity, fertility, and niche use (i.e., position of eggs on the plant). Nevertheless, extended photoperiod significantly increased the egg hatchability of E. americanus by 9 % (HPS) and 16 % (LED) compared to short photoperiod of sunlight. This treatment had the highest proportion of unhatched eggs (13 %). Finally, LED lights decreased the proportion of unhatched eggs by 71 % compared to HPS lights. This study, therefore, confirms the potential of the American hoverfly as a biological control agent in winter greenhouses, both with or without artificial light.

Quality and physiological evaluation of tomato subjected to different supplemental lighting systems

Light is a crucial mediator in plants of growth and development, secondary metabolism, and signaling of potentially beneficial phytochemicals. The present study investigated three indoor supplemental light treatments, HPS, LED, and LED+IR, applied during tomato cultivation, in which non-destructive and destructive analyses were performed at two time points to record the physiological responses and effects of these artificial lights on the growth and quality of the produce. An infrared thermometer and thermal cameras were used throughout the experiment to record temperature changes under each growing condition. LED+IR supplemented light showed a decrease in photosynthetic pigments, such as chlorophyll a, b, and carotenoids but induced an increased number of flowers, heavier tomato fruits, enhanced anthocyanins, phenolic index, lipid peroxidation, titratable acidity, and reduced nitrate accumulation. Moreover, higher generated temperatures under LED+IR helped tomato plants to reduce white fly infestation, but suppressed plant height. HPS light performed better than both LED and LED+IR in terms of total sugar accumulation, total carotenoids, water content, plant height, and leaf lipid peroxidation at harvest. Lycopene, ß-carotene, brix index were remarkable under HPS lighting but under the same conditions the number of whiteflies, however, was the highest in HPS among all the tested light treatments. In terms of fruit color analysis, maximum redness (a*), reduced hue angle, and chroma were observed under LED+IR while LED lighting in brightness (L*), and HPS in yellowness (b*) were prominent. However, LED in particular was insufficiently effective in acquiring any possible physiological and qualitative characteristics of tomato plants and fruits for the observed time span of the experiment. Hence, LED+IR has been shown to boost the accumulation of bioactive chemicals, improve fruit quality, promote more rapid and early flowering in tomato plants, and can serve as an efficient replacement for traditional indoor illumination.

Updates on Microgreens Grown under Artificial Lighting: Scientific Advances in the Last Two Decades

Microgreens have a high nutrient density and are beneficial to human health. Even though this class of vegetables have gaining increasing levels of attention in the last year, scientific research on the growth of microgreens in controlled environments under artificial lighting have not been thoroughly characterized. By describing the scientific outputs focused on the impacts of artificial illumination on microgreens, especially from the first two decades of the 21st century, it is therefore possible to detect advancements and research gaps in this research field. This review is divided in two parts: first, a general overview of the scientific production about microgreens; second, a systematic review of scientific studies exploring artificial lighting on the production of microgreens. The overview of scientific production on microgreens and artificial lighting across the Scopus, Web of Science, and Scielo databases, from 2000 to 2021, respectively, indicated three phases, as before 2011 no paper was found: phase 1 (2012 to 2014), six papers; phase 2 (2015 to 2018), fifteen papers; and phase 3 (2019 to 2021), forty-six papers, respectively. Mustard was the most evaluated crop under all production stages. With regard to the second part of this review, studies on artificial lighting with fluorescent lamps (high-pressure sodium light bulbs—HPS), from the supplementation to the replacement of HPS lighting with light emitting diode (LED) lamps, and plant responses with respect to light properties comprise the main works identified. Studies on the distribution of environmental factors under controlled microgreen cultivation present research gaps.

Investigation of different lighting (LED, HPS and FLO) in aquaponics systems for joint production of different plants (Lettuce, Parsley and Cress) and koi carp

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.

Bumblebee pollination activity in a commercial tomato greenhouse during the winter season

Abstract Bumblebee activity interaction with solar irradiation, solar irradiation and HPS lighting irradiation, the HPS effect of photoperiod, day temperature and hive density were assessed with tomato fruit weights in a commercial tomato glass greenhouse in 2020–2021. Pollination activity was measured by observing ten randomly chosen cv. ‘Beorange’ tomato plants and by counting bumblebee bruised tomato flowers. MANOVA was conducted between factors and bee activity, followed by Pearson’s correlation. A Mann-Whitney U test was calculated to determine the significance between tomato flower bruising levels and fruit weights, followed by Cliff’s delta (d). Pollination activity decreased mainly in December and January when solar irradiation decreased to below 110 J cm−2 day−1. Bumblebee activity was significantly affected by solar irradiation with HPS lighting (p<0.001; p<0.01). There was a significant correlation between bumblebee activity and solar irradiation (r= 0.75; p<0.05), and solar irradiation with HPS lighting (r= 0.70; p<0.05). There was no correlation between bumblebee activity and fruit weights (r= −0.20; p<0.05). Bruised flowers had significantly greater fruit weight increases (165.7 g) compared to unbruised flowers (123.4 g) (d= 0.12; p<0.05). Bee activity rates between 60% to 80% can be concluded as an effective rate for tomato growers. Bumblebees need at least 110–154 J cm−2 day−1 of solar irradiation to achieve a high pollination activity rate in temperate climate zones during the winter season.

Artificial light at night (ALAN) affects behaviour, but does not change oxidative status in freshwater shredders

Artificial light at night (ALAN) alters circadian rhythms in animals and therefore can be a source of environmental stress affecting their physiology and behaviour. The impact of ALAN can be related to the increased light level, but also to the spectral composition of night lighting. Previous research showed that many species can be particularly sensitive to the LED light, but it is unclear if they respond to its broad spectrum or specifically to the blue light wavelength. In this study, we tested whether dim ALAN (2 lx) differing in the spectral quality (warm white LED, blue LED, high-pressure sodium HPS light) modifies behaviour and changes oxidative status in two nocturnal freshwater shredder species: Dikerogammarus villosus and Gammarus jazdzewskii (Gammaroidea, Amphipoda). Our experiment revealed that ALAN, irrespective of its spectral quality, did not affect the oxidative stress markers in cells (the level of reactive oxygen species and lipid peroxidation). However, ALAN changed the gammarid behaviour in a species-specific manner, which can potentially reduce the fitness of the shredders. Dikerogammarus villosus avoided all types of light compared to darkness. Therefore, confined to the shelter, D. villosus may have fewer opportunities to forage and/or mate. Gammarus jazdzewskii was sensitive only to the narrow-spectrum blue light, but did not respond to the HPS and white LED light. Avoidance is a typical response of gammarids to natural light, thus the disruption of this behaviour in the presence of common ALAN sources can increase the predation risk in this species. To summarize, behavioural modifications induced by ALAN seem more pronounced than changes in physiology and can constitute the main driver of disturbances in the processing of organic matter in freshwater ecosystems by invertebrate shredders.

Does tomato breeding for improved performance under LED supplemental lighting make sense?

Differences in growth have been reported for tomato under LED compared to HPS light, however, it is not clear if breeding specific for LED supplemental light is worthwhile. Therefore, we derived four recombinant inbred line (RIL) tomato populations from parents with contrasting growth responses to different light spectra. These RIL populations were grown for four weeks under supplemental HPS or 95% red and 5% blue LED light in the greenhouse. For one population we also studied fruit production. Plant height and size of the side shoots of the young plants were strongly reduced under LED supplemental lighting compared to HPS in all populations. The adult plants showed shorter internode lengths, less trusses, less fruits, and lower yield of ripe fruits per plant under LED. However, when the unripe fruits at the last harvest day were included, the difference in yield between HPS and LED disappeared, indicating that the plants under LED light were compacter and slower in development, but in the end produced similar yield. We found numerous QTL, but hardly any of these QTL appeared to be significantly LED-specific. Also, we found very significant genetic effects of maternally inherited plastids and mitochondria, showing the importance of using a parental genotype as mother or as father. However, these effects were very similar between the two light conditions. We conclude that our study does not justify tomato breeding programs that are specifically targeted at 95% red and 5% blue LED supplemental lighting.

Effects of HPS and LED lighting on the growth and the content of selected nutrients in the fruits of Cucumis sativus L.

Effects of HPS and LED lighting on the growth and the content of selected nutrients in the fruits of Cucumis sativus L.

Genetic mapping of the tomato quality traits brix and blossom-end rot under supplemental LED and HPS lighting conditions

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.

Photosynthetic Efficiency and Yield of Cucumber (Cucumis sativus L.) Grown under HPS and LED Lighting in Autumn-Winter Cultivation.

The objective of this study was to evaluate the effect of the supplemental lighting of cucumber with sodium pressure lamps (HPSs) and light-emitting diodes (LEDs) on photosynthetic efficiency and yield in autumn–winter cultivation. Cucumber plants of the ‘Svyatogor’ F1 midi-cucumber parthenocarpic type cultivar were grown on mineral wool mats in three compartments, differing only in the type of light, i.e., (1) HPS top lighting (HPS) in the first compartment, (2) HPS top lighting and LED panel interlighting (HPS + LED) in the second compartment and (3) LED top lighting and inter-row LED panels (LED) in the third compartment. The photosynthetically active radiation was the same in each compartment. The study showed that the highest commercial yields of cucumber could be achieved under LED light (top and inter-row). The chlorophyll content in the leaf blade of younger leaves was higher in plants under LED lighting. This type of lighting also had a positive effect on the gas exchange of plants (net carbon assimilation, stomatal conductance, transpiration). LED and HPS + LED lighting increased the chlorophyll a fluorescence parameters, such as Fs, Fm’ and vitality index (PI), in both younger and older leaves, which also increased the fruit yield in the tested combinations.

Effects of LED and HPS lighting on the growth, seedling morphology and yield of greenhouse tomatoes and cucumbers

In an experiment with tomato and cucumber transplants, light units equipped with purpose-built LED arrays were compared with HPS sodium lamps with a power of 600 W and a voltage of 230 V. For both the LED and HPS lamps, the same PAR radiation level was used at the plant height, which was about 70–80 μmol/m2/s in conditions without daylight. The supplementary lighting was carried out for 8 to 24 hours and was switched on during the day when the solar radiation outside the greenhouse was lower than 200 W/m2. The supplementary lighting with the LED and HPS lamps did not have a significant impact on the growth of the tomato and cucumber seedlings and the fresh and dry mass of the tomato and cucumber plants. The plants grown without the additional artificial lighting were significantly smaller in height, had fewer leaves, a smaller spread and produced lower fresh and dry weights. The tomato and cucumber plants grown under the LED lamps had a higher chlorophyll index than those grown under the HPS lamps and without any lighting. The supplementary lighting with the LED lamps increased the early yield of the tomatoes compared to the HPS and control plants but has no effect on the early yield of the cucumbers. Both the LED and HPS lighting significantly increased the total and marketable yield of the tomatoes and cucumbers.

Light matters: Effect of light spectra on cannabinoid profile and plant development of medical cannabis (Cannabis sativa L.)

Light is a key factor affecting plant growth, metabolism and function. Metabolic processes in plants are sensitive to the ratio of Blue:Red light, and there is an increasing awareness that the response to the ratio of these monochromatic lights may vary under exposure to a wider range of the spectrum, such as white light. Due to the potential for regulation of the therapeutic chemical profile and plant development, this issue is of growing interest for the cannabis (Cannabis sativa L.) industry that uses photosynthetic light extensively. Cannabis is a medicinal plant treasured for its secondary metabolites, especially cannabinoids, the unique biologically active compounds in the plant that are considered to be affected by light spectra. In this study we evaluated the hypothesis that the ratio of Blue:Red light affects cannabinoid metabolism, and that plant growth and secondary metabolism is intensified under a full spectrum with similar Blue:Red ratio. Our results point to several spectra specific reactions and some cultivar dependent responses to light spectrum. i. Yield quantity: The highest inflorescence yields were obtained when the spectrum was restricted to the red and blue range at the ratio of 1:1, and in two of the three varieties tested a ratio of 1:4 Blue:Red light had similar results. White light with Blue:Red ratio of 1:1 had the lowest yield. ii. The chemical profile was also affected by the light spectrum, and CBGA, the primary cannabinoid and a precursor for most other cannabinoids, demonstrated the highest response. CBGA accumulation was stimulated by blue-rich light as compared with far-red rich HPS light. The major cannabinoids CBDA, THCA and CBCA were also affected by light quality, and the response was cultivar specific and less pronounced than for CBGA. iii. Plant morphology: Blue light was most inductive for maintaining compact plants, more so than Red:Far-Red ratio. Our results repute the hypothesis that full spectrum improves inflorescence yield compared with Blue:Red light, but support the hypothesis that light spectrum influences plant development and the cannabinoid profile, which could be used to fine-tune cannabis and cannabinoid production.

Lighting systems and strategies compared in an optimally controlled greenhouse

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.

ПРОДУКТИВНОСТЬ МИКРОВОДОРОСЛИ CHLORELLA SOROKINIANA ПРИ ВЫРАЩИВАНИИ НА КУРИНОМ ПОМЁТЕ В РАЗНЫХ УСЛОВИЯХ ОСВЕЩЕНИЯ

The production of microalgae biomass on agricultural waste has a high potential, which is associated both with solving a number of environmental problems and also with obtaining a commercial effect. The purpose of the research is to determine the production characteristics of Chlorella sorokiniana microalgae when grown under different light conditions on a nutrient medium prepared on the basis of chicken manure. The research was carried out in the laboratories of the Federal Agricultural Kursk Research Center in 2020–2021. The object of the study is a culture of microalgae Chlorella sorokiniana (IPPAS C-1). Chicken manure in terms of dry weight contained 3.82 % of total nitrogen, 1.93 % – phosphorus, 55.26 % – organic matter. The toxic elements were within acceptable limits. A distinctive feature of the method of preparing a nutrient medium based on manure was its use without preliminary fermentation at a dose of 7 g/l. Photobioreactors with a volume of 5 liters of closed type with constant artificial lighting and 20 liters of open type with natural lighting were used for work. The culture layer for all variants of the experiment was 0.15 m. Artificial lighting was represented by HPS 150 W and energy-saving LED Aquael 10 W lamps. Illumination under artificial lighting was 20 and 40 klx, under natural lighting – 36 and 70 klx. When comparing different lighting sources, it was found that the use of a nutrient medium based on chicken manure made it possible to obtain a culture of Chlorella sorokiniana with a cell density from 38.67 to 62.66 million ml-1 under LED lighting, from 43.67 to 76.67 million ml-1 under HPS lighting and from 17.33 to 41.33 million ml-1 under natural lighting. Considering the three types of lighting, it should be noted that the most optimal way of Chlorella sorokiniana cultivation is on chicken manure under natural and LED lighting. Variants with a HPS lighting system were more energy-intensive even though they had a higher cell density.

Mineral nutrients needs of cucumber and its yield in protected winter cultivation, with HPS and LED supplementary lighting

The objective of the study was to evaluate yield, mineral nutrients uptake and nutrient demands of cucumber plants in winter cultivation with HPS and LED supplementary lighting. The experiment was carried out in the three variants: 1) HPS - top light only; 2) HPS + LED - top light + 2 lines of LED inter-row light; 3) LED + LED - top LED + 2-line LED inter-row light. In these variants the same PAR intensity level, of about 320 μmol m−2 s−1 (PPFD), was provided. Midi-cucumber parthenocarpic cultivar ‘Svyatogor’ F1, of high shade tolerance and 18–22 cm fruit lenght, was grown for 17 weeks during winter, in mineral-rock slabs. The plants were trained on a single stem up a string, according to the ‘high wire system’ method. Number and weight of every-day harvested fruit were determined. On the basis of monitoring, content of macro- and micro-elements in drip and drain solutions that was undertaken during every two-week period and constant monitoring of total daily drip irrigation quantity with nutrient solution per one plant, as well as total daily drain of the nutrient solution, the daily uptake of nutrient solutions and nutrients per one plant was calculated. The nutrient status of the plants was determined by leaf samples analysis performed for the younger, upper 3rd–5th leaves, as well as for the older, 10th–12th, lower leaves. Cucumber plants were characterized by stable yield and showed high fruit yield of very good quality. The highest yield was found for the plants grown with supplementary lighting with LED + LED. Leaves from the plants grown with the standard HPS top lighting showed faster senescence than the leaves of the plants grown with inter-row lighting. This is evidenced by a higher concentration of Ca, Mg, S, Mn and B ions, together with a lower concentration of K ions, in 10th–12th leaves in the plants grown with the standard HPS top lighting, compared with the plants grown with the HPS + LED lighting, as well as with the LED + LED lighting. The plants grown with the inter-row lighting showed a higher nutritional demands than the plants grown with the standard HPS top lighting. Parallelly used LED top lighting resulted in a higher and more stable yield, compared to standard HPS lighting conditions.

Convex parameter estimator for grey-box models, applied to characterise heat flows in greenhouses

An algorithm is presented to identify model parameters in grey-box models. The solver is convex, so the global optimum is guaranteed. The method is applied to estimate bulk transfer coefficients in greenhouses from easily monitored data. This model covers the most important processes, such as conduction losses to the environment, heat exchange with neighbouring compartments, heating from the sun and lighting installations, and ventilation losses. Screen positions are also included in the model. Each process is parameterised, so that the specific situation of each greenhouse can be identified. Greenhouse experiments are often repeated in the same greenhouse or performed in parallel. If some model parameters are assumed to remain identical in these experiments, this can be incorporated in the optimiser making it more robust. The estimator is exemplified using measurements from two compartments in a greenhouse; one equipped with LED lighting, the other equipped with HPS lighting. It showed that effective conduction parameters for the greenhouse and screens were similar to values found in literature (5.8 and 5 W m−2 K−1, respectively). The model also predicted that both lighting systems provide the same amount of sensible heat at the height of the plants, despite the HPS system consuming 43% more energy. A vertical temperature measurement confirmed that both lighting systems produced the same amount of heat at the height of the plants. The LED system dispersed heat more evenly over height, while the HPS system heated the upper layers more.

Influence of leaf temperature and blue light on the accumulation of rosmarinic acid and other phenolic compounds in Plectranthus scutellarioides (L.)

In this study, the influence of different lamp types on physiology and secondary metabolites of Plectranthus scutellarioides (Solenostemon scutellarioides, Coleus blumei) was examined. The following four lamp systems were tested: a new microwave plasma lamp (MPL) emitting artificial sunlight, a commercial high-pressure sodium lamp (HPS), a ceramic metal halide lamp (CDM), and light-emitting diodes (LEDs). The lamps differed not only in the spectral properties of the emitted light but also in the emission of infrared radiation. The aim of this study was to investigate both the influence of the spectral quality and the influence of the leaf temperature from four different lamp systems on morphology and secondary metabolites in P. scutellarioides. Total phenolic compounds were quantified with colorimetric methods. For detailed description of the phenolic compounds, qualitative and quantitative analysis of selected phenolic compounds were performed by HPLC.Stem elongation was increased in plants grown with MPL and LED light, which was attributed to the higher amount of far-red light in the emission spectra. On the other hand, higher infrared radiation from MPL and HPS lamps led to increased leaf temperatures compared to plants grown with LED or CDM light, resulting in faster plant development indicated by greater leaf pair formation. In addition to rosmarinic acid (RA), which is typical for members of the family Lamiaceae, luteolin and apigenin glycosides were detected by mass spectrometry. The results demonstrated that P. scutellarioides leaves contained three acylated cyanidin diglycosides, one of them containing just a coumaroyl residue, the other two containing one and two additional malonyl residues, whereby malonylated compounds appeared in higher quantities. Leaves grown with LED and CDM light contained the highest amount of RA and flavone glycosides per dry weight, which was attributed to a lower leaf temperature compared to leaves developed under MPL or HPS light. Further, an increased blue light content in the emission spectra led to thicker leaves and consequently to a higher accumulation of secondary metabolites per leaf area.

Effect of planting time and supplemental irradiation on growth and flowering of Lachenalia 'Romaud'

Growth and flowering of lachenalia ‘Romaud’ was studied with reference to its commercial potential as pot plant and the need to obtain flowering plants at a specific time. The experiment was carried out in a heated glasshouse. Lachenalia bulbs were planted in November, December, January and February. The plants were exposed to two lighting regimes, natural lighting and natural lighting with supplemental irradiation (HPS lamps). The later the planting date was, the faster the bulbs flowered, and they produced thicker inflorescence stems with greater number of florets. Depending on the bulb planting date and light conditions, the plants flowered from February to May. The leaves obtained from the bulbs planted in November and December were longer than those produced by the bulbs planted in January and February. Compared with control, supplemental irradiation accelerated flowering by 10–13 days and positively affected plant features by promoting the growth of thicker inflorescence stems with more abundant and longer florets. The leaves of irradiated bulbs were shorter (apart from the bulbs planted in February) and were characterised by a higher content of chlorophyll a, chlorophyll a + b and carotenoids as compared with control. Plants grown under HPS light also had the higher dry weight of bulbs, leaves and stems.