High-pressure Sodium Lamps Research Articles

Balancing Yield and Sustainability: A Comparative Analysis of Supplemental Lighting in Commercial-Scale Cucumber Cultivation

Lighting is a fundamental driver of plant productivity in controlled-environment agriculture (CEA), directly affecting physiological processes, resource efficiency, and sustainability. This study evaluates the effects of distinct lighting systems, industrial Light-Emitting Diodes (iLEDs), horticultural LEDs (hLEDs), high-pressure sodium (HPS) lamps, and controls (no supplemental light), each providing unique light spectra, on cucumber (Cucumis sativus L.) growth, physiology, and environmental impact under a controlled light intensity of 250 µmol m−2 s−1 in a commercial CEA setup. The results indicated that iLEDs enhance intrinsic water use efficiency (35.65 µmol CO2/mol H2O) and reduce transpiration, reflecting superior physiological resource use. Electrophysiological measurements indicated significantly more stable stress responses in plants subjected to iLEDs and hLEDs as compared to HPS and control treatments, indicating the effectiveness of LED light spectra in mitigating stress-related physiological impacts. Furthermore, compact growth and shorter stem internodes were observed under iLEDs as well as hLEDs, highlighting the spectral effects on photomorphogenesis, likely caused by a balanced light spectrum. HPS lighting achieved the highest yield (42.86 kg m−2) but at a significant environmental cost, with 342.65 kg CO2e m−2 emissions compared to 204.29 kg CO2e m−2 for iLEDs, with competitive yield of 38.84 kg m−2. Economic analysis revealed that iLEDs also offered the most cost-effective solution due to lower energy consumption and extended lifespan. This study focused on the interaction between light spectra, photosynthetic performance, stress resilience, and resource efficiency, advancing sustainable strategies for energy-efficient food production in CEA systems.

Effects of Adjusted Light Levels on Plant Growth and Flowering Characteristics of Oncidesa Cultivars

The aim of this study was to evaluate the growth and flowering characteristics of three Oncidesa cultivars under four distinct canopy treatments in a greenhouse environment. The control canopy treatment (canopy D) involved covering the greenhouse with black shade nets to reduce natural light penetration. Canopy B included black shade nets in combination with a transparent plastic screen on the sides to further modify the light conditions. Additionally, two other treatments were applied: black shade nets with (canopy A) or without (canopy C) plastic sheeting, supplemented with daily lighting from high-pressure sodium lamps. Ten horticultural traits were measured to assess the impact of these canopy treatments on different cultivars at various growth stages. The results show that canopy treatments significantly affected all the measured traits of the Oncidesa cultivars, except for leaf width. Apollo plants treated under canopy A exhibited longer and thicker pseudobulbs, wider leaves, higher chlorophyll content, and a greater number of branches and florets compared to Honey Angel and Golden Star. Plants under canopy C showed superior growth traits across all cultivars, while those under canopies A and D exhibited better flowering quality. These findings suggest that different canopy treatments had varying effects on the growth and flowering traits of Oncidesa cultivars, with each cultivar showing distinct adaptability to specific canopy conditions.

Evaluating the effect of supplementary lighting on the growth and physiological activity of roses during winter by plant-induced electrical signal

ABSTRACT Limited light intensity and low temperature in winter lead to various challenges such as reduction in growth, yield and quality of cultivated roses, which can be complemented by artificial supplementary lights. This study aims to evaluate the effect of different supplementary lights, including metal-halide (MH), metal-halide+high-pressure sodium lamp (MH + HPS) and high-pressure sodium lamp (HPS) on the growth characteristics of cultivated roses in winter. Compared to individual light, the results demonstrated that combined supplementary lights (MH + HPS) increased stem diameter, number of leaves and flower diameter of cultivated roses. The height, leaf length, leaf width, number of petals, chlorophyll content and chlorophyll fluorescence (Fv/Fm) of roses grown in different supplementary lights were not significantly affected. In all the three treatment areas, photosynthetic photon flux density (PPFD) and temperature at night were higher in the MH + HPS area, followed by the HPS and MH areas. The plant-induced electrical signal (PIES) of roses cultivated under MH + HPS light indicated higher water and nutrient uptake than other treatments, which was positively associated with rose growth, but the difference was insignificant. Principal component analysis (PCA) revealed that the growth parameters of roses were mainly associated with MH + HPS supplementary light. Therefore, combined supplementary light was beneficial to improve the growth and quality of cultivated roses.

Autonomous Street Lighting System based on Solar Energy and LEDs

This paper introduces a solar-powered autonomous street lighting system designed primarily for areas without access to the grid, such as rural roads and intersections. It utilizes solar panels as the primary energy source, with batteries serving as backup, and employs light-emitting diodes (LEDs) for illumination. The proposed system is optimized for efficiency by employing direct current (DC) power at all stages. To replace a 70W high-pressure sodium (HPS) lamp, an LED fixture design is discussed, considering human scotopic vision. Experimental outcomes for the LED driver and battery charger are provided, demonstrating features such as maximum power point tracking (MPPT), constant current, and constant voltage modes. The system ensures MPPT under varying solar irradiance and temperature conditions by analyzing the battery charger input impedance.

The power of spectrally enhanced artificial night-time lights data: Assessing NTL risks along the urban-natural interface

Artificial night-time lights (NTL) have long been known for their adverse effects on humans and the environment. Recent studies report that the severity of NTL impact on organisms is associated not only with its intensity but also a spectrum. The spectral resolution of freely available satellite NTL data is restricted to red, green, and blue sub-spectra, which are significantly wider than the ranges of vulnerability, reported by laboratory studies for various species. The present study is the first attempt to overlap spectrum-specific NTL data, describing the intensities of light emitted by different lamp types with relatively narrow emission peaks, with the sites where species vulnerable to specific NTL sub-spectra were detected. We overlap those light intensity maps with increasingly detailed maps of natural areas located along the urban-natural interface of the Haifa region. We analyze light pollution in the ecological corridors, which host numerous species with different, but unknown, spectrum-specific effects of NTL (a coarse-level analysis), and in the sites of several species, with either known or unknown spectrum-specific effects of NTL (a fine-level analysis). We show that a considerable part of the ecological corridors is polluted by metal halide and high-pressure sodium lamps which may negatively influence plants, bees, sea turtles, birds, and mammals. One habitat site of the Near Eastern fire salamander (Salamandra infraimmaculata) is polluted by lamps with green-light emission peaks which may explain the low reproductive success of this population. Despite the study limitations, related to the region-specific NTL data of spectrum-specific resolution and scarcity of evidence about the spectrum-specific NTL harmful effects on organisms, we believe that the obtained results would contribute to the elaboration of more informed fine-tuned artificial lighting policies which would diminish the burden of urban built-up zones on their neighboring natural areas.

LED streetlamps alter tree architecture, downregulate the photosynthetic process and alter the sugar metabolism of Populus alba L.

The escalating issue of light pollution in urban environments poses multifaceted challenges, affecting not only the nocturnal sky but also exerting intricate influences on plant physiology. This study delves into the physiological responses of an urban ornamental tree, Populus alba L. clone DI-1, to varying intensities of streetlamp LED night lighting (NL), a shift from traditional High-Pressure Sodium lamps. The investigation “sheds light” on the molecular pathways underlying observed physiological regulations, aiming to offer a comprehensive understanding of the manifold effects of NL on this tree species. NL altered tree architecture, i.e. increased branch length and diameters, underscoring the dynamic response of trees to nocturnal artificial lighting conditions. Regarding tree physiology, the NL-triggered net CO2 assimilation (Pn) during the night resulted in limitations in stomatal conductance during daylight hours. This led to a reduction in Pn, particularly during dawn, hindering the quantum yield for the reduction of end acceptors of PSI. Changes in chlorophyll a-to-b proportion and overall concentration, electron transport chain, and gene expression further highlight the intricate interplay between NL and plant metabolic regulation. Notably, the increased gene expression of sugar transporters in both NL trees suggested a responsive shift in sugar and starch metabolism. This was reflected in the absence of a starch accumulation during daylight hours in NL leaves. The study emphasizes the need for a holistic approach to urban lighting, considering its profound impact on photosynthesizing citizens. These findings highlight the pressing need for the development of innovative lighting spectra with reduced impact on plant physio-chemistry while ensuring visibility for citizen safety.

Growth, leaf anatomy, and photosynthesis of cotton (Gossypium hirsutum L.) seedlings in response to four light-emitting diodes and high pressure sodium lamp

BackgroundLight is a critical factor in plant growth and development, particularly in controlled environments. Light-emitting diodes (LEDs) have become a reliable alternative to conventional high pressure sodium (HSP) lamps because they are more efficient and versatile in light sources. In contrast to well-known specialized LED light spectra for vegetables, the appropriate LED lights for crops such as cotton remain unknown.ResultsIn this growth chamber study, we selected and compared four LED lights with varying percentages (26.44%–68.68%) of red light (R, 600–700 nm), combined with other lights, for their effects on growth, leaf anatomy, and photosynthesis of cotton seedlings, using HSP lamp as a control. The total photosynthetic photon flux density (PPFD) was (215 ± 2) μmol·m−2·s−1 for all LEDs and HSP lamp. The results showed significant differences in all tested parameters among lights, and the percentage of far red (FR, 701–780 nm) within the range of 3.03%–11.86% was positively correlated with plant growth (characterized by leaf number and area, plant height, stem diameter, and total biomass), palisade layer thickness, photosynthesis rate (Pn), and stomatal conductance (Gs). The ratio of R/FR (4.445–11.497) negatively influenced the growth of cotton seedlings, and blue light (B) suppressed stem elongation but increased palisade cell length, chlorophyll content, and Pn.ConclusionThe LED 2 was superior to other LED lights and HSP lamp. It had the highest ratio of FR within the total PPFD (11.86%) and the lowest ratio of R/FR (4.445). LED 2 may therefore be used to replace HPS lamp under controlled environments for the study of cotton at the seedling stage.

Neutral Currents in Large Public Lighting Networks

The modern large public lighting networks are characterized by two major aspects that rise problems from both power quality and neutral current point of view in low voltage wye-connected three-phase electrical systems: (i) the supply system is unbalanced loaded; (ii) the presence of discharge sources. It is important to underline that nowadays,these aspects are not taken into account in the proper sizing of neutral conductors. The paper presents a simplified but enough accurate methodology to estimate the RMS value of neutral currents in lighting networks. The theoretical relationships are illustrated for a three-phase public lighting network that contains high pressure sodium lamps.

Nutrient Solution Application of a Calcium-mobilizing Biostimulant Mitigates Tipburn without Decreasing Biomass of Greenhouse Hydroponic Lettuce

Lettuce tipburn is a physiological disorder characterized by marginal necrosis and curling of inner, younger leaves caused by localized calcium deficiency, especially in low evapotranspiration environments that restrict mass flow and thus calcium mobility. Severe tipburn negatively affects the marketability and quality of greenhouse-grown hydroponic lettuce. We aimed to assess the effectiveness of a chemical-based, calcium-mobilizing biostimulant for mitigating lettuce tipburn when applied in hydroponic nutrient solutions. Butterhead lettuce (Lactuca sativa ‘Rex’) was grown indoors under warm-white light-emitting diodes at a mean photosynthetic photon flux density of 300 μmol⋅m−2⋅s−1 for 11 days. Subsequently, we transplanted seedlings into deep-water-culture hydroponic trays in a greenhouse at an air temperature of 24.6 ± 1.2 °C, relative humidity of 76.2% ± 7.4%, and 20-hour photoperiod with supplemental lighting from high-pressure sodium lamps. The plants were grown in nutrient solutions with and without the biostimulant codenamed CC US-2105 at two concentrations (22 and 220 μL⋅L−1). Data were collected from plant samples at three harvests at 14, 21, and 28 days after transplant (DAT). At 14 DAT, there was no tipburn under any treatments. Compared with the control, the biostimulant at 22 μL⋅L−1 increased shoot dry mass by 31%. At 21 DAT, the biostimulant at 220 μL⋅L−1 eliminated tipburn, and the biostimulant increased shoot fresh weight by 28%, irrespective of the concentration. At 28 DAT, despite sufficient calcium in the whole plant and the remaining nutrient solution, severe tipburn still occurred in plants that did not receive the biostimulant (control). Compared with the control, the biostimulant at the higher concentration of 220 μL⋅L−1 decreased the tipburn rating by 88% and the number of leaves with tipburn by 85%, increased the plant diameter by 11%, increased the total leaf number by six, and accumulated higher levels of manganese and zinc. In contrast, these parameters remained unaffected at the lower biostimulant concentration of 22 μL⋅L−1. At 28 DAT, shoot biomass was unaffected by the biostimulant. In conclusion, the calcium-mobilizing biostimulant is an effective strategy to mitigate hydroponic lettuce tipburn without decreasing biomass accumulation in greenhouse conditions.

The role of supplemental lighting during late fall and winter on photosynthetic and non-photosynthetic pigments biosynthesis of cut rose flower (Rosa hybrida cv. ‘Dolce Vita’)

ABSTRACT Low levels of natural light within the late fall and winter periods are main restricting factors for greenhouse-cut rose flower production in northern countries. Here, the effects of supplemental lighting on photosynthetic and non-photosynthetic pigments and the morphological response of cut rose flower cv. ‘Dolce Vita’ were investigated. Four different supplemental lighting regimes, including 85, 170, 255, and 340 μmol·m−2·s−1 PPFD using a high-pressure sodium lamp for a six-hour day extension started at sunset were applied to rose plants during late fall and winter. With increasing light intensity to 255 μmol·m−2·s−1 PPFD, the content of chlorophyll a, total chlorophyll, carotenoid content, and the ratio of chlorophylls a/b as well as amount of anthocyanins greatly improved. The highest phenol content and total antioxidant capacity was observed in 170 μmol·m−2·s−1 PPFD. Moreover, extending of daylength by light intensity of 255 μmol·m−2·s−1 PPFD had a significant affirmative effect on traits of growth, including flower stem length (P < 0.01), leaf number (P < 0.05), renewal bud formation (P < 0.05), time of harvesting (P < 0.05), and vase life of cut flowers (P < 0.01). Considering physiological and morphological improvement, extending of daylength from 10-h to 16-h by supplemental light of 255 μmol·m−2·s−1 PPFD would be the best choice to cultivate cut rose flower cv. ‘Dolce Vita’.

Evaporated Chalcopyrite Thin Films for Indoor Photovoltaic Applications

The feasibility of capturing indoor artificial light using chalcopyrite photovoltaic absorbers has been analyzed. For this purpose, various chalcopyrite compounds (CuInSe2, CuInS2 and CuGaS2) were prepared by evaporation and then measured to obtain their main structural, morphological and optical characteristics. On the other hand, several artificial light sources were selected (incandescent, halogen, fluorescent, high-pressure sodium, metal halide and LED lamps) and represented by their respective spectral radiance. The absorption characteristics of CuInSe2 and CuInS2 are optimal for collecting light from fluorescent lamps and warm or cool white LEDs, requiring only a small film thickness of about 0.6 μm to capture 90-100% of the light radiance. Otherwise, the efficiency of CuGaS2 is found to increase as the color temperature of the LED lamp increases, being always lower and more dependent on the film thickness than for the other evaporated compounds. The worst performances (collection of less than 50% of the light radiance) correspond to incandescent and halogen lamps, which have a significant emission in the infrared region outside the absorption range of the evaporated chalcopyrite films. These results provide guidelines for the design of chalcopyrite-based photovoltaic devices suitable for operation under different indoor lighting conditions.

Better red than dead: Plasticine moths are attacked less under HPS streetlights than LEDs

Anthropogenic light at night is growing exponentially while many insect populations are in decline. Many nocturnal insects provide numerous ecosystem services and are attracted to anthropogenic lights at night resulting in decreased fitness, greater mortality and population declines. During twilight and night, moths are depredated by bats and birds, both of which use vision, among other strategies, to detect and prey upon moths. The visual detection of moths by predators is dependent upon the light environment illuminating the moth's body. Effects of anthropogenic light at night can differ drastically with the color (spectral composition) and intensity of light. Currently, high pressure sodium lamps (HPS) and light emitting diodes (LEDs) are common municipal light sources, and these lights differ spectrally, thus altering the visual scene. Most LEDs are broadband (i.e., white) whereas HPS are long wavelength dominant (i.e., amber); both of these light types can alter color perception of prey. To test if moths are more likely to survive under HPS lighting than LEDs and non-lit poles, we used plasticine clay models. Visual model analyses reveal that HPS lamps rendered moths more cryptic against their background than LEDs or ambient urban lighting, albeit with small differences in contrast that may not be biologically relevant. These results indicate that HPS lighting is the most insect-friendly lighting when considering depredation on insects in comparison to LED.

Evaluation of LED Luminaire Utilizatıon in Road Lighting Installations in Terms of Electrical Energy Qualty

In this study, three roads with M2 lighting class, which are currently illuminated with high pressure sodium lamp (HPSL) luminaires, in three different provinces of Turkey (Samsun, Trabzon, Denizli) were selected as pilot roads. The lighting quality values of the existing HPSL luminaire installations and the new LED installations are measured by a luminance meter and electrical energy quality values like the active, reactive power, current, voltage and the power factor, odd current and voltage harmonics, and the total harmonic distortion values of the current and voltage are measured with an energy analyser. The measurement results of the illumination and electrical quality values determined for the luminaires with HPLS and LED after conversion. Evaluations were made for 100 % working status of LED luminaires, M2, M3, and M4 lighting classes depending on the automation system.

Intumescence Response by Tomato Plants Grown in a Greenhouse or Indoors Using Two Types of Soilless Culture Systems

The main objective of this study was to characterize intumescence injury of three susceptible tomato cultivars grown in a greenhouse or indoors using two types of soilless culture systems. Plants of cultivars Maxifort, Camaro, and Patio were grown in either an indoor environment with broadband white and red light-emitting diode (LED) fixtures providing a daily light integral (DLI) of 12.7 mol·m−2·day−1 [photosynthetic photon flux density (PPFD) of 220 ± 3 µmol·m−2·s−1 for 16 h·d−1] or in a glass-glazed greenhouse with supplemental lighting provided by high-pressure sodium lamps that delivered a PPFD of ∼150 µmol·m−2·s−1. Plants were grown using deep-water culture hydroponic systems or containers with a peat-based substrate. The growing environment had a larger effect on intumescence incidence and severity than the growing system, likely due to differences in ultraviolet radiation (100 to 400 nm), but other factors such as day/night temperature and relative humidity (RH), could have affected the response. Across cultivars, the probability of developing intumescence was higher indoors (≥91%) than in the greenhouse. Indoor-grown plants also developed symptoms of the disorder from 2 to 6 days earlier than those in the greenhouse. Similarly, intumescence incidence was higher in plants from all cultivars grown indoors than in the greenhouse, but differences between the two environments were generally greater for Patio and Camaro than for Maxifort, which was the most susceptible cultivar. Greenhouse conditions were more conducive to active plant growth. For example, plants in the greenhouse were more than 2 times taller and had at least 12 times greater leaf area than those indoors, which resulted in large differences in shoot dry mass. However, environmental effects on intumescence response also contributed to differences in growth, as plants that were most affected by the disorder experienced severe leaf abscission and/or senescence. Our overall findings show that intumescence is greatly affected by the production environment, but injuries are likely to change based on genetic susceptibility.

Vegetation Indices for Early Grey Mould Detection in Lettuce Grown under Different Lighting Conditions.

Early detection of pathogenic fungi in controlled environment areas can prevent major food production losses. Grey mould caused by Botrytis cinerea is often detected as an infection on lettuce. This paper explores the use of vegetation indices for early detection and monitoring of grey mould on lettuce under different lighting conditions in controlled environment chambers. The aim was focused on the potential of using vegetation indices for the early detection of grey mould and on evaluating their changes during disease development in lettuce grown under different lighting conditions. The experiment took place in controlled environment chambers, where day/night temperatures were 21 ± 2/17 ± 2 °C, a 16 h photoperiod was established, and relative humidity was 70 ± 10% under different lighting conditions: high-pressure sodium (HPS) and light-emitting diode (LED) lamps. Lettuces were inoculated by 7-day-old fungus Botrytis cinerea isolate at the BBCH 21. As a control, non-inoculated lettuces were grown under HPS and LEDs (non-inoculated). Then, the following were evaluated: Anthocyanin Reflectance Index 2 (ARI2); Carotenoid Reflectance Index 2 (CRI2); Structure Intensive Pigment Index (SIPI); Flavanol Reflectance Index (FRI); Greenness (G); Greenness 2 (G2); Redness (R); Blue (B); Blue Green Index 2 (BGI2); Browning Index 2 (BRI2); Lichtenthaler Index 1 (LIC1); Pigment Specific Simple Ratio (PSSRa and PSSRb); Gitelson and Merzlyak (GM1 and GM2); Zarco Tejada-Miller Index (ZMI); Normalized Difference Vegetation Index (NDVI); Simple Ratio (SR); Red-Eye Vegetation Stress Index (RVSI); Photochemical Reflectance Index (PRI); Photochemical Reflectance Index 515 (PRI515); Water Band Index (WBI); specific disease index for individual study (fD); Healthy Index (HI); Plant Senescence Reflectance (PSRI); Vogelmann Red Edge Index (VREI1); Red Edge Normalized Difference Vegetation Index (RENDVI); and Modified Red Edge Simple Ratio (MRESRI). Our results showed that the PSRI and fD vegetation indices significantly detected grey mould on lettuce grown under both lighting systems (HPS and LEDs) the day after inoculation. The results conclusively affirmed that NDVI, PSRI, HI, fD, WBI, RVSI, PRI, PRI515, CRI2, SIPI, chlorophyll index PSSRb, and coloration index B were identified as the best indicators for Botrytis cinerea infection on green-leaf lettuce (Lactuca sativa L. cv Little Gem) at the early stage of inoculated lettuce's antioxidative response against grey mould with a significant increase in chlorophyll indices.

Application timing and duration of LED and HPS supplements differentially influence yield, nutrient bioaccumulation, and light use efficiency of greenhouse basil across seasons.

Three primary factors that impact plant growth and development are light quantity, quality, and duration. Commercial growers can manipulate these parameters using light-emitting diodes (LEDs) to optimize biomass yield and plant quality. There is significant potential to synergize supplemental lighting (SL) parameters with seasonal variation of ambient sunlight to optimize crop light use efficiency (LUE), which could increase biomass while reducing SL electricity costs. To determine the best lighting characteristics and durations for different crops, particularly for enhancing the yield and nutritional quality of high-value specialty crops produced in greenhouses during the winter, a thorough efficacy comparison of progressive incremental daily light integrals (DLIs) using LED and high-pressure sodium (HPS) sources is required. The purpose of this study was to compare the effects of differential application timing and DLIs of supplemental blue (B)/red (R) narrowband wavelengths from LED lighting systems and HPS lamps on greenhouse hydroponic basil (Ocimum basilicum var. 'Genovese') production. We assessed edible biomass, nutrient bioaccumulation, and LUE. Nine light treatments included: one non-supplemented natural light (NL) control, two end-of-day (EOD) HPS treatments applied for 6h and 12h, five EOD 20B/80R LED treatments applied for 3h, 6h, 9h, 12h, 18h, and one continuous LED treatment (24h). Each SL treatment provided 100 µmol·m-2·s-1. The DLI of the NL control averaged 9.9mol·m-2·d-1 during the growth period (ranging from 4 to 20mol·m-2·d-1). SL treatments and growing seasons significantly impacted biomass and nutrient bioaccumulation; some SL treatments had lower yields than the non-supplemented NL control. January growing season produced the lowest fresh mass (FM) and dry mass (DM) values compared to November, which had the highest. Mineral analyses revealed that both growing seasons and lighting types impacted macro and micronutrient accumulation. Additionally, the efficiency of each treatment in converting electrical energy into biomass varied greatly. EOD supplements using LED and HPS lighting systems both have merits for efficiently optimizing yield and nutrient accumulation in basil; however, biomass and nutrient tissue concentrations highly depend on seasonal variation in ambient sunlight in conjunction with a supplement's spectral quality, DLI, and application schedule.

Additive effects of light and branching on fruit size and chemical fruit quality of greenhouse tomatoes.

Greenhouse tomato growers face the challenge of balancing fruit size and chemical quality traits. This study focused on elucidating the interplay between plant branching and light management on these traits, while maintaining consistent shoot density. We evaluated one- and two-shoot plants under varying top light intensities using high-pressure sodium lamps and light-emitting diode (LED) inter-lighting. The reduced yield in the two-shoot plants was mainly due to smaller fruit size, but not due to source strength limitations, as evaluated through leaf weight ratio (LWR), chlorophyll index, specific leaf area (SLA), leaf dry matter percentage, and stem soluble carbohydrate accumulation. Enhanced lighting improved fruit weight and various fruit traits, such as dry matter content, total soluble carbohydrate content, and phenolic content, for both one- and two-shoot plant types. Despite lower mean fruit weight, two-shoot plants exhibited higher values for chemical fruit quality traits, indicating that the fruit growth of two-shoot plants is not limited by the available carbohydrates (source strength), but by the fruit sink strength. Diurnal analysis of fruit growth showed that two-shoot plants had reduced expansion during light transitions. This drop in fruit expansion was not related to changes in root pressure (measured as xylem sap exudation from decapitated plants), but might be related to diminished xylem area in the stem joint of the two-shoot plants. The concentration of several hormones, including cytokinins, was lower in two-shoot plants, suggesting a reduced fruit sink capacity. The predominant impact of branching to two-shoot plants on sink capacity suggests that the fruit growth is not limited by available carbohydrates (source strength). Alongside the observation that light supplementation and branching exert independent additive effects on fruit size and chemical traits, this illuminates the potential to independently regulate these aspects in greenhouse tomato production.

User behaviour in public squares after dark

This research concerns the influence of electric lighting on user behaviour in public squares and whether differences in people’s use of the square can be observed between daylight and darkness. Previous research on pedestrians suggests that lighting can support human needs for reassurance, accessibility, comfort and pleasure. While these findings are also likely to be applicable to the use of public squares, there is little empirical evidence to verify that. A field study was conducted to explore user behaviour in two differently illuminated public squares. Observations of the movements and stationary activities of people in the squares were recorded at both squares for the same times of day in the weeks before and after the daylight savings clock change, enabling a comparison of activity in daylight and after dark. 5296 observations were recorded and lighting conditions were captured with HDR-photography and aerial photos. Kirseberg square, with asymmetric luminaires and metal halide lamps, revealed a decrease in stationary activity after dark. Lindeborg square, with omnidirectional luminaires and high-pressure sodium lamps, revealed an increase in stationary activity. In conclusion, the patterns of user behaviour in the two public squares after dark seem to be differently influenced by electric lighting, pointing to a need for further understanding of users’ experience of the squares after dark.

What must be considered in winter strawberry production under LEDs in Iceland?

ABSTRACT 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.

Identifying the operational status of container terminals from high-resolution nighttime-light satellite image for global supply chain network optimization

Container terminals are cargo gateways in the global maritime supply chain network. Major container terminals generally operate throughout the year, but do not operate at night, when container vessels are not calling at ports, or when there is no need to handle containers. Terminal congestion can delay containers’ shipping schedules, which impacts the supply chain network. To optimize global logistics, it is therefore important to understand fully the daily operational status of container terminals. A vessels’ automatic identification system data are not sufficient to determine whether containers are being handled in container terminals at night. Remote sensing, especially nighttime-light (NTL) imagery, might solve this problem. Recently, high-resolution images for the CE-SAT-IIB satellite with a pixel resolution of 5.1 m became available to observe NTL. This study assessed the operational status of container terminals based on satellite image taken at night. Eight terminals in the Port of Tokyo, Japan, were selected for the study. A Sentinel-2A image recorded during the day on 7 April 2021, and a CE-SAT-IIB image recorded during the night on 6 April 2021, were obtained. The digital numbers (DNs) of each red-, green-, and blue-(RGB) band image were analyzed, revealing that the red, green, and blue bands, in that order, had higher DNs in the Sentinel-2A daytime image and the CE-SAT-IIB NTL image at all terminals. One of the eight terminals had a low DN in the CE-SAT-IIB RGB image because its lights were off at the time the image was taken. The operational status of the terminals could be verified from the CE-SAT-IIB image by setting the DN threshold to the green or red bands. We also found that the CE-SAT-IIB image could distinguish white-light-emitting diode (LED) lamps from high-pressure sodium lamps based on color differences in the DNs of the RGB bands. If high-resolution NTL sensors were placed onboard microsatellites, a high-frequency observation constellation network could be constructed using a combination of NTL data and daytime images. This study showed the benefits and usefulness of NTL images of ports; the results will contribute to the overall optimization of the global maritime supply chain network.