Low Light Intensity Research Articles

Escape of etiolated hypocotyls of cotton (Gossypium hirsutum) from the unilateral high intensity blue light after being pulled out from the soil.

Plant stems grow towards the incident light in response to unilateral blue light to optimize photosynthesis. However, our findings reveal that unilateral high-intensity blue light (HBL) triggers backlit lodging in etiolated cotton (Gossypium hirsutum ) hypocotyls when they are pulled approximately 1.5cm from the soil. Phenotypic analysis indicated that stomata on the lit side were open, while those on the shaded side were closed under unilateral HBL. To investigate the relationship between stomatal movement and backlit lodging, we applied abscisic acid (ABA), hydrogen peroxide (H2 O2 ), and lanthanum chloride (LaCl3 ) to the lit side, and cytokinins (6-BA) and ascorbic acid (ASA) to the shaded side. Results showed that all these treatments inhibited the backlit lodging phenomenon, specifically, ABA, H2 O2 , and LaCl3 reduced stomatal opening on the lit side, while 6-BA and ASA enhanced stomatal opening on the shade side. These results demonstrate that HBL-induced asymmetrical stomatal opening on the lit and shade side of hypocotyl supports the backlit lodging phenomenon. Notably, maize (Zea mays ), which lack stomata in the hypocotyl did not exhibit HBL-induced backlit lodging, whereas soybean (Glycine max ), which has stomata in its etiolated hypocotyl, displayed a similar phenotype to that of cotton. Additionally, while both red light and low-intensity blue light (LBL) can induce stomatal opening, they do not trigger the backlit lodging phenomenon. These findings suggest that backlit lodging is a unique HBL-dependent response, but the mechanism need further investigation.

CLFNet: a multi-modal data fusion network for traffic sign extraction

Abstract When using image data for signage extraction, poor visibility conditions such as insufficient light, rainy days, and low light intensity are encountered, leading to low accuracy and poor boundary segmentation in vision-based detection methods. To address this problem, we propose a cross-modal latent feature fusion network for signage detection, which obtains rich boundary information by combining images with light detection and ranging depth images, thus compensating for the pseudo-boundary phenomenon that may occur when using a single RGB image segmentation. First, HRNet is utilized as the backbone network to extract the boundary information of the point cloud depth map and RGB image by introducing the boundary extraction module; Second, the sensitivity to the boundary is enhanced by applying the feature aggregation module to deeply fuse the extracted boundary information with the image features; Finally, boundary Intersection over Union (IOU) is introduced as an evaluation index. The results show that the method performs more superiorly compared to the mainstream RGBD network, with an improvement of 5.5% and 6.1% in IOU and boundary IOU, and an accuracy of 98.3% and 96.2%, respectively, relative to the baseline network.

Insight into gain and transient response characteristics of AlGaN/GaN hetero-junction based UV photodetectors: Case study on the role of incident light intensity

Gain and response speed are two key performance parameters for high sensitivity photodetectors (PDs). However, the effect of incident light intensity on gain and transient response properties of AlGaN/GaN hetero-junction based PDs are still not fully understood. Here, we design and fabricate an AlGaN/GaN hetero-junction based ultraviolet (UV) PD with interdigitated electrodes formed by a conductive two-dimensional electron gas (2DEG) channel, which exhibits a low dark current of 2.92 × 10−11 A and a high responsivity of 3060 A/W at 10 V bias. The high-gain AlGaN/GaN 2DEG PD has a similar working mechanism to those of traditional phototransistors, but its device architecture is evidently simplified. By investigating the variation of gain and transient response characteristics of the 2DEG PD as a function of incident UV light intensity, it has been concluded that the gain of the PD in a low-light intensity region is dominated by hole accumulation-induced electron escape from the 2DEG, while in a high-light intensity region, the gain is dominated by photoconductivity effect and limited by carrier recombination. This study provides guidance for future practical applications of AlGaN/GaN-based PDs in complex UV illumination environments.

Improving effectiveness of environmental enrichment: the role of light intensity in rock bream (Oplegnathus fasciatus) rearing

Environmental enrichment is a potential approach to enhance the fitness and survival of hatchery fish stocked for conservation purposes. Its effectiveness presumably depends not only on ecologically relevant features of physical enrichment but also on light condition applied. Despite the importance, few studies have reported on the role of light in enriched rearing. This study sought to optimize the enriched rearing of juvenile rock bream (Oplegnathus fasciatus) particularly regarding their physiological and behavioral performance by regulating light intensity. Juveniles were reared in either standard tanks (no enrichment) or enriched tanks with polyethylene ropes simulating drifting algae at three different light intensities (400, 800 or 1600 lux) for 32 days. Our findings revealed that cortisol levels of the fish increased with light intensity even in the presence of the physical structure. No significant effect of light intensity was detected on growth. Compared to standard fish, fish reared with enrichment showed higher levels of caudal fin damage and cortisol at all the light intensities, suggesting increased chronic stress; in addition, the fish displayed higher shelter-seeking behavior. These results highlight the importance of maintaining low light intensities to minimize chronic stress in the fish. Moreover, adjustments to the enriched rearing condition are recommended to mitigate adverse effects on physiological aspects before incorporated into practical implementation in stock enhancement programs.

Optimizing Light Intensity and Salinity for Sustainable Kale (Brassica oleracea) Production and Potential Application in Marine Aquaponics

With rising populations and increasing food consumption, the demand for food is placing significant strain on freshwater resources. Exploring crops that can thrive under saline conditions is crucial to ensuring food security. Although brackish and seawater is abundant, it is generally unsuitable for irrigation. However, some plants exhibit tolerance to moderate levels of salinity. This study investigated the effects of varying light intensities (150 and 250 photosynthetic photon flux densities) and salinity levels (<1.5, 5, 10, and 17 parts per thousand, equivalent to <26, 86, 171, and 291 millimolars) on the growth and nutrient composition of Russian kale (Brassica oleracea) grown in indoor hydroponics. The experiment was conducted over five months, from September 2023 to January 2024. The results revealed that a light intensity of 250 PPFD and salinity levels of <1.5–5 ppt (<26–86 mM) were optimal for maximizing the biomass yield of the kale, whereas a significant reduction in the yield was observed at salinity levels exceeding 10 ppt (171 mM). In contrast, the dry matter percentage was significantly higher at 17 ppt (291 mM). The macronutrient contents, particularly the total Kjeldahl nitrogen (TKN), total phosphorus (TP), and magnesium (Mg), were consistent across both light intensities (150–250 PPFDs) and at salinity levels between <1.5 and 10 ppt (<26–171 mM) but were reduced at 17 ppt (291 mM). The micronutrient concentrations, such as those of copper (Cu), iron (Fe), and zinc (Zn), were higher at the lower light intensity (150 PPFD) across the salinity levels. These findings suggest that optimizing the light conditions is essential for enhancing the nutritional value of kale in saline environments. These outcomes are particularly vital for improving agricultural productivity and resilience in salt-affected regions, thereby supporting broader food security and sustainability goals.

Low light recognition of traffic police gestures based on lightweight extraction of skeleton features

With the increasing demand for information interaction between intelligent vehicles and traffic managers, understanding traffic police commands has become an essential element in achieving human–computer interaction. The aim of this study is to investigate the low light traffic police gesture recognition based on lightweight extraction of skeleton features. A two-stage recognition framework for eight gesture commands is proposed. The first stage utilizes convolutional neural networks to acquire the human skeleton under low light. The second stage utilizes a recurrent neural network to construct a lightweight feature extraction model for gesture recognition. HRnet acquires spatial features of the action, high-resolution and multi-scale fusion circumvents the effect of low-light intensity. Self-attention (SA) mechanism and MobileNet lightweight feature extraction have addressed the time-consuming issue in the feature extraction phase. The improved GRU network is used to extract time domain features, the fusion of spatio-temporal features improves the recognition accuracy. For training and validation, a gesture dataset (TPGD) containing 3391 gesture instances is constructed. The proposed method obtains 94.75% accuracy in the TPGD test set, demonstrating its effectiveness. This study holds significant importance for enhancing the level of intelligence in traffic management, promoting the development of intelligent transportation systems, and ensuring road traffic safety.

Hydrogel impeller formation via vacuum degassing photopolymerization for micromixers

For effective mixing within microfluidic devices through the application of obstacle-based structures, a straightforward approach involves in-situ fabrication, such as the free-radical photopolymerization of hydrogel structures. However, oxygen inhibition presents a challenge for polydimethylsiloxane (PDMS)-based microfluidic chips. In this paper, we present a solution to the problem of hydrogel-structure formation hindered by oxygen inhibition at low light intensities and the photoinitiator concentration achieved using vacuum degassing. Furthermore, a kinetic model for photopolymerization under vacuum conditions was established and converted into an equation of light intensity and exposure time while keeping the other parameters constant. The exposure time range was successfully predicted by comparing the experimental data and analyzing scenarios. This method was used to fabricate an impeller for a passive micromixer. The impeller rotation was then analyzed. The results demonstrated that with an increased flow rate exceeding 6 mL/min, the mixing efficiency is significantly higher owing to the rotation of the impeller. The mixing efficiency was quantitatively assessed through experiments involving the mixing of three dyes, showing a three-fold increase compared to the chip without the impeller. Our research provides valuable insights into the fabrication of hydrogel structures in PDMS-based microfluidic chips under vacuum conditions.

Noninvasive Ultra Low Intensity Light Photodynamic Treatment of Glioblastoma with Drug Augmentation: LoGlo PDT Regimen

Noninvasive Ultra Low Intensity Light Photodynamic Treatment of Glioblastoma with Drug Augmentation: LoGlo PDT Regimen

Shallow corals acclimate to mesophotic depths while maintaining their heat tolerance against ongoing climate change

Global warming poses a significant threat to coral reefs. It has been assumed that mesophotic coral ecosystems (MCEs, 30 to 150 m depths) may serve as refugia from ocean warming. This study examined the acclimation capacity and thermal tolerance of two shallow coral species, Porites cylindrica and Turbinaria reniformis, transplanted to mesophotic depths (40 m) for 12 months. Fragments from 5 and 40 m were exposed to control (28 °C), moderate (30 °C), and high (32 °C) temperatures over 14 days. MCE-acclimated fragments showed higher thermal thresholds and survival rates, delayed onset of bleaching, and less decline in photosynthesis efficiency (Fv/Fm) compared to shallow fragments. Both species maintained high thermal tolerance despite prolonged exposure to cooler temperatures of mesophotic depth. These findings suggest that low light intensity in MCEs can act as a modulator of bleaching, supporting the potential of these ecosystems as refugia for shallow corals in a rapidly changing world.

Minimizing Voltage Deficit in Perovskite Indoor Photovoltaics by Interfacial Engineering.

Metal halide perovskites with bandgap of ≈1.8eV are competitive candidates for indoor photovoltaic (IPV) devices, owing to their superior photovoltaic properties and ideal absorption spectra matched to most indoor light sources. However, these perovskite IPVs suffer from severe trap induced non-radiative recombination, resulting in large open-circuit voltage (VOC) losses, particularly under low light intensity. Herein, an effective approach is developed to minimizing trap density by modifying the buried interface of perovskite layer with bifunctional molecular 2-(4-Fluorophenyl)ethylamine Hydrobromide (F-PEABr). The benzene ring of F-PEABr molecules can firmly anchor at the hole transporting layer by π-π stacking interaction, and the other ends can passivate the defects on the buried interface of perovskite layer. Based on that, the F-PEABr modified perovskite IPVs achieved power conversion efficiency (PCE) of 42.3% with a remarkable VOC of 1.13V under 1000 lux illumination from a 4000K LED lamp. Finally, perovskite IPV mini-modules with area of 10.40cm2 are demonstrated with a PCE of 35.2%. This interface modification strategy paves the way for crafting high-performance perovskite IPVs, holding great potential for self-powered internet of things applications.

Light-dependent switching between two flagellar beating states selects versatile phototaxis strategies in microswimmers

Microorganisms have evolved sophisticated sensor-actuator circuits to perform taxis in response to various environmental stimuli. How any given circuit can select between different taxis responses in noisy vs. saturated stimuli conditions is unclear. Here, we investigate how Euglena gracilis can select between positive vs. negative phototaxis under low vs. high light intensities, respectively. We propose three general selection mechanisms for phototactic microswimmers, and biophysical modeling demonstrates their effectiveness. Perturbation and high-speed imaging experiments show that of these three mechanisms, the "photoresponse inversion mechanism" is implemented in E. gracilis: a fast, light-intensity-dependent switching between two flagellar beat states responsible for swimming and turning causes positive vs. negative phototaxis at low vs. high light intensity via run-and-tumble vs. helical klinotaxis strategies, respectively. This coordinated beat-switching mechanism then also accounts for a larger set of previously reported E. gracilis behaviors; furthermore, it suggests key design principles for other natural as well as synthetic microswimmers.

Large photoresistance and photoinduced magnetoresistance in La0.67Ca0.33MnO3 thin film on silicon substrate

Abstract The effects of light illumination and magnetic field on the electrical transport properties of La0.67Ca0.33MnO3 thin film on a silicon substrate have been studied in detail. Large value of colossal magnetoresistance has been observed under an applied magnetic field in the whole temperature range below 150 K which is related to the presence of both antiferromagnetic and ferromagnetic phase in the sample. A significant amount of resistance drop is caused by light illumination even at extremely low light intensities, ∼−22% with light of 0.3 μW cm−2 intensity and ∼−42% with 6.2 μW cm−2 intensity at 600 nm wavelength. There has been a notable rise in the photoinduced magnetoresistance value, specifically, a significant decrease in resistance occurs in simultaneous presence of magnetic field and light. For 1 T applied magnetic field, MR% rises from −33% in dark to −58% under light illumination at 150 K i.e. ΔMR% is 25%. As the strength of the magnetic field increases, ΔMR% decreases, suggesting that the magnetoresistive photoinduced phenomenon is more pronounced in the presence of mix phases in the sample. This combined enhanced magnetoresistive photoinduced phenomenon is explained by the interaction of photogenerated charge carriers in the sample and applied magnetic field.

Self-sensitization-induced protonation sites for weak-light-driven hydrogen evolution in coordination polymers

The exploration on weak-light-driven catalysis is an important approach to reduce the dependence of photocatalysts on strong light and improve the efficiency of solar spectrum utilization. However, the reported photocatalysts typically necessitate high light intensity (e.g., exceeding 100 mW cm−2) for catalytic reactions, which cannot be achieved with natural solar light. Herein, a self-sensitization-induced strategy was employed to generate in-situ proton sites, enabling photocatalytic hydrogen evolution reaction (HER) even under low light intensity (10 mW cm−2). An indolocarbazole ligand (H2ICDB) was utilized to construct a paddle-wheel dicopper coordination polymer (CuICDB-DMF). By substituting the axially coordinated DMF with methanol or water, CuICDB-MeOH and CuICDB-H2O were obtained. Under weak-light irradiation (10 mW cm−2), CuICDB-H2O exhibited the highest photocatalytic HER rate of 838.4 μmol g−1 h−1 when compared to the other two counterparts. Remarkably, the substitution of axially coordinated H2O promotes charge separation and transfer efficiency through optimizing ligand-to-cluster charge transfer (LCCT) process. Moreover, density functional theory (DFT) calculations reveal that coordinated H2O substitution decreases the Gibbs free energy difference of the potential determining step (H2O* → OH* + H*) in CuICDB-H2O.

Exposure to constant artificial light alters honey bee sleep rhythms and disrupts sleep

Artificial light at night (ALAN) changes animal behavior in multiple invertebrates and vertebrates and can result in decreased fitness. However, ALAN effects have not been studied in European honey bees (Apis mellifera), an important pollinator in which foragers show strong circadian rhythmicity. Colonies can be exposed to ALAN in swarm clusters, when bees cluster outside the nest on hot days and evenings, and, in limited cases, when they build nests in the open. We captured and maintained foragers in incubated cages and subjected them to constant light (LL), constant dark (DD), or 12 h light:12 h dark (LD) cycle, and observed them with infrared cameras. After 79 h, there was a significant interaction of treatment and time because LL bees slept less. In detail, the bees maintained a regular sleep pattern for three days but LL bees showed a shift on the fourth day. LL bees had the largest sleep differences from LD controls, with trends of lengthened periods and increased phase misalignment from both LD and DD bees. LL bees also experienced significantly more disturbances from their nestmates and preferred to sleep in the lower portion of the cages, which had significantly lower light intensity. These findings suggest that ALAN can disrupt the sleep of honey bee foragers, which has implications for their behavior and overall colony health.

Light Energy Use Efficiency in Photosystem II of Tomato Is Related to Leaf Age and Light Intensity

The fundamental key to increase photosynthetic efficiency of crop plants lies in optimizing the light energy use efficiency. In our study, we used tomato to evaluate the allocation of absorbed light energy in young and mature leaves, and to estimate if the extent of photoinhibition and photoprotection can be affected by the leaf age. A reduced efficiency of the oxygen-evolving complex, in young leaves compared to mature ones, resulted in a donor-side photoinhibition, as judged from the significantly lower Fv/Fm ratio, in young leaves. The detected increased 1O2 production in young leaves was probably due to a donor-side photoinhibition. The effective quantum yield of photosystem II (PSII) photochemistry (ΦPSII), at low light intensity (LLI, 426 μmol photons m−2 s−1), was significantly lower in young compared to mature leaves. Moreover, the non-significant increase in non-photochemical energy loss in PSII (ΦNPQ) could not counteract the decreased ΦPSII, and as a result the non-regulated energy loss in PSII (ΦNO) increased in young leaves, compared to mature ones. The significantly lower ΦPSII in young leaves can be attributed to the increased reactive oxygen species (ROS) creation that diminished the efficiency of the open PSII reaction centers (Fv’/Fm’), but without having any impact on the fraction of the open reaction centers. The reduced excess excitation energy, in mature leaves compared to young ones, at LLI, also revealed an enhanced PSII efficiency of mature leaves. However, there was almost no difference in the light energy use efficiency between young and mature leaves at the high light intensity (HLI, 1000 μmol photons m−2 s−1). The ability of mature tomato leaves to constrain photoinhibition is possible related to an enhanced photosynthetic function and a better growth rate. We concluded that the light energy use efficiency in tomato leaves is influenced by both the leaf age and the light intensity. Furthermore, the degrees of photoinhibition and photoprotection are related to the leaf developmental stage.

Giant Controllable Near-Infrared Nonlinear Amplification in Metal Nanoparticles-Graphene Nanodisks-Quantum Dots Plasmonic Hybrid Systems with Low Light Intensity

Giant Controllable Near-Infrared Nonlinear Amplification in Metal Nanoparticles-Graphene Nanodisks-Quantum Dots Plasmonic Hybrid Systems with Low Light Intensity

An Improved UNet-Based Path Recognition Method in Low-Light Environments

The fruit industry is a significant economic sector in China, with modern orchards gradually transitioning to trellis orchards. For mechanized orchard operations, automatic vehicle navigation is essential. However, in trellis orchards, the shading from trees results in low average light intensity and large variations in lighting, posing challenges for path navigation. To address this, a path navigation algorithm for trellis orchards is proposed based on the UNet-CBAM model. The network structures of UNet, FCN, and SegNet are compared to identify and select the optimal structure for further improvement. Among the three attention mechanisms of channel attention, spatial attention, and combined attention, the most effective mechanism is identified. The optimal attention mechanism is incorporated into the optimized network to enhance the model’s ability to detect path edges and improve detection performance. To validate the effectiveness and generalizability of the model, a total of 400 images were collected under varying lighting intensities. The experimental results show that this method achieves an accuracy of 97.63%, a recall of 93.94%, and an Intersection over Union (IoU) of 92.19%. These results significantly enhance path recognition accuracy in trellis orchards, particularly under low light under conditions. Compared to the FCN and SegNet algorithms, this method provides higher detection accuracy and offers a new theoretical foundation and research approach for path recognition in low-light environments.

A self-powered interface circuit for piezoelectric and photovoltaic energy extracting

This paper presents a high-efficiency multi-source energy harvesting system consisting of a piezoelectric rectifier, a photovoltaic maximum power point tracking circuit and a fast self-startup circuit for powering wireless sensor nodes. Synchronous electric charge extraction techniques (SECE) are utilized to extract the piezoelectric energy when the deflection of piezoelectric energy harvester beam reaches its peak. Compared with other circuits, the proposed SECE technique can achieve piezoelectric and photovoltaic extraction simultaneously with a concise flyback topology structure. A novel maximum power point tracking method is adopted to enhance the robustness of operation against changing operating condition and improve the photovoltaic extraction efficiency. To remove the need for a battery, a simple and efficient self-startup circuit is introduced. The energy harvesting circuit is fabricated in 180 nm CMOS process. Measurement results show a fast self-startup at a relatively low light intensity of 120 lux is realized. The energy harvesting circuit is capable of outputting 189 μW power at 3.3 V piezoelectric open circuit voltage and 0.6 V photovoltaic input voltage.

Improvement in photosynthesis under different light intensities is highly linked to domestication stages in cotton.

Domestication has dramatically increased crop size and biomass, reflecting the enhanced accumulation of photosynthates. However, we still lack solid empirical data on the impacts of domestication on photosynthetic rates at different light intensities and on leaf anatomy, and of the relationships of photosynthesis with aboveground biomass. In this study, we measured the photosynthetic rate at three photosynthetic photon flux densities of 2000 (high), 1000 (moderate) and 400 μmol m-2 sec-1 (low light intensity), dark respiration, relative chlorophyll content (SPAD), leaf morphology, and aboveground biomass in 40 wild, 91 semiwild, and 42 domesticated cotton genotypes. The study was replicated for two years (growing years 2018 and 2019). During the first domestication stage (transition from wild to semiwild genotypes), domestication led to higher photosynthetic rates measured under high light intensity, higher SPAD, larger leaf area (LA), and lower leaf mass per unit area (LMA), contributing to greater aboveground biomass accumulation in both study years. During the second domestication stage (transition from semiwild to domesticated genotypes), domestication significantly enhanced photosynthesis under low light intensity and reduced LMA, which were associated with increased aboveground biomass in both study years. In conclusion, photosynthesis improvement at different light intensities has been a gradual domestication phase specific process with the rate of photosynthesis enhanced under high light during the first domestication stage, and under low light during the second domestication stage. We argue that these differences reflect a higher proportion of LA photosynthesizing under low light due to enhanced canopy expansion at the second domestication stage.

A combined stereolithography and a pressureless sintering method to prepare SiC ceramics

The use of submicron silicon carbide powder as a raw material is crucial for preparing high-performance silicon carbide ceramics. However, its strong absorption of ultraviolet light makes stereolithography of submicron silicon carbide powder challenging. In this study, submicron SiC particles, photosensitive resin, and photoinitiator were used as raw materials to prepare SiC ceramics via stereolithography combined with a pressureless sintering method. The effects of ultraviolet wavelength, type, and content of photoinitiator on the curing properties of submicron SiC ceramic slurry were investigated. The results showed that the curing thickness of the SiC ceramic slurry significantly increased with the increasing ultraviolet wavelength. Compared to photoinitiators TPO and 396, photoinitiator 819 exhibited a better curing effect. Additionally, increasing the photoinitiator content facilitated the generation of more free radicals in the SiC ceramic slurry at low light intensity, thereby improving its ultraviolet absorption characteristics. When the dosage of photoinitiator 819 was 8.8 %, the SiC slurry achieved the best curing performance, with a single-layer curing thickness of 50 μm and a sintering density of 95 % for SiC ceramics.