Non-uniform Light Distribution Research Articles

Effect of light intensity, spectrum, and uniformity on the ability of dairy cows to navigate through an obstacle course

The most suitable light intensity for cows during nighttime has not been thoroughly investigated. Recommendations on the night-time lighting regimen on dairy farms differ between countries and range from light throughout the night to darkness to allow the animals a rest from artificial light. Commercial actors recommend red light for night-time lighting in cattle barns to facilitate livestock supervision with minimum disturbance for the animals. However, little is known about how light intensity, spectrum, and uniformity affect the ability of cows to navigate their indoor environment. Thus, in a change-over study with 12 pregnant, nonlactating dairy cows, we observed how the cows walked through an obstacle course under different light treatments. Obstacles were positioned differently for every run, to present a novel challenge for each light environment. Fourteen different light treatments were tested, involving intensity ranging from <0.01 (darkness) to 4.49 µmol m-2 s-1, high or low uniformity, and white or red color. Light was characterized in terms of illuminance, photon flux density, spectral composition, and uniformity. Additionally, assessment of the environmental light field was used to describe each lighting condition from a bovine and human perspective. Data were analyzed in a generalized mixed model to assess whether lighting conditions affected cow walking speed or stride rate. Pair-wise post hoc comparisons showed that the cows walked at a slower speed in nonuniform red light compared with uniform white light or uniform red light. Interestingly, darkness did not alter walking speed or stride rate. The odds of different behaviors occurring were not affected by lighting conditions. In conclusion, darkness did not affect the ability of cows to navigate through the obstacle course, but medium-intensity, nonuniform red light affected their speed. Hence, cows do not necessarily need night-time lighting to navigate, even in a test arena with obstacles blocking their way, but nonuniform light distribution may have an effect on their movements.

Design and Optimization of Photovoltaic System in Full-Chain Ground-Based Validation System of Space Solar Power Station

In the face of the increasing depletion of non-renewable energy sources and increasingly serious environmental problems, the development of green and environmentally friendly renewable energy sources cannot be delayed. Because of the far-reaching development potential of solar energy, solar power has become an important research object for power development. The available solar energy in space is several times greater than that on Earth. Solar energy from space can be collected by a space solar power station (SSPS) and transmitted to the ground by wireless power transfer. In the full-chain ground-based validation system of SSPS-OMEGA, the spherical concentrator is used, and the light intensity distribution on the solar receiver is non-uniform. The non-uniform light intensity makes the output current of each photovoltaic (PV) cell on the solar receiver greatly different, and causes power losses, known as the mismatch problem. This paper proposes a simple, efficient and easy-to-implement method to optimize the structure of PV arrays to reduce the effect of non-uniform light on the output performance of each PV cell, which is beneficial to the topology of PV arrays and also effectively improves the layout rate. Then, a differential power processing (DPP) converter with a simple structure and easy control is designed to further deal with the power mismatch problem between series-connected PV modules. Finally, a simulation circuit model and a physical hardware model of the differential power processing PV system are built and used in the full-chain ground-based validation system of SSPS-OMEGA. The results demonstrate that the influence of non-uniform lighting on PV cells is effectively reduced, the output power of PV modules connected in series under non-uniform light distribution is substantially increased, and the photoelectric conversion efficiency is significantly improved.

Uniform Illumination Using Single-Surface Lens through Wavefront Engineering

Recent advancements in high power light-emitting diode (LED) technology have presented greenhouse industry with a more efficient and flexible alternative light source for horticulture. However, the light distribution on the plant remains a challenge that has notable implications on the plant growth. A non-uniform light distribution on the canopy with hot spots is well-known to adversely affect the yield. Here, we present a technique to engineer the light wavefront of a solid-state source using a single-surface optics, which yields a highly uniform light distribution across the plant. This technique achieves over 90% illuminance uniformity, preserved at various distances from the source, for a cone of light with an up to 120° angular range. This work aids the paradigm shift towards LEDs as a competitive light source in horticulture.

Digital PCR system development accelerator—A methodology to emulate dPCR results

The development of a digital polymerase chain reaction (dPCR) system typically begins with an idea for the system configuration and chip layout, followed by design, fabrication, and hardware testing. The image processing software can be developed and verified based on the test results. In this paper, we proposed a dPCR emulation methodology to train the developed image processing software before building the dPCR system hardware. We developed a script in a MATLAB environment to generate artificial dPCR images and emulate the dPCR results. First, we defined the number of parameters corresponding to the emulated results, such as the number of partitions with targets, background fluorescence distribution and intensity, image defects, image rotation angle, shift, non-uniform light distribution, and temperature sensitivity. We then implemented the defined parameters and generated an artificial dPCR chip image based on layout design or pattern recognition algorithm. Finally, we obtained a dataset from the artificial image for subsequent result analysis. The generated images could then be used to train the image processing algorithms based on the requirements. We verified the proposed method using various designs of dPCR chips from recently published papers, demonstrating the method's versatility. The proposed method also demonstrated the capability for separating the software and hardware development. Thus, our method allowed the image processing and hardware to be concurrently designed and tested simplifying and speeding up the dPCR system development.

Engineering waveguide surface by gradient etching for uniform light scattering in photocatalytic applications

In photoreactors, non-uniform light distribution leads to regions either with an overabundance of light or insufficient light irradiation. The integration of light-guiding elements such as waveguides into photocatalytic reactors has been an emerging approach to improve light delivery. However, traditional waveguides with constant surface properties experience an exponential decay in scattering light intensity under side irradiation. This reduces the light propagation length and hinders the scale-up potential. In this work, we derive the relationship between attenuation coefficients with etching time, determine the correlation between etching time and waveguide location for uniform scattering, and experimentally validate different light scattering profiles by engineering the surface roughness distribution of waveguides. We apply a dimensionless number, the coefficient of variation, to characterize the relative light distribution uniformity for gradient-etched, uniform-etched, and unmodified waveguides. Scattering light uniformity via gradient etching is more than 13 times higher than that for uniform-etching. In addition, the light distribution for gradient etching exhibits improved uniformity than other approaches, such as tip coating, physical carving, and engineered pillars. We then evaluate the effect of different light scattering profiles on photocatalytic activities in a photodegradation test for methylene blue, with non-etched, uniform-etched, and gradient-etched waveguides serving as internal light-guiding elements. Gradient-etched waveguides show ∼4 times improvement in photodegradation activity over uniform-etched designs and ∼8 times over non-etched configurations. This result underscores gradient etching for waveguides as a viable approach for precision light delivery to increase the light distribution uniformity, thus enhancing reaction rates for photocatalytic reactors.

Shape induced reflectance correction for non-destructive determination and visualization of soluble solids content in winter jujubes using hyperspectral imaging in two different spectral ranges

Abstract Soluble solids content (SSC) is an important quality attribute in determining fruit maturity and grading after harvest. This study explored the potential of hyperspectral imaging (HSI) coupled with multivariate analysis in visible and near-infrared (Vis-NIR, 380−1030 nm) and near-infrared (NIR, 874−1734 nm) regions for measuring SSC in winter jujube fruit. The effectiveness of applying area normalization to reduce the influence of non-uniform light distribution on the spherical surface of intact fruit was explored. Then linear and non-linear regression models were developed and compared in two spectral ranges. The performance obtained by the least squares-support vector machine (LS-SVM) models based on successive projection algorithm (SPA) was satisfactory. The determination coefficient of prediction (Rp2) and residual predictive deviation (RPD) were 0.873 and 2.81 for the NIR range, and 0.894 and 3.07 for the Vis-NIR range, respectively. The SPA-LSSVM models were applied on the pixel-wise and object-wise spectra of region of interest before and after area normalization for comparison of visualization performance of corresponding prediction maps for SSC. Area normalization could effectively correct the non-uniform reflectance on a spherical object. The overall results indicated that HSI could be used to non-destructively predict and visualize SSC in winter jujubes.

Highly efficient Mn-doped CsPb(Cl/Br)3 quantum dots for white light-emitting diodes

White light-emitting diodes (WLEDs) based on all-inorganic perovskite CsPbX3 (X = Cl, Br, I) quantum dots (QDs) have attracted much attention and rely on mixing several colors of perovskites. However, this inevitably leads to a non-uniform light distribution and serious light loss. Here, a novel strategy was demonstrated to obtain white emission by combining the orange and blue emission from CsPb/Mn(Cl/Br)3 QDs. Notably, highly efficient white emission with a photoluminescence quantum yield of 94% was achieved by an anion exchange surface engineering (AESE) strategy. After AESE treatment the surface traps can be eliminated, resulting in improved exciton and Mn2+ emission. A prototype WLED device was fabricated and exhibited excellent optical stability, demonstrating great potential for perovskite QDs in the field of optoelectronics.

Large depth focus-tunable photoacoustic tomography based on clinical ultrasound array transducer

Multi-element photoacoustic tomography systems have either a non-movable focus or a non-uniform light field distribution over the region of interest, significantly limiting the depth-of-field and resolution of images. In this study, focus-tunable photoacoustic tomography (FT-PAT) based on a clinical ultrasound array transducer with uniform laser excitation was developed to achieve high-resolution imaging in deep tissue. An adjustable line-focusing structure was used to condense the laser beam, and the excited photoacoustic signal was processed via a synthetic-aperture focusing technique. Carbon rods at different depths were used to evaluate the focus-tunable ability in a tissue phantom. In vivo focus-tunable imaging performance was demonstrated by an experiment involving imaging of carbon nanoparticle-labeled living nude mouse covered by chicken breast. The signal-to-noise ratio of targets at different depths was changed by focus adjustment, which demonstrates that the FT-PAT system has potential clinical applications in deep tumor imaging and subsequent diagnoses.

Performance of SiPMs and pre-amplifier for the wide field of view Cherenkov telescope array of LHAASO

The Wide Field of View Cherenkov Telescope Array (WFCTA), a main component of the Large High Altitude Air Shower Observatory (LHAASO), is designed for cosmic rays spectrum measurement from 30 TeV to several EeV. Silicon photomultipliers (SiPMs) have been adopted for the telescope cameras as they do not suffer any aging even with strong light exposure and thus they can be operated with moonlight. The physics of WFCTA requires a dynamic range of SiPMs to be within 10 p.e. (photoelectrons) to 32, 000 p.e. at any energy range. And the dynamic range of SiPMs is proportional to the total number of APDs and depends on the distribution of light hitting on the active area. This light distribution is affected by the use of light concentrator and also by the use of spherical mirrors of the telescope. The effect of these two factors on the Cherenkov light distribution has to be taken into account to evaluate the dynamic range and in this work they have been simulated with a ray-tracing software. The non-uniform light distribution caused by the light concentrator and the spherical mirror will be below 2% for 32, 000 p.e. at the condition if the SiPM has 360, 000 cells. The characteristics of SiPMs from three different producers – Hamamatsu, FBK, and SensL – are measured in laboratory, and the dynamic range of them has also been measured using a uniform light flux. The results of dynamic range correspond with the calculation by the function which describes the relationship between the number of fired APDs and the total number of APDs in the SiPM. The performance of the SiPMs and PMTs under long time duration light pulses up to 3 μs are compared, in order to investigate the stability of the gain of the SiPMs for the fluorescence mode.

Optical properties and resonant cavity modes in axial InGaN/GaN nanotube microcavities

Microcavities based on group-III nitride material offer a notable platform for the investigation of light-matter interactions as well as the development of devices such as high efficiency light emitting diodes (LEDs) and low-threshold nanolasers. Disk or tube geometries in particular are attractive for low-threshold lasing applications due to their ability to support high finesse whispering gallery modes (WGMs) and small modal volumes. In this article we present the fabrication of homogenous and dense arrays of axial InGaN/GaN nanotubes via a combination of displacement Talbot lithography (DTL) for patterning and inductively coupled plasma top-down dry-etching. Optical characterization highlights the homogeneous emission from nanotube structures. Power-dependent continuous excitation reveals a non-uniform light distribution within a single nanotube, with vertical confinement between the bottom and top facets, and radial confinement within the active region. Finite-difference time-domain simulations, taking into account the particular shape of the outer diameter, indicate that the cavity mode of a single nanotube has a mixed WGM-vertical Fabry-Perot mode (FPM) nature. Additional simulations demonstrate that the improvement of the shape symmetry and dimensions primarily influence the Q-factor of the WGMs whereas the position of the active region impacts the coupling efficiency with one or a family of vertical FPMs. These results show that regular arrays of axial InGaN/GaN nanotubes can be achieved via a low-cost, fast and large-scale process based on DTL and top-down etching. These techniques open a new perspective for cost effective fabrication of nano-LED and nano-laser structures along with bio-chemical sensing applications.

Adjoint-driven Russian roulette and splitting in light transport simulation

While Russian roulette (RR) and splitting are considered fundamental importance sampling techniques in neutron transport simulations, they have so far received relatively little attention in light transport. In computer graphics, RR and splitting are most often based solely on local reflectance properties. However, this strategy can be far from optimal in common scenes with non-uniform light distribution as it does not accurately predict the actual path contribution. In our approach, like in neutron transport, we estimate the expected contribution of a path as the product of the path weight and a pre-computed estimate of the adjoint transport solution. We use this estimate to generate so-called weight window which keeps the path contribution roughly constant through RR and splitting. As a result, paths in unimportant regions tend to be terminated early while in the more important regions they are spawned by splitting. This results in substantial variance reduction in both path tracing and photon tracing-based simulations. Furthermore, unlike the standard computer graphics RR, our approach does not interfere with importance-driven sampling of scattering directions, which results in superior convergence when such a technique is combined with our approach. We provide a justification of this behavior by relating our approach to the zero-variance random walk theory.

Optofluidic membrane microreactor for photocatalytic reduction of CO2

Photocatalytic reduction of CO2 is a promising technology to capture CO2 and convert it into solar fuels simultaneously. However, current photoreactors usually face the problems of low specific surface area, non-uniform light distribution and poor photon transfer. To address these issues, a novel optofluidic membrane microreactor with high surface-area-to-volume ratio, enhanced photon and mass transport and uniform light distribution was proposed in this work by combining optofluidics with the membrane reactor technology for the photocatalytic reduction of CO2 with liquid water. A TiO2/carbon paper composite membrane was prepared as the photocatalytic membrane via coating TiO2 onto the carbon paper followed by hydrophobic treatment by poly-tetrafluoroethylene (PTFE) for the separation of the gas/liquid phases. The performance of the proposed optofluidic membrane microreactor was evaluated by measuring the methanol yield. The effects of the liquid water flow rate, light intensity and catalyst loading on the methanol yield were also studied. It was shown that a maximum methanol yield of 111.0 μmole/g-cat·h was achieved at a flow rate of 25 μL/min and under the light intensity of 8 mW/cm2, which is among the top in comparison to the reported data. Results obtained fully demonstrate the feasibility and superiority of the proposed optofluidic membrane microreactor for the photocatalytic reduction of CO2.

Effects of Nonuniform Incident Illumination on the Thermal Performance of a Concentrating Triple Junction Solar Cell

A numerical heat transfer model was developed to investigate the temperature of a triple junction solar cell and the thermal characteristics of the airflow in a channel behind the solar cell assembly using nonuniform incident illumination. The effects of nonuniformity parameters, emissivity of the two channel walls, and Reynolds number were studied. The maximum solar cell temperature sharply increased in the presence of nonuniform light profiles, causing a drastic reduction in overall efficiency. This resulted in two possible solutions for solar cells to operate in optimum efficiency level: (i) adding new receiver plate with higher surface area or (ii) using forced cooling techniques to reduce the solar cell temperature. Thus, surface radiation exchanges inside the duct and Re significantly reduced the maximum solar cell temperature, but a conventional plain channel cooling system was inefficient for cooling the solar cell at medium concentrations when the system was subjected to a nonuniform light distribution. Nonuniformity of the incident light and surface radiation in the duct had negligible effects on the collected thermal energy.

Deformable mirrors with thermo-mechanical actuators for extreme ultraviolet lithography: Design, realization and validation

Abstract In lithographic illumination systems, a nonuniform light distribution causes local deformations on the mirrors used. Active mirrors are a solution to correct these deformations by reshaping the surface. This paper presents the deformation of a mirror with thermo-mechanical actuators placed perpendicular to the surface. Two deformable mirrors are modeled, realized and validated: one with seven and one with 19 actuators. By placing the actuators on a thin back plate, the force loop is localized and therefore a lower actuator coupling is achieved. The thermo-mechanical actuators are free from mechanical hysteresis and therefore have a high position resolution with high reproducibility. Extensive Finite Element Analysis is done, to maximize actuator stroke and minimize input power. The mirrors are tested and validated with interferometer surface measurements and thermocouple temperature measurements. A mirror deflection of 0.68 nm/K is realized and no hysteresis is observed. Thermal step responses are fitted and both heating and cooling characteristic time constants are 2.5 s. The thermal actuator coupling from an energized actuator to its direct neighbor is 6.0%. The total actuator coupling is approximated around 10%, based on the good agreement between simulated and measured inter-actuator stroke.

Concentrating PV/T Hybrid System for Simultaneous Electricity and Usable Heat Generation: A Review

Photovoltaic (PV) power generation is one of the attractive choices for efficient utilization of solar energy. Considering that the efficiency and cost of PV cells cannot be significantly improved in near future, a relatively cheap concentrator to replace part of the expensive solar cells could be used. The photovoltaic thermal hybrid system (PV/T), combining active cooling with thermal electricity and providing both electricity and usable heat, can enhance the total efficiency of the system with reduced cell area. The effect of nonuniform light distribution and the heat dissipation on the performance of concentrating PV/T was discussed. Total utilization of solar light by spectral beam splitting technology was also introduced. In the last part, we proposed an integrated compound parabolic collector (CPC) plate with low precision solar tracking, ensuring effective collection of solar light with a significantly lowered cost. With the combination of beam splitting of solar spectrum, use of film solar cell, and active liquid cooling, efficient and full spectrum conversion of solar light to electricity and heat, in a low cost way, might be realized. The paper may offer a general guide to those who are interested in the development of low cost concentrating PV/T hybrid system.

Evanescent photosynthesis: exciting cyanobacteria in a surface-confined light field

The conversion of solar energy to chemical energy useful for maintaining cellular function in photosynthetic algae and cyanobacteria relies critically on light delivery to the microorganisms. Conventional direct irradiation of a bulk suspension leads to non-uniform light distribution within a strongly absorbing culture, and related inefficiencies. The study of small colonies of cells in controlled microenvironments would benefit from control over wavelength, intensity, and location of light energy on the scale of the microorganism. Here we demonstrate that the evanescent light field, confined near the surface of a waveguide, can be used to direct light into cyanobacteria and successfully drive photosynthesis. The method is enabled by the synergy between the penetration depth of the evanescent field and the size of the photosynthetic bacterium, both on the order of micrometres. Wild type Synechococcus elongatus (ATCC 33912) cells are exposed to evanescent light generated through total internal reflection of red (λ = 633 nm) light on a prism surface. Growth onset is consistently observed at intensity levels of 79 ± 10 W m(-2), as measured 1 μm from the surface, and 60 ± 8 W m(-2) as measured by a 5 μm depthwise average. These threshold values agree well with control experiments and literature values based on direct irradiation with daylight. In contrast, negligible growth is observed with evanescent light penetration depths less than the minor dimension of the rod-like bacterium (achieved at larger light incident angles). Collectively these results indicate that evanescent light waves can be used to tailor and direct light into cyanobacteria, driving photosynthesis.

Microelectrode systems for the study of photochemical processes in solution

Three systems for photoelectrochemical measurements on the microscale have been implemented and compared: (i) an arrangement in which a fibre illuminates a disc-shaped ultramicroelectrode (UME) face-on; (ii) face-on illumination of a ring UME; and (iii) illumination through a fibre-coupled ring UME assembly. These set-ups have been used to study the classic system in which photoexcited tris(2,2′-bipyridine) ruthenium (II), Ru ( bpy ) 3 2 + , reduces methyl viologen dication, MV 2+, to the radical cation, MV +. Detection of MV + at the UME allows the kinetics to be determined and mass-transport at the various configurations to be assessed. It is shown that face-on illumination of either disc or ring-shaped UMEs can be treated in a straight forward way with simplifications such as a uniform light intensity distribution. On the other hand, while the fibre-coupled ring arrangement is potentially easier and simpler to deploy, it does not appear as amenable to such straightforward treatments. Deviations between experiment and theory in the latter case are attributed to complications such as natural convection and non-uniform light distribution, to which this format appears to be more sensitive.

Hydrogen Production by Photoreactive Nanoporous Latex Coatings of Nongrowing Rhodopseudomonas palustris CGA009

Nonuniform light distribution is a fundamental limitation to biological hydrogen production by phototrophic bacteria. Numerous light distribution designs and culture conditions have been developed to reduce self-shading and nonuniform reactivity within bioreactors. In this study, highly concentrated (2.0 x 108 CFU/muL formulation) nongrowing Rhodopseudomonas palustris CGA009 were immobilized in thin, nanoporous, latex coatings. The coatings were used to study hydrogen production in an argon atmosphere as a function of coating composition, thickness, and light intensity. These coatings can be generated aerobically or anaerobically and are more reactive than an equivalent number of suspended or settled cells. Rhodopseudomonas palustris latex coatings remained active after hydrated storage for greater than 3 months in the dark and over 1 year when stored at -80 degrees C. The initial hydrogen production rate of the microphotobioreactors containing 6.25 cm2, 58.4 mum thick Rps. palustris latex coatings illuminated by 34.1 PAR mumol photons m-2 s-1 was 6.3 mmol H2 m-2 h-1 and had a final yield of 0.55 mol H2 m-2 in 120 h. A dispersible latex blend has been developed for direct comparison of the specific activity of settled, suspended, and immobilized Rps. palustris.

Determination of optimal view angles for quantitative facial image analysis

In quantitative evaluation of facial skin chromophore content using color imaging, several factors such as view angle and facial curvature affect the accuracy of measured values. To determine the influence of view angle and facial curvature on the accuracy of quantitative image analysis, we acquire cross-polarized diffuse reflectance color images of a white-patched mannequin head model and human subjects while varying the angular position of the head with respect to the image acquisition system. With the mannequin head model, the coefficient of variance (CV) is determined to specify an optimal view angle resulting in a relatively uniform light distribution on the region of interest (ROI). Our results indicate that view angle and facial curvature influence the accuracy of the recorded color information and quantitative image analysis. Moreover, there exists an optimal view angle that minimizes the artifacts in color determination resulting from facial curvature. In a specific ROI, the CV is less in smaller regions than in larger regions, and in relatively flat regions. In clinical application, our results suggest that view angle affects the quantitative assessment of port wine stain (PWS) skin erythema, emphasizing the importance of using the optimal view angle to minimize artifacts caused by nonuniform light distribution on the ROI. From these results, we propose that optimal view angles can be identified using the mannequin head model to image specific regions of interest on the face of human subjects.

Optical properties of Dictyostelium discoideum pseudoplasmodia responsible for phototactic orientation

Pseudoplasmodia of Dictyostelium discoideum detect the light direction measuring an internal, nonuniform distribution of light. The organism acts as a cylindrical lens which focuses parallel lateral light onto the distal flank of the organism. The focal band can be demonstrated optically and can be calculated mathematically based on geometrical optics. The refractive index of homogenized pseudoplasmodia is 1.369 ± 0.001 (SEM), while the calculated refractive index, based on measurements of the focal bands and using an iterative technique, is 1.371 ± 0.001 (SEM). The nonuniform internal light distribution produced by the lens effect can be reversed by incorporating an internal absorbing screen pigment, neutral red, into the pseudoplasmodia or by focusing the laterally impinging parallel light onto the proximal flank, both of which cause a negative phototactic orientation.