Real Light Sources Research Articles

Estimation of the sensitivity of optical measurements using a holographic interferometer

Various interferometers used for high-precision spectroscopic measurements are considered, and the choice of a holographic interferometer based on the spatial-spectral method of holographic interferometry is justified, with the help of which the movements of the phase center of a coherent light flux in a wide dynamic range are measured in real time and measurement information is recorded digitally. On the basis of mathematical relations proposed by the authors in previous publications and based on the results of experimental studies, the sensitivity of a holographic interferometer to spatial displacements of phase centers (focus points) of light streams – point light sources forming a holographic interferogram is numerically estimated. The dependence of the level of the normalized intensity of the luminous flux in the central region of the holographic interferogram on the movement of the actual point light source along the normal to the plane of the Fourier hologram is established. Based on the results of mathematical modeling, it is shown that the sensitivity of the holographic interferometer to the movements of a real point light source along the normal to the plane of the Fourier hologram depends on the parameters of the optical scheme of the holographic interferometer when exposing the hologram and during measurements. At the same time, the sensitivity of the holographic interferometer to the indicated displacements of a real point light source can only be evaluated experimentally. It is proposed to increase the sensitivity of the holographic interferometer by using a thin collecting lens in its optical scheme. For the first time, a mathematical relation was obtained and investigated for the gain coefficient of the light flux phase with a spherical wavefront, which makes it possible to numerically estimate the increase in sensitivity of a holographic interferometer implementing the spatial-spectral method of holographic interferometry with known parameters of a thin collecting lens in an optical scheme. It is shown that the sensitivity of a holographic interferometer to the movements of an imaginary point light source along the normal to the plane of the Fourier hologram is 2.86 times greater than its sensitivity to the same movements of a real point light source. It is established that the sensitivity of a holographic interferometer with a volumetric Fourier hologram and a thin collecting lens in its design can be increased by at least an order of magnitude compared to the sensitivity of known optical interferometers. The results of assessing the sensitivity of a holographic interferometer implementing the spatial-spectral method of holographic interferometry to the movements of point sources of real and imaginary light fluxes, as well as the obtained ratio for the gain of the light flux phase gain by a thin collecting lens will be useful for high-precision measurements of linear and angular displacements of objects, as well as for the construction of photonic device designs. Based on the results of the study, an experimental sample of an acousto-electric converter was developed and manufactured on the basis of a holographic interferometer, which has high sensitivity in wide dynamic and frequency ranges and is intended for use in acoustic location of unmanned aerial vehicles.

Logarithmic total variation regularization via preconditioned conjugate gradient method for sparse reconstruction of bioluminescence tomography

Background and objectiveBioluminescence Tomography (BLT) is a powerful optical molecular imaging technique that enables the noninvasive investigation of dynamic biological phenomena. It aims to reconstruct the three-dimensional spatial distribution of bioluminescent sources from optical measurements collected on the surface of the imaged object. However, BLT reconstruction is a challenging ill-posed problem due to the scattering effect of light and the limitations in detecting surface photons, which makes it difficult for existing methods to achieve satisfactory reconstruction results. In this study, we propose a novel method for sparse reconstruction of BLT based on a preconditioned conjugate gradient with logarithmic total variation regularization (PCG-logTV). MethodThis PCG-logTV method incorporates the sparsity of overlapping groups and enhances the sparse structure of these groups using logarithmic functions, which can preserve edge features and achieve more stable reconstruction results in BLT. To accelerate the convergence of the algorithm solution, we use the preconditioned conjugate gradient iteration method on the objective function and obtain the reconstruction results. We demonstrate the performance of our proposed method through numerical simulations and in vivo experiment. Results and conclusionsThe results show that the PCG-logTV method obtains the most accurate reconstruction results, and the minimum position error (LE) is 0.254mm, which is 26%, 31% and 34% of the FISTA (0.961), IVTCG (0.81) and L1-TV (0.739) methods, and the root mean square error (RMSE) and relative intensity error (RIE) are the smallest, indicating that it is closest to the real light source. In addition, compared with the other three methods, the PCG-logTV method also has the highest DICE similarity coefficient, which is 0.928, which means that this method can effectively reconstruct the three-dimensional spatial distribution of bioluminescent light sources, has higher resolution and robustness, and is beneficial to the preclinical and clinical studies of BLT.

Optical ray-tracing simulation method for the investigation of radiance non-uniformity of an integrating sphere

The paper deals with possibilities and limits of optical simulations of extended uniform light sources. Optical simulations of ideal and real light sources are performed using optical ray-tracing software which is capable to simulate non-imaging systems such as Lambertian disc and integrating spheres. The simulation methodology is validated by comparing the developed simulation model with a real experiment previously performed in optical laboratory. The comparison is made on the radiance uniformity measurement and simulation results of a general purpose integrating sphere rather than on less convenient and more frequent irradiance uniformity measurements. The aim is to develop a reliable simulation method for the investigation of radiance non-uniformity of any real extended uniform light source.

Calibration of brightness of virtual reality light sources based on user perception in the real environment

Accurately conveying brightness information and improving the reducibility of the perceived visual scene are important aspects of the efforts to promote the application of virtual reality (VR) in light environment research. In this study, brightness perception threshold (BPT) experiments with controlled, repeatable conditions were conducted in equivalent real and VR environments using the minimum change method. The experiments were conducted with the luminance, shape, size, and position of the light-emitting surfaces as variables, using 20 distinct surface forms. After 28 participants finished the assessment, the experimental data were analyzed using SPSS. The analysis shows that the initial luminance, shape, and size all have significant influence on the BPT in both real and VR environments, and the influence rules are consistent. The effect of the positions of the light-emitting surfaces on the BPT varies depending on the shape. Based on the BPT data, the Number of Perceptions (NOP) was proposed as an intermediate variable, and 15 brightness calibration curves for VR and real environment light sources were established. This study uses the consistency of visual brightness to establish the correspondence between the VR presentations’ brightness and the physical illumination of real scenes, which has implications for improving the accuracy of VR applications to light environment research and design.

Improved Method for Evaluating and Specifying the Chromaticity of Light Sources

ABSTRACT This article describes a method for calculating and specifying light source chromaticity using the International Commission on Illumination (CIE) 2015 10° color matching functions (CMFs), which, according to analysis of existing psychophysical experiment data, can reduce visual mismatch compared to specifications based on the traditional CIE 1931 2° CMFs in architectural lighting applications. Specifically, this work evaluates, documents, and recommends for adoption by lighting standards organizations a supporting system of measures to be used with the CIE 2015 10° CMFs: a new uniform chromaticity scale (UCS) diagram with coordinates (s, t), a measure of correlated color temperature (CCTst), and a measure of distance from the Planckian locus (Dst). It also presents options for updating nominal classification quadrangles. A complete method of this nature has not yet been standardized, which may be contributing to the slow uptake of the CIE 2015 CMFs. The proposed tools are analogous to u, v, CCT, Duv, and the American National Standards Institute (ANSI) C78.377 chromaticity specifications that are all currently defined in the CIE 1960 UCS diagram using the CIE 1931 2° CMFs. While conceptually equivalent, the differences between the current standard method and the proposed st system are important for reducing unintended visual mismatch in the chromaticity of light. The implications of changing chromaticity specification methods are identified by a comparison over a diverse set of real light source spectral power distributions.

Highly efficient solar-light-driven photocatalytic degradation of pollutants in petroleum refinery wastewater on hierarchically-structured copper sulfide (CuS) hollow nanocatalysts

The high solar-light-driven activity of HS-CuS-HNCs was ascribed to its narrow band gap, strong visible-light absorption and high quantum efficiency characteristics, and especial the synergistic effect between HS-CuS-HNCs and H 2 O 2 . • HS-CuS-HNCs were prepared in high yield by a simple method at room temperature. • HS-CuS-HNCs showed high solar-light-driven activity. • The synergistic effect led to produce more reactive oxygen species (ROS). • The capabilities of ROS to reduce COD followed the sequence: •O 2 − > 1 O 2 > •OH. • A novel nanophotocatalyst was provided for utilizing solar energy efficiently. Hierarchically-structured CuS hollow nanocatalysts (HS-CuS-HNCs) were prepared in high yield (>95%) by a simple chemical solution deposition method at room temperature, and then used to photocatalytically degrade pollutants in petroleum refinery wastewater (PRW) under solar light radiation. Compared to bulk-size CuS catalyst, HS-CuS-HNCs with narrower band gap (E g = 0.96 eV) exhibited strong visible-light absorption, highly enhanced quantum efficiency and large specific area (101.5 m 2 g −1 ) characteristics. HS-CuS-HNCs showed significantly enhanced activity for the degradation of pollutants under both artificial and real solar light source (about 66% of COD in PRW was removed in 3 h degradation under conditions of 1.0 g/L catalyst and 7.6 pH). The activity of HS-CuS-HNCs was drastically enhanced further in the presence of hydrogen peroxide (H 2 O 2 ) (98% of COD in PRW was removed in 2 h under conditions of 1.0 g/L catalyst, 3.0 g/L H 2 O 2 and 7.6 pH), which was attributed to the synergistic effect between HS-CuS-HNCs and H 2 O 2 , leading to the enhanced quantum efficiency and production of more reactive oxygen species (ROS). Radical-quenching experiments revealed that the contributions of ROS to COD reduction in PRW followed the sequence: superoxide anion (•O 2 − ) > singlet oxygen ( 1 O 2 ) > hydroxyl radical (•OH). Important factors such as catalyst dose, H 2 O 2 dose and initial pH had influences on the degradation efficiency. This work provided a hierarchically-structured non-TiO 2 -based nanophotocatalyst with high performance for efficiently utilizing solar energy to oxidatively degrade pollutants in PRW fast and deeply.

Development of a High-Flux Solar Simulator for Experimental Testing of High-Temperature Applications

In the last few years, several studies have been carried out on concentrating solar thermal and thermochemical applications. These studies can be further enhanced by means of high-flux solar simulators (HFSS), since they allow the development of experimental tests under controlled irradiance conditions, regardless of sunshine. In this work, a new high-flux solar simulator, capable of reaching levels of irradiance higher than 100 W/cm2 (1000 suns), has been designed, built and characterized. This simulator is composed of 8 ellipsoidal specular reflectors, arranged face-down on a horizontal plane, in order to irradiate from the upper side any system requiring the simulation of concentrated solar radiation; differently from the HFSSs described in the scientific literature, this configuration allows the avoidance of any distortion of fluid-dynamic or convective phenomena within the system under investigation. As a first step, a numerical analysis of the HFSS has been carried out, simulating each real light source (Xe-arc), having a length of 6.5 mm, as a line of 5 sub-sources. Therefore, the HFSS has been built and characterized, measuring a maximum irradiance of 120 W/cm2 and a maximum temperature of 1007 °C; these values will be enough to develop experimental tests on lab-scale thermal and thermochemical solar applications.

Восстановление положения источников освещения сцены в системах смешанной реальности с использованием сверточных нейронных сетей и трассировки теневых лучей

The paper examines the causes of visual discomfort in mixed reality systems and algorithmic solutions that eliminate one of the main causes of discomfort, namely, the mismatch between the lighting conditions of objects in the real and virtual worlds. To eliminate this cause of discomfort, the algorithm is proposed, which consists in constructing groups of shadow rays from points on the boundaries of shadows to points on the boundaries of objects. Part of the rays corresponding to the real lighting conditions form caustics in area of the real light source, which makes it possible to determine the source of illumination of virtual objects for their correct embedding into the mixed reality system. Convolutional neural networks and computer vision algorithms were used to classify shadows in the image. Examples of reconstructing the coordinates of a light source from RGBD data are presented.

Exploring the Determinants of Color Perception Using #Thedress and Its Variants: The Role of Spatio-Chromatic Context, Chromatic Illumination, and Material-Light Interaction.

The colors that people see depend not only on the surface properties of objects but also on how these properties interact with light as well as on how light reflected from objects interacts with an individual’s visual system. Because individual visual systems vary, the same visual stimulus may elicit different perceptions from different individuals. #thedress phenomenon drove home this point: different individuals viewed the same image and reported it to be widely different colors: blue and black versus white and gold. This phenomenon inspired a collection of demonstrations presented at the Vision Sciences Society 2015 Meeting which showed how spatial and temporal manipulations of light spectra affect people’s perceptions of material colors and illustrated the variability in individual color perception. The demonstrations also explored the effects of temporal alterations in metameric lights, including Maxwell’s Spot, an entoptic phenomenon. Crucially, the demonstrations established that #thedress phenomenon occurs not only for images of the dress but also for the real dress under real light sources of different spectral composition and spatial configurations.

Detection of real-time augmented reality scene light sources and construction of photorealis tic rendering framework

In this paper, the main network of multi-channel light sources is improved, so that multi-channel pictures can be fused for joint training. Secondly, for high-resolution detection pictures, the huge memory consumption leads to a reduction in batches and then affects the model distribution. Group regularization is adopted. We can still train the model normally in small batches; then, combined with the method of the regional candidate network, the final detection accuracy and the accuracy of the candidate frame regression are improved. Finally, through in-depth analysis, based on image lighting technology and physical-based rendering theory, the requirements for lighting effects and performance limitations, combined with a variety of image enhancement technologies, such as gamma correction, HDR, and these technologies used in Java. Real-time lighting algorithms that currently run efficiently on mainstream PCs. The algorithm can be well integrated into the existing rasterization rendering pipeline, while into account better lighting effects and higher operating efficiency. Finally, the lighting effects achieved by the algorithm are tested and compared through experiments. This algorithm not only achieves a very good light and shadow effect when rendering virtual objects with a real scene as the background but also can meet the realistic rendering of picture frames in more complex scenes. Rate requirements. The experimental results show that the virtual light source automatically generated by this algorithm can approximate the lighting of the real scene, and the virtual object and the real object can produce approximately consistent lighting effects in an augmented reality environment with one or more real light sources.

Beam characterization by phase retrieval solving the transport-of-intensity-equation.

A new method for the characterization of coherent laser beams is proposed. It is based on the non-iterative solution of the transport-of-intensity-equation. The phase to recover is decomposed into paraxial properties of laser beams and a set of lateral shifted radial basis functions, which allows for the derivation of a direct solution of the phase by a least-squares fit without the need of an initial guess. The method is tested with synthetic data to deduce an accuracy metric. Additionally, two real laser beams are characterized. Including the real light source in terms of the reconstructed field allows for a more holistic simulation of optical systems.

Optical coherence tomography modeling incorporating scattering, absorption, and multiple reflections.

A direct scattering optical coherence tomography forward model was developed to simulate A-scans for both idealized and real light sources on an arbitrary given sample structure. Previous models neglected absorption, scattering, and multiple reflections at interfacial layers, and so two extended models were developed to investigate the impact of these processes. The first model uses the Beer-Lambert law to incorporate both absorption and scattering optical processes, and the second model uses a recursive form to model multiple reflections. These models were tested on a structure representative of a multilayered skin sample. The results show that the absorption and scattering processes have significant impact on the height of the peaks in the simulated A-scans. Conversely, the incorporation of multiple reflections has very little impact on the height of these peaks. Neither of the above processes has any impact on the locations of the A-scan peaks, which are associated with the sample interfaces between layers.

Compact freeform illumination system design for pattern generation with extended light sources.

One of the major problems in freeform illumination design in a geometrical optics approximation is picture generation with extended light sources. In contrast to the freeform design with zero-étendue sources, the extension of the light source leads to the typical blurring effect and a contrast reduction of the required irradiance. This effect can be minimized by increasing the distance between the freeform surface and the light source, which according to étendue conservation, results in an impractically large projection optic. To tackle this problem, we propose a design concept consisting of the combination of a pattern-generating double freeform surface for collimated beam shaping, which is calculated for a zero-étendue light source, and an imaging projection system with a telecentric object space. The design concept works independently of the shape of the emission area of the light source and does not require a representation of the extended light source by several individual wavefronts. By interpreting the pattern blurring effect as a composition of a shift contribution and a distortion contribution, we show that both can be minimized simultaneously by an appropriate placement of the object plane of the imaging optics and by making the distance between both freeform surfaces as small as possible. This allows the calculation of compact, energy-efficient freeform illumination systems for picture generation with real extended light sources. We demonstrate the significant blurring reduction by designing a simple illumination system consisting of a collimation optic, a (zero-étendue) double freeform lens for collimated beam shaping, and a projection lens for the generation of the target distribution "Elaine" with an extended Lambertian emitter of 3 mm×3 mm extension and ±42 deg maximum opening angle. For a working distance to the projection system of 500 mm and a target area of 300 mm×300 mm, a relative blurring extension of 2% is estimated, compared to 23% for a single freeform projector with the same energy throughput and similar lateral extension. The influence of the doublefreeform thickness on the blurring reduction is demonstrated, and a summary of the design procedure for the developed design concept is given.

Real-time adaptable and coherent rendering for outdoor augmented reality

This paper describes the development and evaluation of a color estimation method that is able to create more natural lighting conditions for outdoor-purposed augmented reality (AR) technology. In outdoor AR systems, the real outdoor light source (i.e., the sun) illuminates real objects, while a virtual light source illuminates the augmented virtual objects. These two light sources result in color differentials, with the real object and virtual object being visualized as a mixture of the colors induced by the two light sources. As such, there is a visible difference in color between the real object and the virtual object. Consequently, this visible color difference will vitiate the sense of immersion felt by the AR user. Thus, to overcome this problem, we have defined each RGB color channel value by analyzing the color generated by the outdoor light source and applied the defined values to the virtual light source to reduce the visibility of the color differential between the two light sources, thereby reducing the visualized incompatibility between the virtual object and the real background. In addition, using virtual objects to express weather events, in combination with the color estimation method, we were able to demonstrate that the proposed method can adequately adapt to and manage the weather changes that affect outdoor AR. The proposed method has the potential to improve the visual coincidence between the real outdoor background and virtual objects.

Simulating the photon stream of a real thermal light source.

We present a computer algorithm capable of simulating the photon stream and the corresponding temporal photon statistics of thermal light sources. The algorithm implements realistic experimental conditions, incorporating the relevant parameters of the source as well as of the detection process. The code is verified by comparing the temporal photon autocorrelation function computed from the simulations to the one measured with a real thermal light source. In view of the renewed interest for intensity interferometry in astronomy and the life sciences, such simulations become increasingly relevant.

Method of Determination of RMS Exposure of Ex-tended Source Image by Microphotometry

Background. Among the parameters and functions to assess the quality of images formed by optical systems RMS spot diagrams parameter is used. This option is usually defined by beam ray-tracing going through optical system. There is a fundamental ability to regenerate RMS by microphotometry of image of real point light sources. However, the RMS of the image is distorted due to finite size source. The problem is that the separation of RMS components values, which are caused by the parameters of the light source and the optical system aberrations.Objective. The recovery of RMS aberration component based on the results of microphotometry of image of extended source of radiation generated with optical system to be tested.Methods. The mathematical tools polar calculations were used, axial and centrifugal RMS from distribution function of illumination in the image of the extended light source, close to the spot. The calculations of mentioned RMS types are conducted by the radii formulas for moments of inertia that are known in theoretical mechanics. Analogue mass they contain is spatial density of luminous flux in the optical image source. In calculating of RMS the source length is included using Huygens- Steiner theorem.Results. New mathematical observations for calculation of RMS including illumination distribution in the image of light sources are obtained. It was established that RMS of each type is Pythagorean sum of components, one of which is specified by the parameters of the source, and the other by the aberrations of the optical system. According to the results of the regenerated RMS from microphotometry of the image of source and the data on the source parameters aberrational component can be determined in each RMS type.Conclusion. The study confirms the possibility of determining the aberration RMS of the optical system according to the results of microphotometry of image of extended light source. The method allows creating new photoelectrical hardware for measuring distances to objects, and to create new types of ophthalmic devices.

SOFT SHADOWS USING SP-LINE APPROXIMATION

Realistic soft shadows are an important factor to enhance the realism of Augmented Reality systems. Without shadows, virtual objects would look floating over the scene resulting unrealistic rendering of AR environment. Little attention has been directed towards balanced trade-off between shadow quality and computational cost. In this study, a new approach is proposed; Quadratic Sp-line Interpolation (QSI) to soften the outline of the shadow. QSI estimates the border of hard shadow samples. In more details, a reflective hemisphere is used to capture real light then to create an environment map. Implementation of the Median Cut algorithm is performed to locate the direction of real light sources on the environment map. Subsequently, the original hard shadows are retrieved and a sample of multilayer hard shadows is produced. The proposed technique is tested by using three samples of multilayer hard shadows with a varied number of light sources that are generated from the Median Cut algorithm. The experimental results show that the proposed technique has successfully produced realistic soft shadows with low computational costs.

Position-Dependent Importance Sampling of Light Field Luminaires

The possibility to use real world light sources (aka luminaires) for synthesizing images greatly contributes to their physical realism. Among existing models, the ones based on light fields are attractive due to their ability to represent faithfully the near-field and due to their possibility of being directly acquired. In this paper, we introduce a dynamic sampling strategy for complex light field luminaires with the corresponding unbiased estimator. The sampling strategy is adapted, for each 3D scene position and each frame, by restricting the sampling domain dynamically and by balancing the number of samples between the different components of the representation. This is achieved efficiently by simple position-dependent affine transformations and restrictions of Cumulative Distributive Functions that ensure that every generated sample conveys energy and contributes to the final result. Therefore, our approach only requires a low number of samples to achieve almost converged results. We demonstrate the efficiency of our approach on modern hardware by introducing a GPU-based implementation. Combined with a fast shadow algorithm, our solution exhibits interactive frame rates for direct lighting for large measured luminaires.

Best lighting for visual appreciation of artistic paintings—experiments with real paintings and real illumination

In a previous study based on monitor simulations of artistic paintings, it was found that the average correlated color temperature (CCT) of daylight preferred by a large set of observers to illuminate paintings was around 5100 K. The goal of the present study was to test if this result holds in real viewing conditions, i.e., with real paintings and real light sources. The same 11 paintings were tested in real conditions illuminated by a spectrally tunable light source and with accurate monitor simulations. To ensure uniform illumination across the paintings, only a central part of the paintings was visible to the observers. It was found that the average CCT preferred for real and monitor viewing conditions were very similar, 5500 and 5700 K, respectively. The somewhat larger CCT obtained with monitor viewing in relation to the former study was only observed in some paintings and was attributed to the smaller viewing area. These results confirm that CCT for best appreciation of paintings is higher than normally used in museums, and the viewing conditions, real or simulated, have only a minor effect.

Measuring, simulating and optimizing current LED phosphor systems to enhance the visual quality of lighting

Lighting engineering aspects of light emitting diodes (LEDs) with down converting phosphors (phosphor converted LEDs or PC-LEDs) were investigated by building sample PC-LEDs, measuring their spectral emission physically and simulating them with a software. This article describes the influence of the phosphors’ chemical, physical and technological properties on some well-established and widely used measures of visual lighting quality including luminous efficacy and the color rendering index. The dependence of these measures on YAG and LuAG phosphor particle size and activator concentration in the PC-LEDs is dealt with. Light sources of superior lighting quality can be obtained by mixing several phosphors. Hence, the mixture of a green and red phosphor system was also studied for a set of real PC-LED light sources and their simulations. Two green and two red phosphors are considered in this study. To predict and optimize the lighting quality of PC-LEDs with a reasonable accuracy, a usable input shall be provided for the simulation software assuming the understanding of the emission mechanisms. To validate our simulation results, the PC-LEDs’ measured spectral emission characteristics were compared with their simulated counterparts. The measurement and simulation of spectral power distributions contribute to the understanding of new phosphor mixtures. The present simulation method turned out to be usable to optimize the target parameters of the PC-LED (luminous efficacy, white tone quality and color quality of the illuminated colored objects).