Light Source Model Research Articles

紧凑型LED配光设计中光源模型可靠性研究

紧凑型LED配光设计中光源模型可靠性研究

Relationship between Peak Wavelength and Dominant Wavelength of Light Sources Based on Vector-Based Dominant Wavelength Calculation Method

ABSTRACTCurve fitting and lookup table methods based on vector relationships are proposed to compute dominant wavelength (DW), which is used to characterize hue. A curve-fitting method using a DW–angle relationship is simple but not very accurate, with an error of about 1 to 2 nm. A lookup table method is proposed for higher precision. The methods have been applied to study the relationships between peak wavelength and DW for Gaussian models of light sources’ spectra. For Gaussian models, DW varies as full-width at half maximum (FWHM) increases from 5 to 500 nm, and the trends differ at different peak wavelengths. For purity, as peak wavelength changes from 430 to 530 nm, the purity’s decreasing rate monotonically increases with FWHM, whereas as peak wavelength changes from 530 to 680 nm, the purity’s decreasing rate monotonically decreases with FWHM. Peak wavelength contours and FWHM contours are drawn for determination of DW and purity. The results should be useful for estimating DW (hue) of the Gaussian models of light sources’ spectra, which can guide the spectral design of light sources.

A New Welding Process Simulation Using a Hybrid Particle and Grid Method with Explicit MPS

During welding, the weld pool has a fluid flow with thermal conduction and a free surface. The dropped metal also supplies a free surface. These complex phenomena are difficult to simulate using the grid method. On the other hand, particle methods, such as the smoothed-particle hydrodynamics (SPH) method or the moving particle semi-implicit (MPS) method, can evaluate the fluid flow and the thermal conduction with a free surface more easily than grid methods. In the present study, for high-speed and effective simulation of the welding process, including the weld pool, a hybrid particle and grid method with explicit MPS is performed. In this hybrid method, particles can be used in the weld pool and the area located near the weld pool, whereas grid elements are used in the other areas. Furthermore, in order to consider interface effects, a light source model for the welding process simulation is developed. As a result, numerical simulation of the heat conduction in the weld joint, including the fluid flow in the weld pool with a free surface, is performed. During welding, the weld pool has a fluid flow with thermal conduction and a free surface. The dropped metal also supplies a free surface. These complex phenomena are difficult to simulate using the grid method. However, particle methods such as smoothed-particle hydrodynamics (SPH) [1] or the moving particle semi-implicit (MPS) method [2], which represents the fluid flow as moving particles, can more easily evaluate the fluid flow and thermal conduction with a free surface than grid methods. However, particle methods generally need to simulate equal particle sizes. This means that the calculation cost using particle methods is larger than that using grid methods. Therefore, an analysis using the particle method is effective for the weld pool, but not for the full-size weld joint. In the present study, first, for high-speed, effective simulation of the welding process, including the weld pool, explicit MPS [3, 4] is performed. Second, a hybrid particle and grid method [5] is used for welding process simulation. In the hybrid method, particles can be used in the weld pool and the area located near the weld pool, whereas grid elements are used in the other areas. Furthermore, in order to add the interface effects, which are caused by the arc pressure and the heat input, a light source model for the welding process simulation is developed. The model can consider the radiated effects of the heat source. As a result, numerical simulation of the heat conduction in the weld joint, including the fluid flow in the weld pool, is performed.

Optical detection sensitivity of area light source in optical read-out IR imaging

In the theoretical analysis of the optical readout IR imaging, the incoherent area light source with a certain size is typically simplified into an ideal point light source, which leads to analytical errors. In this paper an area light source model is established, and using the Fraunhofer diffraction theory the influence of the optical detection sensitivity on area light source is studied. The dependence of the optical detection sensitivity on light source radius and reflector length of the focal plane array is found. And optimized design criteria for the size of light source and the length of the reflector are proposed. According to theoretical analysis, the experimental verification is carried out, and the results are consistent with theoretical analyses.

A virtual reality design for learning the basic concepts of synchrotron light source

This study investigated the virtual reality technology to develop a virtual synchrotron light source model and its learning contents for applications in the curriculum of science and life technology in elementary and junior high schools. The objective is to increase the interest and effectiveness of young students in learning this advanced technology and its applications. The factors of student age, gender and correlation with the performance in previous science courses were also investigated to see if they would affect the learning effectiveness. A teaching experiment was conducted and the results showed that the model was effective in helping students understand the basic concepts of synchrotron light source and its applications. Student age and gender had no obvious influence on the learning achievement, but a significant positive correlation was found between students' performance in their previous science courses and the learning achievement. Also, the questionnaire results revealed that most students were very interested in using the virtual light source model and its learning contents.

An improved image blind identification based on inconsistency in light source direction

In this study, an improved image blind identification algorithm based on inconsistency in light source direction was proposed. And a new method defined as "neighborhood method" was presented, which was used to calculate surface normal matrix of image in the blind identification algorithm. For an image, there is an error function between its actual light intensity and calculated light intensity, and for different light source models, there are different constraint functions of light. Light source direction which makes both error function and constraint function get the minimum is the one we want to seek. On this basis, according to the error function and the corresponding constraint function, search means and the Hestenes---Powell multiplier method were used in the improved algorithm to calculate the light source direction for local and infinite light source images, respectively. Further, the authenticity of image can be determined by the inconsistency in light source direction of different areas in the image. Experimental results showed that the light source direction of different areas in an image could be calculated accurately, and then the image tampering can be detected effectively by the improved algorithm. Moreover, the performance of the improved algorithm of the proposed blind identification is superior to that of the existing one in terms of detection rate and time complexity.

Layouts and Cells in Integral Photography and Point Light Source Model

The similarity between two groups of displaying methods is demonstrated in two ways, analytically and experimentally. A variety of layouts of the integral photography and display devices based on the point light source model is classified and analyzed in terms of projections and common/separate image planes. In particularly, the transformation matrix is found. Simulation experiments based on the image processing were performed. The layouts, analytical formulas, and experimental results show the similarity of both groups for several layouts.

SIMULATION STUDY OF IMPACT OF ENERGY SAVING EFFECT AND INDOOR ENVIRONMENT BY DAYLIGHTING

The light source models All Sky Models reproducing daylight and solar radiation comprehensively are installed to ray-tracer RADIANCE calculating inter-reflections with reflection distribution accurately. Furthermore, a program converting the irradiance distribution to heat boundary conditions of CFD analysis is developed. In this paper, the developed programs predicted the daylight illuminance, radiation load and irradiance distribution with inter-reflection of shades, and energy saving effects of artificial lighting and air conditioning was evaluated under the same analysis method. Then, applying CFD analysis the difference was found in the temperature distributions under the heat boundary conditions of irradiance distribution between the calculation by the developed programs and the calculation by the easy method. As a result, the availability of the programs is indicated.

A unified framework for scene illuminant estimation

Most existing illuminant estimation algorithms work with assumptions of specific source types (e.g. directional light source or point light source). The assumptions bring up two main limitations which significantly restrict their applicabilities: first, the prior knowledge about source types is needed; second, it can not handle complex scenes where multiple source types co-exist. In this paper, we develop a general light source model which is designed to model arbitrary light sources. With the general source model, we are able to estimate multiple illuminants of different types within a single unified framework. We use a plastic sphere to probe both diffuse and specular reflections of a scene. With specular reflections, we estimate geometric parameters of the illuminants by a novel ray tracing and matching algorithm. The diffuse reflections are used to estimate photometric parameters of the illuminants. We also notice that common source types are degenerate cases of the general source model under certain conditions. Therefore, we can approximate light sources with common source types by checking the conditions. The approximations serve as type determinations of light sources, which makes our framework extremely useful for lighting related algorithms which need prior knowledge about light sources. Experiment results on a variety of real images demonstrate the efficiency and accuracy of our algorithm.

Far-field pattern simulation of flip-chip bonded power light-emitting diodes by a Monte Carlo photon-tracing method

The far-field pattern of light-emitting diodes (LEDs) is an important issue in practical applications. We used a Monte Carlo photon-tracing method for the package design of flip-chip bonded power LEDs. As a first-order approximation, we propose using a plane light source model to calculate the far-field pattern of encapsulated LEDs. The far-field pattern is also studied by use of a more detailed model, which takes the structure of all epitaxial layers of a flip-chip bonded power LED into consideration. By comparing the simulation results with the experimental data, we have concluded that the plane light source model is much less time-consuming and offers fairly good precision for package design.

Detecting changes of buildings using stereo matching from aerial images taken at different positions and times

AbstractGIS base maps are updated by using parallax to compare two aerial images taken at different times to interpret structural changes. Since an aerial image generally photographs a wide range, this interpretation work requires a great deal of time. Therefore, in this paper, the authors propose a method of automatically extracting structural changes with high precision to reduce the load of this interpretation work. Not only do the times differ at which the aerial images used for comparison were taken, but the shooting positions also frequently differ. This causes differences in shadow shapes and differences in structure viewing methods, and when aerial images are compared during automatic interpretation, it will cause the detection precision of structural changes to decrease. To deal with this problem, the authors eliminated the effects of differences in structure viewing methods by applying stereo matching and letting noncorresponding regions be structural change candidates. In addition, to correctly detect structural changes from those candidates, the authors used the outdoor light source model, which had been proposed by previous authors, to eliminate the effects of differences in shadow shapes. The results that were obtained by the proposed method showed that the detection precision of structural changes was approximately four times that of the conventional method. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 87(6): 55–65, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjc.20084

Accurate light source acquisition and rendering

Realistic image synthesis requires both complex and realistic models of real-world light sources and efficient rendering algorithms to deal with them. In this paper, we describe a processing pipeline for dealing with complex light sources from acquisition to global illumination rendering. We carefully design optical filters to guarantee high precision measurements of real-world light sources. We discuss two practically feasible setups that allow us to measure light sources with different characteristics. Finally, we introduce an efficient importance sampling algorithm for our representation that can be used, for example, in conjunction with Photon Maps.

Application of Self-Organisation Neural Network for Direct Shape from Shading

In this paper, a supervised self-organisation Neural Network (NN) for direct shape from shading is developed. The structure of the NN for the inclined light source model is derived based on the maximum uphill direct shape from shading approach. The major advantage of the NN model presented is the parallel learning or weight evolution for the direct shading. Here the proved convergent learning rule, the rate of convergence and a zero initialisation condition are shown. To increase the rate of convergence, the momentum factor is introduced. Furthermore, the application of the network on IC (Integrated Circuit) component shape reconstruction is presented.

Light measurements of high-luminance LEDs

The achievements of modern optoelectronics have resulted in the widespread use of light-emitting diodes (LEDs) in products designed to visualize information, especially in light devices for use in road-safety systems. These developments highlight the importance of metrological support for measurements of the photometric characteristics of semiconductor light sources. A standard light-source model based on Corvette Light Corporation high-luminance LEDs has been created and studied. The high-luminance LEDs were manufactured to a unique design using planar technology. The results of the study demonstrate the stability of the metrological characteristics of the LED-based standard source.

Shape from shading for multiple light sources

Many shape recovery algorithms—in particular, shape from shading (SFS)—are based on a point source at infinity or a uniform hemispheric source. It will be convenient and useful if we can perform SFS under indoor lights that may be spherical, cylindrical, or flat (ceiling lights) in shape in an uncontrolled environment. As a first step toward this goal we propose a light source model for each of the above shapes for performing SFS. In this study we give the derivation of the rectangular, spherical, and cylindrical light source models. In indoor environments the positions (usually on the ceiling or walls) of the light sources are known. Assuming that the target object is small relative to the distances from the sources, we have derived a reflectance map for the Lambertian surface of an object under a mixture of light sources of the above shapes. Hence the shape recovery can be performed by using the SFS technique. This is a significant step toward the application of SFS in uncontrolled practical environments under household or office lighting. This technique of shape recovery is verified by many examples of simulations and real experiments, and the results are good.

Shape recovery of specular objects from multiple lights

This paper describes the method of shape recovery of specular objects illuminated by multiple light sources by pattern recognition. In this method, a three-dimensional shape is recovered from an epipolar plane image (EPI) of a rotating image. The highlight reflected from an object has a traveling characteristic corresponding to the surface profile of the object. The highlight appears in EPI as image speed. Therefore, the three-dimensional shape can be quantitatively recovered by tracing the locus of the highlight on EPI if the relationship among the shape of the object, light source, direction of view, and highlight is equated. In this study, the relationship among the object shape under illumination from multiple light sources, direction of view, and highlight is equated in order to quantitatively recover the cross-sectional view of a columnar object. In addition, three-dimensional shape recovery of a general object is accomplished by introducing the light source model of a cone-shaped illumination plane. Finally, in order to show the validity of this method, the experimental result on the recovery of specular objects and its evaluation will be described.

Methodologies and Practices for Designing Efficient Light Source Reflectors

This article highlights the major factors and considerations required to efficiently collect and redirect the flux from a light source. A discussion of light source models, measurement techniques, and units is presented, followed by a discussion of several unique reflector designs.

Lighting Controls for Computer Cinematography

Lighting is an essential component of visually rich cinematographic images. However, the common computer graphics light source models, such as a coneshaped spotlight, are not versatile enough for cinematographic-quality lighting. In this paper we describe the controls and features of a light source model for lighting computer graphics films. The model is based on generalized light cones, emphasizing independent control over the shape and texture of lights and shadows. While inspired by techniques of real-world cinematography, it is tailored to the needs and capabilities of computer graphics. The model has been used successfully in production over the past few years, to light many short works and the movie Toy Story.

General near‐zone light source model and its application to computer‐automated reflector design

The goal of this work is to develop a general light source model that is physically accurate, intuitively descriptive, computationally convenient, and applicable to real sources. It solves two major problems in illumination optics: near zone general extended light source charac- terization for accurate image rendering and ray tracing, and computer- automated reflector design using the resulting near-zone model. The main approach is to combine measurements with Fourier analysis, using judiciously chosen coordinate systems and orthogonal fitting functions. This has several advantages over standard ray tracing: it provides for natural data compression and interpolation; it bypasses the problem of computing the radiance distribution of a real source by using actual pin- hole CCD camera measurements; and it eliminates the computationally intensive ray-filament intersection problem by transforming the source into an equivalent nonuniform spherical radiator. A method for treating the occlusion of rays by the extended filament, with only spherical inter- section calculations, is also discussed. The application of the method is illustrated by the problem of designing a smooth specular reflector to cast a desired intensity distribution on a distant screen for a given source. The problem becomes a straightforward numerical optimization of the perturbations to a base reflector shape. An algorithm to provide a first guess for the perturbations based on the shape of the image perim- eter is also described. © 1996 Society of Photo-Optical Instrumentation Engineers. Subject terms: near-zone light source model; computer-automated reflector de- sign.

Light-Source Modeling Using Pyramidal Light Maps

The diversity of lighting arrangements and fixtures in everyday life allows us great creative and functional control over the appearance of our environments. In computer graphics, the lack of realistic models of light sources does not permit the same level of control. To model a light source, one must (at least) be able to specify its geometry and its spatial intensity distribution. We describe a system that permits the interactive specification of point, linear, and area light sources having arbitrary and variable spatial intensity distributions across their domains. A continuous distribution of an extended light source is created by interpolating a set of sample distributions that are interactively placed on the light source. Rendering is accomplished by resampling the light source at a variable resolution. To speed up rendering, a pyramidal representation of the light source is created, allowing the dynamic selection of the resampling rate. We describe the theory, design, and implementation of our light-source modeling system. Pyramidal light-source models can be used in rendering environments such as conventional scanline or ray-tracing renderers, or renderers with programmable shaders.