Irradiance formations in hollow straight light pipes with square and circular shapes

We investigated, both analytically and numerically, the irradiance formation of an asymmetrically located Lambertian light source in hollow straight light pipes with square and circular shapes. The uniform irradiance distribution in a square light pipe and hot-spot localization in a circular light pipe were examined and determined semianalytically. Typical factors of influence, such as light-pipe length, width, and source size, were identified with extensive simulation. When the ratio of light-pipe length and width was less than 0.5, the deviation from uniformity could be more than 20%. But once the source size was large enough (approximately half of the incident port), such that the Lambertian characteristics of the source dominated the irradiance distribution, the uniformity deviation was reduced. Furthermore, a quantity of root-mean-square circular differences was defined in order to identify the shape deformation of the light pipe; it was found that the peak value of the hot spot decreased exponentially with the deformation scale. The influence of nonperfect reflectivity of the pipe wall on irradiance formation was also examined for a square light pipe; when the reflectivity is larger than 90%, the difference in uniformity is less than 10% and uniform irradiance remains, provided that the ratio of light-pipe length and width is larger than 1; even the source is located asymmetrically.     

Toward the Lambertian limit of light trapping in thin nanostructured silicon solar cells

We examine light trapping in thin silicon nanostructures for solar cell applications. Using group theory, we design surface nanostructures with an absorptance exceeding the Lambertian limit over a broad band at normal incidence. Further, we demonstrate that the absorptance of nanorod arrays closely follows the Lambertian limit for isotropic incident radiation. These effects correspond to a reduction in silicon mass by 2 orders of magnitude, pointing to the promising future of thin crystalline silicon solar cells.     

Cyclic tearing and crack growth in circumferentially cracked straight pipes

Earthquake load, which is cyclic in nature and of short duration, is the main design basis accident load for designing the primary heat transport (PHT) piping components of Nuclear Power Plants. Adequate protection of piping components from the effects of earthquake requires detailed knowledge of strength and deformation characteristics of the components and assemblies making up the piping system. Fracture behaviour of 23 pipes was studied by conducting cyclic tests under four‐point bending. Fifteen pipes were of carbon steel (SA333 Grade 6) of 219 mm, 324 mm and 406 mm ODs and eight pipes were of stainless steel (AISI Type 304LN) of 168 mm OD with through‐wall circumferential crack. Six pipes were tested under displacement control and the rest under load control. The effect of various parameters such as location and size of initial crack in base metal and weld metal, cyclic load range and displacement increment on crack growth and number of cycles for failure was investigated. The investigations showed significant reduction in the fracture resistance under cyclic loading conditions. Crack growth equations have been proposed for carbon steel pipes with and without weld under cyclic tearing.     

Assessing the accuracy of fatigue life in surface‐cracked straight pipes

The demonstration of leak before brake (LBB) based on fracture mechanics requires information on the initial size of a defect, initiation of crack growth from the inherent defect and subsequent crack growth rates. In the present paper the prediction methodologies have been tested for three different full scale pipes geometry experimentally tested data. The prediction accuracy of two SIF solutions available in the literature has also been judged. The effect of fatigue crack closure and corrections needed in the numerical prediction methodology using FEM have also been included. The results showed that the FEM could fairly predict the fatigue crack initiation and crack growth life of full‐scale piping components having a constant depth crack profile.     

Transmittance of skew rays through metal light pipes

The transmittance of skew rays through metal light pipes is examined with ray tracing. The transmittance with respect to pipe length is compared with analytical approximations and with experimental data. The effects of pipe material, pipe shape, wavelength of the incident light, distribution of the incident light, and maximum angle of incidence on transmittance are examined. The transmittance is shown, in general, not to be exponential with respect to pipe length. Additionally, the effect on transmittance of elbows and gaps in a pipe is investigated.     

Application of high-efficiency light sources

The ever increasing development and marketing of lamps has imposed a greater need upon the lighting designer to understand the different operating characteristics of these various lamps and their application in lighting designs. Luminous efficacy must be treated with great care when used to compare light sources of different types, as it conveys no information about variation of light output with age, colour appearance, colour rendering, mortality or flexibility of control     

高均匀度直下式LED平板灯设计

目的:设计兼顾照明均匀度和厚度的直下式平板灯光学配光系统。方法:基于矢量折射反射定律和曲面微分几何原理,推导自由曲面的偏微分方程,并基于几何构型法的多自由曲面的数值构建方法,设计用于直下式LED平板灯的双自由曲面透镜。结果:将该透镜用于阵列照明,LED芯片间距为60 mm,数量降低9倍,在距高比为3∶1时实现大面积均匀照明平板灯的薄型化设计,照明均匀度达到93.4%。结论:平板灯的厚度下降为传统灯具的1/3,有效提高了直下式平板灯的性价比。     

Generation of uniform light by use of diode lasers and a truncated paraboloid with a Lambertian scatterer

Uniform illumination was generated by use of a large number of diode laser emitters and a single nonimaging paraboloid with a Lambertian scatterer in the truncation plane. Laser light traverses a path toward the Lambertian surface and back by total internal reflection. An overall efficiency of 69% was demonstrated. Improvements that would increase the efficiency to more than 85% are suggested. The illuminated area is circular, with 14-mm diameter. The spatial nonuniformity of the beam profile is less than +/- 2%.     

Generation of propagation-invariant light beams from semiconductor light sources

We have studied the possibility of generating propagation-invariant (nondiffracting) light beams using various semiconductor sources of radiation. The propagation-invariant (Bessel) beams have been generated using cone-shaped lenses (axicones) with an apical angle of 178° and 170°, which provided beams with a central spot diameter of 100 and 10 μm, respectively. The radiation sources were represented by various types of light-emitting diodes, quasi-single-mode semiconductor vertical-cavity surface-emitting lasers and broad-stripe (100 μm) edge-emitting laser diodes. It is demonstrated that these semiconductor light sources offer a promising basis for the generation of propagation-invariant light beams in various devices (including optical tweezers) intended for manipulating micro- and nanodimensional objects.     

Using carbon-containing field-emission structures in cathodoluminescent light sources

Results of experimental and theoretical investigation of vacuum cathodoluminescent (VCL) light sources with field-electron emission from carbon-containing structures are presented. Comparative analysis of the distribution of current on the light-emitting anode surface in VCL sources of various designs has been performed. The influence of pulsed regime parameters on the VCL source brightness and efficiency has been evaluated. Promising directions in the development of VCL light sources based on planar-edge type field-emission structures are discussed.     

Comparison of sun pillars with light pillars from nearby light sources

Using a Monte Carlo method, we simulate the appearance of light pillars produced by nearby light sources and compare their appearance with simulations of Sun pillars. Photographs of light pillars are also compared with the simulations. We expand the idea of light and Sun pillars by examining the reflected-light patterns from several different known distributions of airborne ice crystals. Polarization properties of light pillars from nearly horizontally oriented plate crystals are also simulated.     

Failure analysis on weld joints between the elbow and straight pipes of a vacuum evaporator outlet

This study presents an analysis on a weld joint leakage accident between elbow and straight pipes that connect the inlet of a catalyst plant vacuum pump and the outlet of a vacuum evaporator tank. Moreover, the causes and mechanisms of material degradation are investigated by analyzing the chemical compositions and observing the microstructures with the use of a metallographic microscope and a scanning electron microscope. Energy dispersive spectroscopy was used on the test materials and corrosion products to examine the changes in the elements during material degradation. The results show that stress corrosion cracking caused the cracks and the leakage on the joints. The fracture morphologies were dominated by river cleavage and fan-shaped cleavage patterns. The existence of Cl⁻ and residual stress from the installation of the elbow pipe and the heat effect of the welding process contributed to the stress corrosion cracking.     

Scattering of light from quasi-homogeneous sources by quasi-homogeneous media

The field generated by scattering of light from a quasi-homogeneous source on a quasi-homogeneous, random medium is investigated. It is found that, within the accuracy of the first-order Born approximation, the far field satisfies two reciprocity relations (sometimes called uncertainty relations). One of them implies that the spectral density (or spectral intensity) is proportional to the convolution of the spectral density of the source and the spatial Fourier transform of the correlation coefficient of the scattering potential. The other implies that the spectral degree of coherence of the far field is proportional to the convolution of the correlation coefficient of the source and the spatial Fourier transform of the strength of the scattering potential. While the case we consider might seem restrictive, it is actually quite general. For instance, the quasi-homogeneous source model can be used to describe the generation of beams with different coherence properties and different angular spreads. In addition, the quasi-homogeneous scattering model adequately describes a wide class of turbulent media, including a stratified, turbulent atmosphere and confined plasmas.     

两种光源光通量测量方法的比较

介绍两种光源光通量测量方法：加V（λ）修正的光度计法和分光法,比较各自的特点,并分析影响光通量测量结果的因素。加V（λ）修正的光度计法测量光通量简捷、快速,但无法同时测量光色参数。随着新型光电测试技术的日益成熟,光谱辐射计性能越发完善,除了测量光源光通量,还可计算光源的色品坐标、色温、显色指数、色容差等色度参数。在CIE127中分光法被推荐为测量光源光色参数的方法。