Bidirectional Scattering Distribution Function Research Articles

Image degradation due to surface scatter in the presence of aberrations

Image analysis in the presence of surface scatter due to residual optical fabrication errors is often perceived to be complicated, nonintuitive, and achieved only by computationally intensive nonsequential ray tracing with commercial optical analysis codes such as ASAP, Zemax, Code V, TracePro, or FRED. However, we show that surface scatter can be treated very similarly to conventional wavefront aberrations. For multielement imaging systems degraded by both surface scatter and aberrations, the composite point spread function is obtained in explicit analytic form in terms of convolutions of the geometrical point spread function and scaled bidirectional scattering distribution functions of the individual surfaces of the imaging system. The approximations and assumptions in this formulation are discussed, and the result is compared to the irradiance distribution obtained using commercial software for the case of a two-mirror telescope operating at an extreme ultraviolet wavelength. The two results are virtually identical.

Bidirectional scattering distribution function by screen imaging synthesis

Light-emitting diodes are common light sources in modern lighting. The optical distribution of an LED package and the bidirectional scattering distribution function (BSDF) of diffusing optical components are important factors in lighting design. This paper proposes an innovative method of measuring both the optical distribution of LEDs and BSDF quickly. The proposed method uses a 2-D screen and a camera to capture the illumination on a screen, and acquires the whole-field optical distribution by synthesizing the images on the screen in different angles. This paper presents theoretical calculations and experimental results demonstrating the construction of the BSDF.

LCD 백라이트용 렌티큘라 렌즈필름의 광구조 최적화에 관한 연구

The optical performance of LLF(Lenticular Lens Film)-based backlight was studied by using optical simulation as functions of the aspect ratio and the refractive index of lenticular lenses. In order to perform reliable simulation, the BSDF(bi-directional scattering distribution function) of the scattering dots on the bottom surface of the light guide plate was obtained as a superposition of the Lambertian and the elliptic Gaussian distribution components by comparing the experimental results and the simulation for the luminance distribution on the light guide. Based on this approach, an appropriate BSDF of the scattering dots of the light guide was constructed. The resultant values of the optimized aspect ratio and the refractive were found to be 1.25 and 1.65, respectively. In spite of the hybrid aspects of LLF incorporating both diffusing and collimating functions, the optical performance, in particular the on-axis luminance of LLF-based backlight was inferior by about 20% compared to that of conventional backlights adopting one prism film. However, the combination of two lenticular lens films resulted in comparable luminance gain as well as smooth decrease in the luminance with the viewing angle without exhibiting any side lobes.

Simulating the Daylight Performance of Complex Fenestration Systems Using Bidirectional Scattering Distribution Functions within Radiance

We describe two methods which rely on bidirectional scattering distribution functions (BSDFs) to model the daylighting performance of complex fenestration systems (CFS), enabling greater flexibility and accuracy in evaluating arbitrary assemblies of glazing, shading, and other optically-complex coplanar window systems. Two tools within Radiance enable a) efficient annual performance evaluations of CFS, and b) accurate renderings of CFS despite the loss of spatial resolution associated with low-resolution BSDF datasets for inhomogeneous systems. Validation, accuracy, and limitations of the methods are discussed.

强光辐照下主镜表面散射引起的视场内杂光分布

Light scattered from the imperfect surface of a primary mirror in a reflective optical system will result in the in-field stray light and reduce the image contrast.This paper presents a simple method to process the scattering of the primary mirror.A Harvey Bidirectional Scatter Distribution Function(BSDF) model is used to characterize the angular distribution of scattered light from the mirror,and the scattering distribution at the focal plane of the primary mirror is derived.The characteristic radius centered by the image point can be achieved when the intensity of scattering equals that of diffraction.It is found that for the given optical system,the characteristic radius only depends on the scattering characteristic of the primary mirror.The intensity distribution at the focal plane is divided into two regions by the characteristic radius.The intensity of diffraction is larger than that of scattering intensity,which makes the dominant contribution to the saturation effect when the distance from the image point is less than the characteristic radius,conversely,the scattering is the main factor to the saturation effect when the distance from the image point is larger than the characteristic radius.For a primary mirror with a focal length of-757 mm,an radius of 115 mm and the rms roughness of 10 nm at the wavelength of 550 nm,the characteristic radius is 0.843 mm approximately.These conclusions are conductive to the analyzing and explaining of the saturation effects in an optical system irradiated by a intense light.

Light-scattering properties of a Venetian blind slat used for daylighting applications

The low cost, simplicity, and aesthetic appearance of external and internal shading devices, make them commonly used for daylighting and glare-control applications. Shading devices, such as Venetian blinds, screens, and roller shades, generally exhibit light scattering and/or light redirecting properties. This requires the bi-directional scattering distribution function (BSDF) of the material to be known in order to accurately predict the daylight distribution and energy flow through the fenestration system. Acquiring the complete BSDF is not a straightforward task, and to complete the process it is often required that a model is used to complement the measured data. In this project, a Venetian blind slat with a white top surface and a brushed aluminum bottom surface was optically characterized. A goniophotometer and an integrating sphere spectrophotometer were used to determine the angle resolved and hemispherical reflectance of the sample, respectively. The acquired data were fitted to a scattering model providing one Lambertian and one angle dependent description of the surface properties. These were used in combination with raytracing to obtain the complete BSDFs of the Venetian blind system.

On-Line Inspection of the Surface Roughness of Workpiece in Ultraprecision Machining

An in situ technique to determine the surface roughness of ultraprecision machining using optical characteristic effects is fundamental as probes are not used, which prevents contact damage on the surface. Because the plastic lens molding reprints the roughness of the mold core fabricated by machining, tool marks result in the poor surface of the plastic lens. The machined surface can reflect the input light of a green laser with a short wavelength of 532 nm. By varying the feed rate of the ultraprecision machining, several samples of the electrolyte-less nickel with different surface roughness have been examined using the green laser and the photodiode array. The distribution of the optical scattering effect of each sample under the light source of green laser is derived for prediction of the surface roughness. The results show that greater surface roughness produces more expansive distribution of light scattering. In addition, the bidirectional scatter distribution function (BSDF) of the machined surface is found to be proportional to roughness. Using the ratio of the main and the side measuring channels of the photodiode array, a suitable approach to establish the relationship between light scattering and surface roughness can be developed. The laser and the photodiode array are found to efficiently predict the surface roughness of the ultraprecision machined electroless nickel.

Phosphor-converted LED modeling by bidirectional photometric data

For the phosphor-converted light-emitting diodes (pcLEDs), the interaction of the illuminating energy with the phosphor would not just behave as a simple wavelength-converting phenomenon, but also a function of various combinations of illumination and viewing geometries. This paper presents a methodology to characterize the converting and scattering mechanisms of the phosphor layer in the pcLEDs by the measured bidirectional scattering distribution functions (BSDFs). A commercially available pcLED with conformal phosphor coating was used to examine the validity of the proposed model. The close agreement with the measurement illustrates that the proposed characterization opens new perspectives for phosphor-based conversion and scattering feature for white lighting uses.

Image degradation due to scattering effects in two-mirror telescopes

Image degradation due to scattered radiation is a serious problem in many short-wavelength (x-ray and EUV) imaging systems. Most currently available image analysis codes require the scattering behavior [data on the bidirectional scattering distribution function (BSDF)] as input in order to calculate the image quality from such systems. Predicting image degradation due to scattering effects is typically quite computation-intensive. If using a conventional optical design and analysis code, each geometrically traced ray spawns hundreds of scattered rays randomly distributed and weighted according to the input BSDF. These scattered rays must then be traced through the system to the focal plane using nonsequential ray-tracing techniques. For multielement imaging systems even the scattered rays spawn more scattered rays at each additional surface encountered in the system. In this paper we describe a generalization of Peterson's analytical treatment of in-field stray light in multielement imaging systems. In particular, we remove the smooth-surface limitation that ignores the scattered-scattered radiation, which can be quite large for EUV wavelengths even for state-of-the-art optical surfaces. Predictions of image degradation for a two-mirror EUV telescope with the generalized Peterson model are then numerically validated with the much more computation-intensive ZEMAX® and ASAP® codes.

P‐67: Simulation of Backlight Using Bidirectional Scattering Distribution Function

AbstractBSDF (Bidirectional Scattering Distribution Function) has been used in order to predict exact optical characteristic of BLU (Backlight Unit). BSDF implies real scattering characteristics, and measured using test equipment of Goniometer type and compared simulation results with measuring data. Simulation was performed for direct‐type LED BLU and CCFL BLU by applying BSDF for diffuser sheet, diffuser plate, and reflector. Accuracy of total flux and luminance, viewing angle, image, etc. was increased and simulation result was obtained in a short time using BSDF assuming multiple sheets as one sheet.

An optical simulation algorithm based on ray tracing technique for light absorption in thin film solar cells

Solar cells, especially thin film solar cells, utilize rough surfaces actively in order to improve light trapping efficiency. In this study, we propose a new optical simulation method, which is capable of taking into consideration the realistic surface and interface morphology. The proposed simulation algorithm is based upon a non-sequential ray tracing technique, and direct calculation of the optical absorption energy is performed by separating the light passing through medium into the coherent part and the incoherent part in the course of non-sequential ray tracing throughout the whole region of solar cell structure. It was shown that the new method can give more accurate estimation of the absolute absorption energy in the individual layer when applied for a thin film Si solar cell structure with rough surface of bidirectional scattering distribution function. Furthermore, the proposed algorithm was proved to be very effective in analyzing solar cells with complex geometry like concentrator photovoltaic system, which necessitates the combination of coherent and incoherent calculation.

Development of a panchromatic acrylamide-based photopolymer for multicolor reflection holography

We present the development of a panchromatic acrylamide-based photopolymer (ABP) for holographic recording application. The scattering of the recording medium was characterized by measuring the bidirectional scattering distribution function. The dynamic range in the reflection mode of recording was evaluated by measuring the diffraction efficiencies of the holographic gratings recorded individually at 633 nm, 532 nm, and 473 nm wavelengths at spatial frequencies of 4200 lines/mm, 5000 lines/mm, and 5700 lines/mm, respectively. Spectral characterization of the reflection gratings, recorded using a combined single red-green-blue (RGB) beam, was carried out, and the reconstructed wavelengths were monitored and compared with the recording wavelengths. The recorded and the reconstructed wavelengths were plotted as points on the International Commission on Illumination (CIE) chromaticity diagram in order to reveal shifts due to material shrinkage in the corresponding RGB wavelengths. Finally, reflection holograms of an object were successfully recorded at all the three primary wavelengths. The results represent a strong confirmation that this ABP can be used as a panchromatic recording material and can be employed in future commercial holographic applications.

36.4: Modeling Diffuse Components by Bidirectional Scatter Distribution Function for LCD Applications

AbstractThis paper presents a methodology for including the photometric raw data sets into the diffuse illumination in display system. The method is based on computing the luminance distribution on the outgoing side of diffusing elements from measured bidirectional scattering distribution functions (BSDFs). The calculation procedure includes the linear superposition and the feedback. As an application example, the method is verified by a commercially available diffusing sheet illuminated by a 32‐inch backlighting module. Close agreement (correlation coefficient = 98.6%) with the experimental measurement confirmed the validity of the proposed procedure.

5.2: Approaches to Virtual Product Development in LCD Business

AbstractIn the process to build up the complicated system for a LCD backlight unit, a panel and their module assembly, the use of physical prototype has many drawbacks in terms of cost and lead‐time. The virtual prototyping platform, EzOptics we developed in the cooperative work, provides the way of working where the LCD design and optical analysis activities can be developed in the early product development stages. The work being described here permits that a designer analyses the optical characteristics of a LCD module with a panel. In the LCD industry this must be the first system by which the virtual prototyping of LCD can substitute the physical prototype. The system allows a virtual prototype with a full size scale LCD backlight unit and panel modelling without any limitations of the size and shape. The result of the simulation also guarantees the accuracy by supporting the bidirectional scattering distribution functions (BSDF) to define the scattered light propagation over the optical components, and the expert knowledge is provided for more comprehensive, quick and user‐friendly virtual prototype modelling.

Using digital cameras as quasi-spectral radiometers to study complex fenestration systems

This work discusses the use of digital cameras fitted with absorption filters as quasi-spectral radiometers. By filtering incident light into selected wavelength intervals, accurate estimates of radiances can be made for unknown spectra. This approach is being employed as part of a new video-projection goniophotometer to study the properties of angularly and spectrally selective complex fenestration systems. Complex fenestration systems are increasingly being used to distribute solar radiation purposefully in buildings. They can be utilized to optimize energy performance and enhance daylighting. Radiance estimates from calibrated digital cameras enable the assessment of quasi-spectral, bi-directional scattering distribution functions of total radiance transmitted or reflected by a fenestration system over desired wavelength intervals. A silicon and an indium gallium arsenide digital camera are used to enable measurements across a 380 to 1700 nm wavelength interval.

An iterative model of diffuse illumination from bidirectional photometric data

This paper presents a methodology for including the photometric raw data sets into the diffuse illumination design process. The method is based on computing the luminance distribution on the outgoing side of diffusing elements from measured bidirectional scattering distribution functions (BSDFs). The model is limited to specimens that create rotationally symmetric scattering distribution. The calculation procedure includes the linear superposition and the correcting feedback. As an application example, the method is verified by a commercially available diffusing sheet illuminated by a 32-inch backlighting module. Close agreement (correlation coefficient = 98.6%) with the experimental measurement confirmed the validity of the proposed procedure.

用于BSDF测量角度自动补偿装置设计及实验研究

When using a single reference to measure the bi-directional scattering distribution function (BSDF), the incident zenith angle of the tested sample must be identical to that of the reference. In order to get the hemisphere space scattering characteristic on the sample surface, usually a motor drives the sample tilting, then the incident zenith angle is changed and needs to be the compensated by another motor. We mathematically deduce the expression of compensation angle when the incident zenith angle is changed by the rotation of motor. After the incident angle is compensated, the scattering zenith angle and azimuth angle are deduced too. The uncertainty of the system is 0.75%. Scattering measurements are performed on copper sample with visible light under different temperatures.

Optical characterization of fritted glass for architectural applications

Fritted glass is commonly used as a light diffusing element in modern buildings. Traditionally it has been used for aesthetic purposes but it can also be used for energy savings by incorporating it in novel daylighting systems? To answer such questions the light scattering properties must be properly characterized. This paper contains measurements of different varieties of fritted glass, ranging from the simplest direct-hemispherical measurements to angle-resolved goniometer measurements. Modeling the light scattering to obtain the full bidirectional scattering distribution function (BSDF) extends the measured data, making it useful in simulation programs such as Window 6 and Radiance. Surface profilometry results and SEM micrographs are included to demonstrate the surface properties of the samples studied.

Design of an instrument for measuring the spectral bidirectional scatter distribution function

The spectral bidirectional scatter distribution function (BSDF) offers a complete description of the spectral and spatial optical characteristics of a material. Any gloss and color measurement can be related to a particular value of the BSDF, while accurate luminaire design with ray tracing software requires the BSDF of reflectors and filters. Many measuring instruments, each having particular advantages and limitations, have been reported in the literature, and an overview of these instruments is included. A measuring instrument that allows for an absolute determination of the spectral BSDF with a full three dimensional spatial coverage in both reflectance and transmittance mode, a broadband spectral coverage, a large dynamic range, a reasonable acquisition time, and a large sample illumination area is presented. The main instrument characteristics are discussed, and the measurement capabilities are illustrated.

Dual scattering approximation for fast multiple scattering in hair

When rendering light colored hair, multiple fiber scattering is essential for the right perception of the overall hair color. In this context, we present a novel technique to efficiently approximate multiple fiber scattering for a full head of human hair or a similar fiber based geometry. In contrast to previous ad-hoc approaches, our method relies on the physically accurate concept of the Bidirectional Scattering Distribution Functions and gives physically plausible results with no need for parameter tweaking. We show that complex scattering effects can be approximated very well by using aggressive simplifications based on this theoretical model. When compared to unbiased Monte-Carlo path tracing, our approximations preserve photo-realism in most settings but with rendering times at least two-orders of magnitude lower. Time and space complexity are much lower compared to photon mapping-based techniques and we can even achieve realistic results in real-time on a standard PC with consumer graphics hardware.