To investigate the legibility and visual comfort of LED traffic signs, an ergonomic experiment is performed on four custom-designed LED traffic signs, including three self-luminous ones as LED lightbox, LED backlight and regional LED backlight, and one non-self-luminous sign with external LED lighting. The four signs are hanged side-by-side and evaluated by observers through questionnaires. The signage dimension is one-sixth of the real freeway traffic signs, and the observation distance is 25 m. The luminance of three self-luminous signs is 216 cd/m<sup>2</sup>. The illuminance of external LED lighting is 400 lux on the traffic sign. The ambient illuminance is 2.8 and 6.0 lux in two rounds. The results show that self-luminous traffic signs provide superior legibility, visual comfort and user preference than the non-self-luminous one. Among the three self-luminous signs, regional LED backlight is most susceptible to the ambient illumination. LED lightbox has significantly better preference score than LED backlight under darker ambient lighting. Only LED lightbox has significantly better visual comfort than external LED lighting in the brighter environment. Based on the four LED traffic signs evaluated in this study, we suggest LED lightbox as the prior choice. Further investigations on the effect of ambient illumination and other designs of self-luminous traffic signs are in progress.
Due to the worldwide portable devices and illumination technology trends, researches interest in laser diodes applications are booming in recent years. One of the popular and potential LDs applications is near-eye display used in VR/AR. An ideal near-eye display needs to provide high resolution, wide FOV imagery with compact magnifying optics, and long battery life for prolonged use. However, previous studies still cannot reach high light utilization efficiency in illumination and imaging optical systems which should be raised as possible to increase wear comfort. To meet these needs, a waveguide illumination system of near-eye display is presented in this paper. We focused on proposing a high efficiency RGB LDs light engine which could reduce power consumption and increase flexibility of mechanism design by using freeform TIR reflectors instead of beam splitters. By these structures, the total system efficiency of near-eye display is successfully increased, and the improved results in efficiency and fabrication tolerance of near-eye displays are shown in this paper.
Recently, there is an interest in the laser-based white light source for illumination and display applications. The laser-based
white lights inherently have much higher luminance than the corresponding LEDs. Moreover, laser diodes are often more
efficient when operating at higher current densities and are with smaller form factors, which may outperform LEDs in the
future. Based on this, in this paper, we combine the design of the light guide and reflective type remote phosphor structures
in order to improve the overall performance of the laser-based white light source. In addition, these well-designed white
light sources will provide the more flexible architecture for designing the subsequent lighting system. With the introduction
of the innovative design for the laser-based illumination system, multiple applications incorporating laser and remote
phosphor elements for improving lighting efficiency and quality were obtained.
This paper presents the illumination uniformity study on the reading area for a well-designed reflective LED lighting module by placing diffuser plate with optical simulation technique. The investigation for the performance of intensity and uniformity was performed and discussed by changing various curvatures of diffuser plate with and without microstructures to reflect and spread light. Due to the development of microstructures on diffuser plate, the light intensity distribution was uniformed on the reading area. In addition, the diffusion and spreading effect from a curved surface with microstructures was better than that without curvature or microstructures. The illumination uniformity was strongly influenced by the shape of microstructure on reflective diffuser plate. The optimal design with cylinder-shape microstructure on the lampshade had better performance in this study; the illumination uniformity was increased from 17 % to 69 % and the enhancement was 75 %. A well-designed diffuser plate model was fabricated by CNC machine and the deviations between experimental and simulated illumination results for maximum intensity and uniformity were 7.4 % and 8.7 %, respectively.
Proc. SPIE. 9524, International Conference on Optical and Photonic Engineering (icOPEN 2015)
KEYWORDS: Light sources, Light emitting diodes, Visualization, Calibration, Image segmentation, Inspection, Optical inspection, Light sources and illumination, High dynamic range imaging, RGB color model
Glare is caused by both direct and indirect light sources and discomfort glare produces visual discomfort, annoyance, or loss in visual performance and visibility. Direct glare is caused by light sources in the field of view whereas reflected glare is caused by bright reflections from polished or glossy surfaces that are reflected toward an individual. To improve visual comfort of our living environment, a portable inspection system to estimate direct glare of various commercial LED modules with the range of color temperature from 3100 K to 5300 K was developed in this study. The system utilized HDR images to obtain the illumination distribution of LED modules and was first calibrated for brightness and chromaticity and corrected with flat field, dark-corner and curvature by the installed algorithm. The index of direct glare was then automatically estimated after image capturing, and the operator can recognize the performance of LED modules and the possible effects on human being once the index was out of expecting range. In the future, we expect that the quick-response smart inspection system can be applied in several new fields and market, such as home energy diagnostics, environmental lighting and UGR monitoring and popularize it in several new fields.
Nowadays, light emitting diodes (LEDs) have been widely used in backlight module for display technology. Most of researches tend to improve optical performance in specific applications, such as sufficient efficiency, desired intensity distribution and high illuminance uniformity. However, most of phosphor converted white LEDs have the problem of inducing impure white light. The undesired phenomenon of yellow ring or blue ring becomes more serious through incorrect secondary optical design. In this paper, we emphasize on enhancing the spatial color and illuminance uniformity of LED direct-lit backlight using nonimaging achromatic lens design. We propose a new design method to re-distribute and uniform the ratio of blue and yellow light on the target surface. Moreover, we further apply it in direct-lit LED backlight lens design, in which the uniformity of illuminance on the out coupling surface can be as much as 83.7% and the color uniformity triangleu'v') is improved to 0.0039. Therefore, the result of high color and illumination uniformity can be achieved simultaneously.
This research develops a precise hybrid optical micro-component (PHOMC) that includes polymer and glass materials.
Although glass offers better anti-thermal, anti-environmental, anti-scraped, anti-corrosive, and optical properties than
polymer materials do, glass materials are difficult to fabricate for microstructures. This research describes the fabrication
of a PHOMC, which retains the advantages of glass materials; in addition, the cost of microstructure polymers is lower
than for glass. In this study, polymers with micro sine waves can change the spot light intensity from a Gaussian
distribution to a line with uniform distribution. The glass base can protect the PHOMC to avoid damage from the
environment. First, the sine wave was designed using optical design software to change the light profile. A precise
diamond-turning technique was used to fabricate a mold with a sine-wave profile. A glass plate was used for the base of
the PHOMC. During the heating process, a thermosetting polymer was formed to match the sine-wave profile, and
covered the glass base. The PHOMC is 10 mm in diameter, and a sine wave with 100 μm in amplitude and 6.283 in
angular frequency was obtained. The surface profile of the PHOMC was evaluated using an ultra-precise laser confocal
microscope. Processing parameters, such as the forming temperature, are discussed in this paper. The PHOMC with the
sine wave that was developed in this study can generate a reference straight line for use in alignment, machine vision
systems, construction, and process control.
Research interests on sunlight applications are booming in recent years, due to the worldwide green-energy trends. Either using PV cells to store sunlight then convert to electricity, or to use sunlight for direct illumination source are among the many research projects which deserve investigation.<p> </p>In this research, we focus a design combined the above two features together: direct sunlight illumination, and store the sunlight for later usage. Our design structure is as follows: 1. On the surface of outer layer, we use the liquid-prism structure to increase the angle tolerance range of solar concentrator; 2. Combine the micro structure of the solid-state prism and aspheric surfaces to produce a planar light guide structure, which compresses the plane light source into line light source, then guide the light into solar cells area; 3. Design a light switch using the liquid-prism of inside layer, and guides the sunlight into solar cells channel or indoor illumination channel.<p> </p>We apply it in the NLIS<sup>®</sup> developed at NTUST, not only retain the advantages of the static concentrator modules, but also eliminate the complex procedure of transmitting and emitting, reduce the loss and cost of energy transfer.
Sunlight is the most environmental-friendly energy. Through the Natural Light Illumination Systems (NLIS<sup>® </sup>),
we can guide sunlight indoors to use. However, due to the construction cost of the NLIS<sup>® </sup>, the most cost is spent on the optical fiber. Therefore we intend to design an element that can re-shape the beam from the SunLego<sup>reg; </sup> to be narrower, where SunLego<sup>® </sup> is the building unit of NLIS<sup>® </sup>for light collection. The element consists of two functional optical structures: the first structure is to convert light from SunLego<sup>® </sup> to parallel beam, technically, is to convert stray light to parallel. We design the first structure based on free form principle. The second is a fan-shaped structure, which is to reduce the light transmission area , this design is based on the E'tendue principle. The reduction of area means we can use smaller fiber for later light transmission, which is crucial to reduce material cost.
The concept of the remote phosphor is proven to be one of the effective solutions for improving luminous efficacy of pc-WLEDs by solving the problem of phosphor thermal and scattering loss. However, most of them need to use larger packaging design to enhance their performance. Such development is adverse to market trends, which also resulted in higher manufacturing costs and the difficulties in luminaire design. In this paper, we present the analysis of pc-WLEDs as the function of the packaging size and figure out its limitation, so that we can apply to reduce the device size but keep the luminous efficacy as high as possible.
Based on Monte Carlo ray tracing we present a study of GaN die with a reflective layer coated on a p-GaN surface inside the light guide as a planar light source. We simulated the lights extracted from the GaN die implanting pyramid microstructure on the top surface of sapphire or on the top surface of p-GaN. Micro pyramid array with different slanted angle from 5<sup>0</sup> to 85<sup>0</sup> is shown to effectively improve the light extraction efficiency. In addition, the pattern sapphire substrate with slanted angle of ten degrees is found to be an effective way to increase the lateral directionality than the surface texture.
In this paper, based on Monte Carlo ray tracing we simulate light extraction efficiency and directionality of the light
pattern of GaN LEDs implanted with micro-pyramid structure with or without lens encapsulation. We have shown that
micro-pyramid structures at some specific slanted angles in the LEDs are useful to increase effective flux utilization
through enhancement of both the directionality and light extraction efficiency.
Light extraction efficiency is important to the brightness of LEDs. In this study, various texturing and roughing
schemes were formed on the surface or interface of InGaN-based LED structure grown on sapphire substrate to
investigate their effects. Throughout the research, temperature-dependent PL measurement was used to calculate the
internal quantum efficiency so as to derive the light extraction efficiency. The light extraction efficiency is around 60
to 65% while the epitaxy and substrate are flat. On the other hand, the light extraction efficiency reaches an optimal
value of around 85% while the p-GaN surface is textured and the substrate is patterned. However, for LED having
only one-side surface texturing structure optimized on either p- or n-side, the light extraction efficiency can be
already as high as 75 to 80%. Methods for further enhancement, such as use of ZnO nanorod on chip surface, were
A direct or bottom LED backlight is a key concept in large area LCD displays because it does not use a light guide, is
flat, and is easy to assemble. In this paper, a method of luminance management for a bottom LED backlight is proposed
and demonstrated. We analytically calculate both the power consumption and brightness uniformity in function of: screen
brightness, screen size, backlight thickness, transmittance of the LCD panel, reflective cavity efficiency, gain and cone
angle of enhancement films, LED array configuration, and the average luminous flux and radiation pattern of a single LED.
Moreover, a 42-inch LCD television with this backlight design approach is made and demonstrated. The bottom backlight
incorporates an array of RGGB 4-in-1 multi-chip LEDs within a highly reflective box behind a diffuser and a dual
brightness enhancement film. We predict with an accuracy of 94% the brightness uniformity and with 96% the luminance
Optical analysis of the light extraction based on Monte-Carlo ray tracing in high-efficiency GaN-based LEDs
with use of textured structure is presented. The simulation indicates that the introduction of micro pyramid array with
slanted surfaces can effectively improve the light extraction efficiency. In addition, the light extraction of three types
of LED with or without an epoxy lens is analyzed, where the patterned substrate with pyramid structure arrays is
shown most effective way to increase light extraction efficiency in an encapsulated LED with an epoxy lens.
Proc. SPIE. 6342, International Optical Design Conference 2006
KEYWORDS: Light sources, Light emitting diodes, LED lighting, Scattering, Light scattering, 3D modeling, Monte Carlo methods, Distance measurement, Light sources and illumination, Charge-coupled devices
In this paper, we propose a novel LED modeling algorithm for precise 3-D light pattern simulation. Normalized cross correlation is proposed to to verify the validity of the simulation in 1-D intensity pattern as well as 2-D irradiance pattern in various mid-field distances. The model is demonstrated to obtain more than 98% in normalized cross correlation between the simulation light pattern and experimental measurement for a TIP LED emitter by Lumileds.
We proposed a combo design of pick-up head used prism to shorten the geometrical size and reduce the optical components. We apply a rhomboid beam splitter to separate two diodes in the design for the optical pick-up head of DVD and HD-DVD.
In this paper, based on the Monte-Carlo ray tracing simulation we present the study of the light extraction efficiency of GaN-based LEDs as a function of the position of the light source over the active layer with several parameters, including chip dimensions, absorption coefficients and package. Besides, the light extraction efficient characteristic of a ThinGaN LED is studied.
An optical model for simulating light extraction efficiency of a GaN-based LED chip is presented. We propose the introduction of a periodic sharpening structure on the interface between the sapphire and the n-GaN of a GaN-based LED to obtain as high as 78% light extraction efficiency.
We propose a design of a compact HD-DVD pickup head, where a lensed penta-prism is used to replace the mirror and the collimating lens in a conventional one to shorten the geometrical size but keep the whole optical path length unchanged.