In this paper, we investigate a circuit design to reduce light flicker from an alternating current (AC) light-emitting diode (LED) lighting system. AC LEDs in the commercial marketplace have been criticized for the light flicker that they produce. In general, light flicker is an unwelcome phenomenon in a lighting application because of the health hazards it may cause. Some solutions have been proposed to reduce flicker from light sources, but they suffer from issues such as low power factor, low power efficiency, or bulky size. Here we propose an approach that can effectively reduce light flicker from an AC LED lighting system while maintaining normal power factor and high power efficiency.
Field measurements were conducted to identify how the actual lighting environment has changed in train stations due to the aftermath of the Great East Japan Earthquake. Horizontal illuminance on the floor on the way from the platform to the exit of the station and the number of the lighted luminaires in each area of each station were measured. The measurements were conducted twice, in the summer and in the autumn 2011, to identify the continuity of electricity saving measures and the transition of the lighting environment. From the results of the measurements in the summer, it was identified that nearly 80% of the luminaires was lighted off in maximum. The results of our survey showed the possibility to lower the floor illuminance level for some areas where the passengers felt no inconvenience in walking, such as the ticket gates area and concourse.
This research focused on the development of a mercury-free light source through the use of radio frequency (RF) and microwave discharges. RF at 13.56 MHz and microwave at 2.45 GHz were applied to generate the plasma. With the use of this kind of high frequency power generator, plasma can be ignited without using the electrodes inside the chamber or discharge tube, which could significantly increase the lamp lifetime. The potential for high luminance, excellent colour rendering and environmental-friendliness makes xenon the most promising candidate as the replacement for the mercury fluorescent lamp. In this research, RF energy at 13.56 MHz was induced to the cylindrical discharge tube in order to investigate the characteristics of the xenon RF-inductively coupled plasma discharge as a light source. The luminance, spectral distribution and colour rendering index were measured. The values of the luminance and colour rendering index were comparative to the values for a conventional discharge lamp. For microwave plasma, in order to develop a planar-type lamp, surface wave plasma was applied. A few types (transverse, inclined, longitudinal) of slot antennas were tested and the lamp brightness and discharge uniformity were evaluated. The chamber window (front or rear) was coated with a three-colour phosphor from the combination of red, green and blue phosphors and the excitation effect was investigated. From phosphor coating and slot structure optimisations, lamp luminance and discharge uniformity could be improved.
Near-infrared spectroscopy (NIRS) is an efficient and non-destructive method for quantitatively analyzing ingredients in a material. However, this method requires an expensive and time-consuming process to establish a calibration model. As a consequence, once the calibration model is established, it usually is used for many other spectrometers. Then, more or less a disparity in the predicted ingredient content of the material is observed. This phenomenon is called the instrumental difference and gives a difficulty in the application of NIRS. The reason is that waveform of near-infrared (NIR) spectrum is influenced by the characteristics of the spectrometer. We examined the process of measurement and found the spectral waveform was distorted by the variation of spectral response within wavelength resolution of the spectrometer. Therefore, the large spectral response variation and low wavelength resolution causes the big waveform distortion and then the big difference of predicted value of contents. Using seven linear array spectrometers, we analyzed this distortion and evaluated the difference of the predicted value. The results coincided with the analysis. By understanding the mechanisms of instrumental difference, we can design a spectrometer with minimal instrumental difference. This result could be applied to any other spectroscopy that acquires spectral waveform by dividing the sample waveform by the reference waveform.
This study aimed at estimating the brightness of a monochromatic LED point source as perceived by the elderly and protanopes. In order to estimate the perceived brightness of the monochromatic LED point source for the elderly and protanopes, we defined an index, brightness perception efficiency, which is a ratio of perceived luminosity with spectral luminous efficiency of the elderly or protanopes to the luminosity with standard spectral luminous efficiency. The brightness perception efficiency was calculated using both the LED spectral radiant intensity defined by a peak wavelength and a full width at half maximum (FWHM) of the LED, and the spectral luminous efficiencies of the elderly in their 70s and protanopes. The brightness perception efficiency indicated that monochromatic LED point sources with a broad FWHM effectively attenuate the reduction in perceived brightness of the elderly and protanopes. It is expected that in the case of a peak wavelength of 475 nm the elderly perceive brightness equivalent to 1.6 times luminosity for the LED with a FWHM of 100 nm compared to that with a FWHM of 15 nm, and in the case of a peak wavelength of 635 nm protanopes perceived brightness equivalent to about 3 times luminosity for the LED with a FWHM of 100 nm compared to that with a FWHM of 15 nm. Based on the brightness perception efficiency, we developed an LED illumination simulator that allows the young observers with normal color vision to experience the brightness perceived by the elderly and protanopes.
This paper reports on the development of a two-dimensional (2D) optical simulator for surface mount device (SMD) light emitting diode (LED) packaging (PKG). In the early phase of the development of an LED, an optical simulator is important for designing the LED PKG; thus, we have developed a 2D optical simulator specialized for this purpose. This simulator provides an easy and simple interface for setting simulation parameters. In addition, simulations can be executed quickly because the method used by the simulator produces a result by multiplying the vertical and horizontal results from a 2D simulation. In this paper, we present simulation results showing the relative intensity distribution of the light emitting surface of a side view (SV) LED.
In planer-type optical devices such as OLED, the loss-propagating surface plasmon polaritons (SPPs) at the interface on a metallic cathode has been regarded as holding the key to the efficiency improvement. It complicates the characteristics of SPPs, however, that the existence of the classical or phenomenological surface electromagnetic (EM) propagation modes at the interface. With the aid of tracing the predecessors' prior achievements, we clarify theoretically the characteristic of surface EM modes over a comprehensive variety of a permittivity of the interfacing medium. As a result, we prove that there is a requisite in order that the surface EM excitations might be quasi independently observed in a vertical dipole radiation nearby the interface, which is non-positive real part of a permittivity of the medium interfacing to the air, such as a real metal, involving the condition for existence of SPPs.
Color rendering property (Ra) is one of the important indexes to evaluate the performance of illuminant. Controlling the light intensities for the four kinds of color LEDs (red, green, blue and white) on the portable-sized full-color LED panel, and then adding blue LED with different wavelength, the authors gained the high rendering property of Ra=96. At that time the Ra of the white LED was 87. This result concludes that it is possible to obtain superior color rendering property (Ra) even if the Ra of the white illumination alone is not high.
The authors propose a new method for tunnel illumination using LED lights. The luminous characteristics of tunnel lighting employing LED luminaires were measured in the Shiratori tunnel on the Japanese expressway. The results show that this method achieves over 0.9 of luminance uniformity. Moreover, the visual impression evaluation that was conducted using 29 subjects, shows that roads with over 0.9 luminance uniformity and luminance of 2.3 cd/m2, have equivalent or better visibility than roads with low uniformity and luminance of 3.5 cd/m2. This result suggests that the High Luminance Uniformity Method which we propose could save up to 20% of the energy used for illumination and improve safety due to higher visibility.
Commission Intemationale de l'Eclairage (CIE) published CIE 191: Recommended System for Mesopic Photometry Based on Visual Performance was published in 2010. However, it is still necessary to identify appropriate applications and make guidelines for the new mesopic photometry system. To this end, we dealt with interference between the foveal task and the peripheral task that often exists in the real driving context. Such interference often appears to exaggerate the effectiveness of short-wavelength radiation on peripheral visual performance at mesopic light levels. To address a question of how the foveal vision affects the peripheral vision for different spectral power distributions, but for the same mesopic luminance, we conducted a controlled laboratory experiment and two supplemental laboratory experiments. In these experiments, we asked subjects to perform a foveal tracking task and a peripheral target-detection task, simulating nighttime multi-tasking driving activities in mesopic light levels. Based on the results of the experiments we confirmed the Purkinje phenomena. We also found interference between the foveal task and the peripheral task (especially when the foveal task was difficult). Such interference not only impairs the foveal task performance but also reduces the peripheral responses significantly, and potentially makes the Purkinje phenomena appear to be exaggerated. This confirmed the importance of using light sources with more short-wavelength radiation for better peripheral visibility in nighttime roadway lighting applications. Such interference also suggests that the use of a simple easy task may help eliminate any effect of interference on databases to establish a unified mesopic photometry system.
The symmetrical lighting system, which is appropriate to recognize an object with silhouette vision, has been used for many years as tunnel interior lighting. The pro-beam lighting system however has an advantage to enhance visibility with reversed silhouette and has being investigated for more safe and comfortable driving in the tunnel for several years by the NEXCO group, especially to increase visibility for a preceding vehicle to prevent rear-end collisions. The pro-beam lighting with ceramic metal halide lamps was largely adapted for 70 tunnels of New Tokyo–Nagoya expressway in 2012, and further study has being made to achieve both good visibility and power efficiency with the use of LED pro-beam lighting. In this paper, the research concerning to pro-beam lighting are described such as visibility analysis of LED tunnel lighting, enhanced visibility by pro-beam, and evaluation of experimental installation by both field observations and the mathematical values of total revealing power. The evaluation of the LED pro-beam tunnel showed good visibility and power efficiency.
Recently, the demand for improvement of passenger comfort in automobiles has increased. An automobile does not have a large amount of volume to physical space, and space planning of the seat arrangement greatly influences passenger comfort. The seat arrangement changes the visual environment of the passenger. Previously, the authors proposed a technique to evaluate comfort through the seat arrangement by using the passenger's space and vision. In this evaluation technique, vision is recognized as volume. A useful seat arrangement with a rotated seat utilizes the effect of vision for improving passenger comfort. In this paper, a sensory evaluation and a biomedical measurement are performed. Therefore, the effectiveness of a seat arrangement with rotated seats is shown to improve passenger comfort.
Cars are requested to obtain a wide room space and a compact package at the same time. Expression of depth through gradation of brightness is known well in general, and in this study, subjects were experimented whether car room could be shown larger when this method using a gradation tunnel pattern, was applied to the interior of a car. Following results were derived from the experiment, by sorting and analyzing subjects' comments and analyzing variances of numerical data, and it was clarified that the method is influential in the sense of depth. 1. The depth perception created by the gradation tunnel pattern is a few centimeters, more or less. 2. There are both cases when it seems dented and when it seems swollen. 3. Black centered pattern looks deeper than white centered pattern. 4. Stepping gradation pattern looks deeper than continuous gradation pattern. 5. How it is perceived varies among subjects, and roughly they could be divided into four groups. 6. What looks deeper is not necessarily preferable, and the application to door trim seems adequate.
A design methodology for both comfortable and accessible passenger rooms for public transport has been developed based on observation and modeling of seat-taking behaviors. The developed model consists of variables of visual environment of passenger rooms, whose parameters are identified through full-scale mockup experiments. The model enables quantitative comparisons between design alternatives of seat arrangements and door usages, thus this has been applied to propose seat arrangements for railway vehicles, light rail vehicles and a new unmanned energy-saving small urban transport system called “Eco-Ride” with small additional procedures for model extension.
The revealing power was proposed as an index to evaluate visibility in road lighting. However, applicability in tunnel lighting has not been studied. We evaluate the tunnel lighting visibility on the basis of the revealing power in this paper. Our simulation and field experiment, made clear the relationship between the brightness and overall uniformity of the road surface and revealing power. This result confirms tunnel lighting can reduce the road surface luminance while maintaining visibility and can also save energy.
In an attempt to prevent excessive increases or decreases in speed when driving motor vehicles, Central Nippon Expressway Company Limited (hereinafter referred to as “C-NEXCO”) is currently conducting research on controlling a driver's sense of speed, etc., by installing light-emitting devices on highway shoulders at regular intervals and by regulating their emission of light according to an arbitrary light-emitting pattern. Research results on the control of speed utilizing light-emitting devices have been accumulated. Regarding conventional research to urge drivers to regulate their traveling speed by drawing their attention or guiding their lines of sight to blinking or the turning on of light-emitting devices sequentially placed along potentially dangerous road areas, one issue of difficulty concerned responding to excessive traveling speed caused by becoming “acclimatized” to the speed and any excessive decrease in speed during sagging road section. In this paper, as an effort to control the sense of speed utilizing the perception of self-motion induced by visual sensation (hereinafter referred to as “vection”) and as a focus on taxis that move in response to the stimulus of light (hereinafter referred to as “phototaxis”), we would like to report on a basic examination conducted through a questionnaire experiment using CG simulation images and the actual effects thereof, as verified in experiments on actual roads conducted using an expressway under construction (based on the examination results).
The Japan Coast Guard (JCG) provides the tidal current information at Kurushima Kaikyo Strait for vessels which are passing the Strait according to the Maritime Traffic Safety Law. In March 2012, we unified the information provision methods to the Electric Sign. We have 6 Electric Signal Boards at 4 Signal Stations and we installed 4 LED Signal Boards at 2 Signal Stations. The result of visibility survey of the signal boards using LED Units shows good condition to provide the tidal current information for vessels at Kurushima Kaikyo Strait area.
This paper introduces a system of symbolized intersection and its effectiveness. In the system, each intersection has been named as one of alphabet, and the guide sign of an alphabet is placed at each intersection. The guide sign can be clearly distinguished by drivers and also it can be understandable from longer distance. Because of these properties, sudden deceleration or dull traveling is expected to be decreased and consequently safety/smoothness of the traffic is expected to be improved. Also, the guide signs are expected to bring more understandable route guidance. The guide signs named “Co Co Mark” are proposed and are actually used in Kochi city. The knowledge of the benefit acquired through the experiment on the actual road network is shown below.