Showing papers in "Journal of Light & Visual Environment in 2003"

Optical Simulation of Light Source Devices Composed of Blue LEDs and YAG Phosphor

Abstract: The optical structures and luminous properties of light source devices composed of blue LEDs and YAG phosphor were examined using optical simulation. Results showed that the reflection-type light source device had a high luminous flux over 1.5 times greater than the transmission-type light source device. This suggests that using light reflected from the phosphor is an effective way of obtaining high output from light sources composed of LEDs and phosphor.

Present Status of White LED Lighting Technologies in Japan

Abstract: “The light for the 21st century” Japanese national (Akari) project, which is based on the high-efficient white light-emitting diode (LED) lighting technologies using near ultraviolet (UV) LED and phosphor system, has been started at 1998. The near UV white LED system linked with semiconductor technologies on GaN LED and ZnS phosphors for general lighting applications has for the first time been proposed in the project. The outline and purpose of this project are briefly introduced. In particular, we have demonstrated high-efficient nUV LED having external quantum efficiencies more than 43 % around an emission wavelength of 400 nm. Basic illumination properties of the high luminous efficacy (>40 lm/W) and the high general color rendering index (Ra>90) white LED sources are described. The near UV white LED technologies in conjunction with phosphor blends can offer superior color uniformity, high Ra and the excellent light quality for many lighting applications.

Perception of Lighting Fluctuation in Office Lighting Environment

Abstract: The non-periodic fluctuation of artificial lighting in offices was investigated to clarify the threshold at which the fluctuation is perceived. The experiments showed that fluctuation ratio of 0.92-1.06, i.e. 7% of the fluctuation, is not perceived when the observers tried to be conscious of the fluctuation. On the other hand, under the condition of being unconscious of the fluctuation because of assigned visual tasks, the threshold has a broader range (0.8-1.3) and the value rises with the fluctuation period. It is important to dim artificial lighting without causing discomfort to office workers, and the results of this study can be used to better control, fluctuation in office lighting.

High Output Power Near-Ultraviolet and Violet Light-Emitting Diodes Fabricated on Patterned Sapphire Substrates Using Metalorganic Vapor Phase Epitaxy

Abstract: Near-Ultraviolet (NUV) and violet light-emitting diodes (LEDs) with an InGaN multi-quantum-well (MQW) structure were fabricated on patterned-sapphire substrate (PSS) using a single growth process of metal-organic vapor phase epitaxy (MOVPE). The PSS with parallel grooves along the GaN direction or the GaN direction was fabricated by standard photolithography and subsequent reactive ion etching (RIE). In this study, the PSS with parallel grooves along the GaN direction was used. The GaN layer grown by lateral epitaxy on a patterned substrate (LEPS) had dislocation density of 1.5×108 cm-2. The LEPS-NUV (or violet)-LED chips were mounted on the Si bases in a flip-chip bonding arrangement. When the LEPS-NUV-LED (the emission peak wavelength λp: 382 nm) was operated at forward-bias current of 20 mA at room temperature, the output power (Ρo) and the external quantum efficiency (ηe) were 15.6 mW and 24%, respectively. When the LEPS-violet-LED (λp: 405 nm) was operated at forward-bias current of 20 mA at room temperature, the output power and the external-quantum efficiency were 26.3 mW and 43%, respectively. The PSS is very effective in reducing the dislocation density and increasing the extraction efficiency in the LEDs because of the scattering of the emission light at the patterned GaN/sapphire interface.

A New Criterion for Road Lighting: Average Visibility Level Uniformity

Abstract: This study aims to evaluate the effect of the lower uniformity ratios on the visual conditions while keeping adequate average visibility level on the road surface. A computer program has been developed to determine necessary criteria for calculations of the road lighting based on visibility level. Five different arrangements such as left single-sided, opposite, staggered, twin-bracket central and combined twin-bracket central & opposite are examined. The results obtained from the calculations for each arrangement by using one typical cut-off, semi cut-off and non cut-off luminaires are classified in two groups as sufficient and insufficient uniformity. It is seen that there are some invisible area even recommended average visibility levels and luminance uniformity ratios are obtained. Because the visibility levels on the grid points may take values different than the average visibility level of the road, a different lighting criterion is necessary to reduce the excessive variation of them. To prevent all possible negative visual conditions, a new road lighting criterion is defined and called as “Average Visibility Level Uniformity”.

Causes of Individual Differences on Brightness/Luminance (B/L) Ratios

Abstract: On individual variation of Brightness/Luminance (B/L)-ratio effect, the causes of its individual differences are studied. Based on the present study, the following conclusions are confirmed. 1) The individual differences on B/L-ratio effect are caused by the differences in attitude between subjects on equi-brightness judgement. 2) For the present, we must satisfy with a theoretical prediction of the average experimental B/L ratios derived by observations using a number of subjects.

Equivalent Luminance Contrast Representing the Relationship between Color Difference and Readability of Chromatic Documents

Abstract: The purpose of this study is to obtain data based on the readability of chromatic documents for use in visual environment design. That data would seem to be the same as the existing data based on the readability of achromatic documents. Experiments are undertaken in order to clarify the influence of color on readability. The results show that the same CIELAB color difference does not have the same influence on readability. In addition, it is thought that the equivalent luminance contrast is invariable irrespective of the size of a letter and is instead determined by the combination of the colors of the letters and the background. It is suggested that the readability of chromatic documents can be estimated by using the equivalent luminance contrast and the existing relationship between the visual factors and readability of achromatic documents.

All Sky Model as a Standard Sky Luminance Distribution : Part 2 A Numerical Expression of Sky Luminance Distributions for All Sky Conditions

Abstract: The aim of this research work is to establish a standard sky model for designing excellent daylighting schemes that cover all sky conditions from clear sky to overcast sky. In the previous paper (Part 1)1), the “normalized global illuminance” was defined as a function of the measured global illuminance and the solar altitude for estimating the sky luminance distribution. In this paper (Part 2), the “Relative All Sky Model” is introduced. It offers formulas to show the relative sky luminance distribution as a function of the normalized global illuminance. The equation of the zenith luminance concerning the Relative All Sky Model is also a function of the normalized global illuminance. It is called the “All Sky Zenith Luminance”. An absolute standard sky luminance distribution model called the “All Sky Model” is introduced that is a multiplication of the Relative All Sky Model and the All Sky Zenith Luminance. The All Sky Model can be calculated from the normalized global illuminance, i.e., from the measured global illuminance and the solar altitude or from the measured global illuminance, the horizontal diffuse illuminance, and the solar altitude. The global illuminance and horizontal diffuse illuminance are easily obtained from even the simplest daylight measurements. The All Sky Model can produce an excellent standard sky for daylighting design for any place where an advanced daylight environment is needed.

Short Wavelength LED Based on III-V Nitride and its Applications

Abstract: The short wavelength LED (“TG Purple”) based on III-V nitride semiconductors is established in addition to blue and green ones. This short wavelength LED is realized by adjusting indium chemical content of the well layer. Light output power of “TG Purple” is high and FWHM (full width at half maximum) is narrow. “TG Purple” is applied to light source of the white LED. Combination of “TG Purple” and various phosphors can generate white light with high luminous intensity and good color rendering. “TG Purple” is also applied to light source of air-purifier. This air-purifier is being offered as standard equipment in luxury automotives and several applications of this system are widely utilized in room air conditioners and refrigerators.

Novel Electronic Ballast for Automotive HID Lamps

Abstract: Simplifying the composition of the automotive HID lamp electronic ballast has been considered This paper describes the novel electronic ballast that is composed of a DC/DC converter, a capacitor connected to a lamp in series, a switch (S3) connected to the capacitor in parallel, a switch (S2) placed between the output terminals of the DC/DC converter and also connected in parallel to the lamp and the capacitor in series, and an igniter All MOSFETs (S1 in the DC/DC converter, S2 and S3) in the ballast are operated on the common voltage position (GND) of the circuit The DC/DC converter is operated intermittently and the operation of S2 synchronizes with the operation of it to supply the lamp with an alternate square wave voltage Operating an automotive HID lamp succeeded using the novel ballast and by setting some issues below 1) The occurrence of the power loss when S2 is turned on 2) The occurrence of extinction of gas discharge This paper describes how the loss can be decreased if a part of the energy stored in the output capacitor of the DC/DC conveter is used to operate the lamp before S2 is turned on It also describes how an inductor and a capacitor were added to the proposed electronic ballast to raise the lamp voltage in order to prevent the current from disappearing

Color Appearance of Object Colors in Peripheral Vision at Various Illuminance Levels

Abstract: The color appearance in peripheral vision was studied for chromatic object colors over a wide illuminance range from photopic to scotopic vision. Swedish NCS color samples with the existing maximum chromaticness at each of eight different hues were used for color stimuli in the experiment. The size of the stimulus was set at 2° of the visual field and the background was N2.5. The stimuli were presented horizontal and vertical meridians, and meridians inclined at angles of 45°. The illuminance level was set at six levels in the range from 0.01 lx to 1000lx. The evaluation method was to measure the chromatic, the white, and the black components, and the hue component of the stimuli. As a result, the chromatic component was found decreased with the increasing eccentricity, and the hues shifted toward yellow in the case of stimuli containing a yellow component and toward blue in the case of stimuli containing a blue component, when the illuminance level was decreased in the peripheral vision.

Effect of Personal Adjustment of Brightness on the Satisfaction Level of Office Lighting

Abstract: To clarify the importance of personal adjustments on office lighting, 17 general office workers and 38 experts in the lighting industry are interviewed. Experiments are conducted to quantify the effect of the subjects' capability to change the illuminance on their satisfaction level, and to distinguish the effect of “control” from the effect of illuminance change itself. It is shown through the interviews that although the awareness on the importance of adjustment is not prevalent, both general office workers and lighting designers regard lighting adjustment as a key factor. Through the experiments, it is observed that evaluations on the lighting environment vary greatly depending on whether or not the subjects are capable of adjusting the lighting level, while effects of both “control” and illuminance change are small.

On Deviations between Observed and Theoretically Estimated Values on Additivity-Law Failures

Abstract: The authors have reported in the previous studies that the average observed results are about a half of the corresponding predictions on the experiments with large additivity-law failures. One of the reasons of the deviations is studied and clarified by using the original observed data on additivity-law failures in the Nakano experiment. The conclusion from the observations and their analyses clarified that it was essentially difficult to have a good agreement between the average observed results and the corresponding theoretical predictions in the experiments with large additivity-law failures. This is caused by a kind of unavoidable psychological pressure existing in subjects participated in the experiments. We should be satisfied with the agreement in trend between them.

Study on Variations in the Visibility of Building Façades When Lit with Floodlights —Comparative Analysis of Direct Observation and Photographic Slides—

Abstract: This study focuses on the visual characteristics of buildings illuminated with floodlights, primarily investigating how the visibility of building facades varies according to the distance from an observer. The authors also attempt to compare the visibility of building facades between direct observation and photographic slides. The changes in the appearance of a building facade when illuminated with floodlights can be gauged according to the two stages of “perception” and “recognition.” There is also a typical gap between the visual recognition distances for direct observation and for slide viewing. Generally the visual recognition distance is longer for direct observation that for slide viewing. This is shown by the close correlation between the two types of observation for visual recognition distance for all of the buildings studied.

Effects of Auditory Tasks on Functional Visual Field against Dynamic Background

Abstract: The functional visual field (FVF) of target localization against a dynamic background simulating highway driving was precisely measured under four different auditory task conditions to investigate whether conversing on a mobile phone affects a driver’s FVF. The FVF is the visual field in which a person can achieve some kind of visual task, such as target detection or localization. The task conditions were no auditory information, listening to BGM, listening to a simple conversation and understanding it, and listening to a simple question and answering it orally. Individual differences were found in the size of the FVF and the effect of the tasks. The FVF area of the largest subject was twice that of the smallest subject under the same condition. Shrinkage of the FVF was found under the oral answer condition for the two subjects who had never used a mobile phone while driving, while no significant change under any condition was found for the subject who made a long drive every day and was used to talking on a mobile phone while driving. This suggests that conversation can reduce a drivers’ attention and shrink the FVF of some drivers.

On the Illuminance Distribution by Parabolic Reflector Type Irradiator

Abstract: Ultraviolet curing systems are used in various fields of industry. Two types of irradiators are commonly used in these curing systems: the parabolic reflector type and the ellipsoidal reflector type. Although the parabolic reflector irradiator is necessarily even, the illuminance distribution does not become even. This study proposes an irradiated plane illuminance calculation method for the parabolic reflector type irradiator. The validity of the calculation method was verified experimentally. In addition, it was clarified that the irradiated plane’s illuminance distribution can be made even by varying the reflectance characteristics of sections of the parabolic reflector.

Study on Modeling Effect of the Human Face on Monitoring Images

Abstract: Television images become to be used for various fields as security observation in addition to broadcasting. It will be useful to install a camera system for security in order to obtain “restraint of a crime” and “criminal information”. In particular, it is demanded to obtain “face discrimination” as criminal information. However, on an outdoor situation in the nighttimes there are many difficulties to obtain the “face discrimination” images by CCD camera. It is important how to establish lighting conditions to obtain video-monitored images. The lighting conditions are prepared by diversely modelled visual targets based on Cuttle's modelling evaluation experiments as reference and evaluating the level of “face discrimination” on the monitor. We discussed descriptive method for modelling effect using the illuminance as parameter.