J. of IEIJ Vol.86, No.2

The Abstracts of the Papers
J.Illum. Engng. Inst. Jpn. Vol. 86, 2002

Characteristics of Inductively Coupled Electrodeless Discharge Lamps with Magnetic Core
Yoshio WATANABE and Ken OHTA

 The characteristics of inductively coupled electrodeless discharge lamps using a ferrite core are investigated. The discharge tube has a hollow cylinder shape, and a ferrite core with an excitation coil is inserted into the hollow. A voltage is applied across the coil, and light emission is measured at 100 - 200 kHz. The voltage per turn of the coil is constant at about 7V. The luminous efficacy defined by the input power increases with the number of turns and is independent of operating frequency.
 The characteristics of the inductively coupled electrodeless discharge lamps are analyzed using the equivalent circuit. The luminous efficacy defined by the discharge wattage is independent of the number of turns. The core loss, which is mostly due to eddy current loss, is nearly constant when discharge takes place due to the constant discharge voltage characteristics, whereas the joule loss in the winding coil decreases with an increasing number of turns. Thus, the efficacy defined by the input power increases with the number of turns of the winding coil.

KEYWORDS : electrodeless discharge lamp, ferrite core, luminous efficacy

Relation between Chromatic Strength and Perceived Whiteness
Ichiro KATAYAMA, Kazuyoshi MASUMI and Tsutomu AOKI

 Using psychological experiments, we investigated the perceived whiteness of a white object under 30 types of illuminants. We used the index we developed in an initial study[J. Illum. Inst. Jpn. Vol.83 No.11(1999)] and modified in a subsequent study[J. Illum. Inst. Jpn. Vol.85 No.5(2001)]to evaluate the perceived whiteness. The index is proportional to the total chromatic strength of the spectral stimulus at a constant luminance level; it correlated highly with the experimental results, indicating that it can be used to effectively evaluate the perceived whiteness of a white object under various illuminants.
  Considering the ability of a spectral stimulus to induce brightness and chromatic perception, we investigated the cause of whiteness perception. We found that whiteness perception, the Helmholtz-Kohlrausch effect, the discrimination threshold level of colorimetric purity, and the G0 function studied by Evans are all caused by a basically common color perception mechanism and that they can be explained uniformly by using chromatic strength.

KEYWORDS : perceived whiteness, chromatic strength, brightness perception, Helmholtz-Kohlrausch effect, purity discrimination, G0 function

Visibility of a Visual Display due to Variation in Luminance while Driving
Mitsuyuki KAWAKAMI, Shuichi MATSUMOTO and Wakako KANEKO

 This research examines the ease of reading text on a car navigation screen as a visual display when the luminance of the driver's eye-fixation point differs from that of the screen while driving. To conduct this research, an experiment was performed to determine how such variation in luminance affects the time taken for a driver to read text displayed on a car navigation screen during driving operations. Evaluation indexes in this experiment were locus of eye-fixation point during movement of line of sight, duration of stationary viewpoint, and time taken to read text. Results of this experiment revealed the following. (1) Reading time for a screen luminance of 100cd/m² was short under nighttime luminance conditions of 2.5cd/m² exhibiting a difference of about 0.314s compared to 500cd/m². (2) Reading time for a driving environment of 500cd/m² with screen luminance lower at 25cd/m² was short exhibiting a difference of about 0.13s. (3) Reading time shortens as the ratio of monitor luminance to luminance while driving increases.

KEYWORDS : luminance, visual display, reading time

On Estimation of the Luminance Distribution by the Diffuse Reflection Component of the Object Surface and Shape Measurement - Analysis by the Numerical Experiment -
Naotaka IKEMOTO and Minoru ISOMURA

 A method is described for estimating three-dimensional
 (3 - D) shapes from two-dimensional (2 - D) shading information in gray-level images that uses the diffuse reflection components in a luminance distribution with diffuse and specular reflection components. It overcomes the problem of highlights caused by the specular reflection components that occurs when multiple fixed light sources are used, which is a drawback to the “photometric stereo” method proposed by Woodham. First, the bidirectional reflectance distribution function is estimated for the detected area of a gray-level image with highlights. Then, the luminance distribution caused by the diffuse reflection components in the detected area is estimated based on the luminance distribution in a gray-level image without highlights. Numerical shape-measurement experiments using mixed diffuse-specular objects with different characteristic reflectances and shapes showed that the proposed method can accurately measure the 3 - D shape of mixed diffuse-specular objects.

KEYWORDS : bidirectional reflectance distribution function, reflection characteristic, photometric stereo, highlights, shape measurement, mixed diffuse-specular objects

A Study of the Light Source Device Composed of Blue LEDs and YAG Phosphorby Using Optical Simulation
Kenichi YAMADA, Yasuo IMAI and Kenichi ISHII

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

KEYWORDS : LED, YAG phosphor, light source, optical simulation, reflection-type

A Relation between Visibility of Color and Working Efficiency
Mitsuyuki KAWAKAMI and Tohru SHIBAYAMA

 We investigated how color visibility affects work efficiency. In particular, we experimentally invesligated how differences in bue affect the motion of touching a control button. The evaluation indexes were the time it took to respond to a stimulus, the time it took to move the hand to the button, and the frequency of motion confusion. We found that different hues affect work efficiency differently. With warm colors, if the background color is achromatic and the brightness is low, yellow is highly visible, resulting in high work efficiency. With cool colors, if the background color is achromatic and the brightness is high, blue or purple results in high work efficiency.

KEYWORDS : hue, working efficiency, response time, motion time, confused frequency

Study on Color Design for Computer Display by Visual Search
Kazuhiro SASSA, Mamoru TAKAMATSU,Yoshio NAKASHIMA and Santaro NAKAJIMA

KEYWORDS : color design,computer display,visual search