Journal of Light
&
Visual Environment

Volume 26 Number 2, March 2002

CONTENTS

Papers

Papers Presented at 2002 Annual Conference of IEI-J, August 8-9

English Abstracts

Methods were investigated to improve the lamp characteristics of inductively coupled electrodeless metal halide lamps to make them practical. First, evaluating lamp efficacy by adjusting the lamp parameters showed that a lamp efficacy of 180 lm/W (Including coil loss: 151lm/W) white color could be attained. Second, the conditions generating free iodine and bulb deterioration, the main factors limiting the life of these lamps, were investigated. For long-life-type lamps, which had 130 lm/W of lamp efficacy, the lamp lumen level did not decrease during 21,000 hours of overload operation (corresponding to 58,000 hours of rated-load operation). These lamps thus have excellent lumen maintenance and life performance compared with conventional electrode metal halide lamps. Third, improving circuit reliability by decreasing the Q value of the resonant circuit was investigated for long-life-type lamps which had 145 lm/W of lamp efficacy. The relationship between the Q value and the lamp parameters was analyzed, and the Q value was decreased to 78% its value while maintaining the same lamp performance.

Recently, the T8-4ft. fluorescent lamp systems with high frequency (HF) electronic ballasts have been promoted as a strategic energy-saving product even into the outdoor lighting fields. In such a situation, the troublesome pinkish-colored cataphoresis phenomenon of these lamps is observed especially in the outdoor fields of winter seasons. The cataphoresis phenomenon of FLs is currently considered to occur only in the DC operation and hardly in the AC operation. Nevertheless, conventional HF electronic ballasts keep inherently the superimposed DC voltage component VDC, attributed mostly to the duty unbalance in the HF inverter circuit.This paper shows that the cataphoresis phenomenon of T8-4ft. fluorescent lamp systems with HF electronic ballasts is analyzed in relation to definitive parameters of the coldest tube wall temperature Tc and the superimposed DC voltage component VDC. This has clarified the critical cataphoresis phenomenon outbreak conditions, given by the equation VDC = 0.56 Tc-4.3. In addition, through the experiments on the lamp burning hours to the cataphoresis phenomenon outbreak, the ballast design requirement of VDC less than 2V is proposed as an actual suppression measure against the cataphoresis phenomenon.

A method is described for reducing the large error that often occurs in the measurement of three-dimensional (3D) objects using the photometric stereo method when there is a specular component in the reflection characteristics of the object's surface. First, the change in the luminance distribution caused by the component is estimated based on the correlation between the modeled distribution and a gray-level image of the object, created by numerical experiment. Next, the shape measurement of the hemisphere object was carried out. Numerical experiment of three dimensional measurement of a hemispherical object showed that the mean error of normal vector can be reduced by as much as 90%. This method is applicable to machine vision, automatic manufacturing, and other industrial processes.

Which lighting attributes determine the brightness of a room space? We considered the perceived strength of the light source and the perceived amount of light in the space as potential determinants. We examined the relations between the actual brightness of the space and these two perceptions. In the first experiment, subjects evaluated the strength of the light source and the amount of light in the space using reference matching method. The results were consistent among the subjects, indicating they judged each of the two lighting attributes by some common criteria. In the second experiment, the brightness of the space, the strength of the light source, and the amount of light in the space of a model box were evaluated using the magnitude estimation method under various illumination conditions. We found that the brightness of the space was closely correlated with the perceived amount of light but not with the perceived strength of the light source. These results should prove useful in constructing a model for quantitatively estimating the brightness of the apace.

Our study sought to establish a universal and comprehensive method for evaluating the visibility of a human face. This paper examines the peculiarity of a human face as a visual object and the prerequisites required for an evaluation method. Two experiments were carried out under various lighting conditions to subjectively evaluate the visibility of a human face seen through a lace curtain. These experiments showed that verbal expressions used to evaluate the whole human face were related to those used to evaluate each part of the face, and that the luminance contrast between the cheek and the eye was a visual factor corresponding to the visibility human face.

For a reflection type hologram such as Lippmann hologram, an incoherent light can be used to reconstruct the image. An artificial light emitted by electric lamps such as halogen lamps is frequently used for this purpose. Incoherent light is of great use for the deep or protruded image reconstruction. However, it has been considered that a good image was could not be obtained using commercial lamps with the narrow beam angles. This paper investigates other factors of lamps referring to the principle of holography.