Journal of Light
&
Visual Environment

Volume 27 Number 2, August 2003

CONTENTS

Papers

Phenomenon of End of Life in a Fluorescent Lamp and By-Investigation of Alkali Metal
Adsorption System
M. MYOJO and O. FUKUMASA

English Abstracts

  The mechanism that causes the end of lamp life (EOLL) phenomenon in a fluorescent lamp should be clarified to achieve an effective measure for that. The EOLL phenomenon, including the tungsten sputtering from an electrode, is investigated. We observed the electron emission from a lead in the vicinity of the stem glass. The electron emission causes the intermittent pulse discharge that heats up the stem glass. The concentration of lamp current directly into one of leads is another factor to heat up a small glass portion around the lead. The comparison of the stem glass resistance and the glow discharge impedance between leads after the filament disconnection indicates whether or not the stem glass will begin to soften. It was shown that the heating of a small glass portion around the lead was a dominant factor that resulted in the final stage of EOLL, that is, a substantial overheating of a lamp end portion.
 The way of operation for testing the life-ended fluorescent lamps is expected to contribute to the further understanding of the alkali metal adsorbate on metal surface.

KEYWORDS: fluorescent lamp, end of life, overheating, emissive coating, depletion, alkali metal adsorption

 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.

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

 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.

KEYWORDS: lighting fluctuation, lighting control, fluctuation in illuminance, office lighting

 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 0.01lx 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.

KEYWORDS: peripheral vision, chromatic component, hue component, object color, illuminance level

 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.

KEYWORDS: control, illuminance change, office lighting, satisfaction level, interview, evaluation

 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.

KEYWORDS: modeling, CCD camera, security