Journal of Light & Visual Environment

CONTENTS

Papers

English Abstracts

The plasma density, electron temperature, and spectral line intensities from barium atoms and ions in the vicinity of the fluorescent lamp electrode in addition to the hot spot temperature have been measured as a function of the lamp operating frequency. The plasma density increased, while the hot spot temperature decreased, as the operating frequency was increased. This caused an increase in the spectral line intensities emitted from the barium atoms and ions at high operating frequencies, which might lead to a serious sputtering of the emitter material coated on the electrode. These phenomena can be well explained as follows. The high density plasma near the electrode produced during the cathode cycle can be sustained when the ambipolar diffusion time in the anode cycle is longer than the period of the operating frequency. In turn, the high density plasma around the electrode can effectively reduce the anode fall, so that the hot spot temperature is decreased. Thus, the cathode fall voltage develops under high operating frequency, and the ions are accelerated to enhance the sputtering of the emitter material during the cathode cycle. Consequently, the auxiliary electrode heating should reduce the amount of sputtering and extend the life of the fluorescent lamp.

Mercury-free Xe flat discharge lamps were developed for the use of lighting equipment. The lamps have a simple structure with insulated electrodes and operated with an ac pulse voltage. By adopting 1mm-wide electrodes, gas pressures of 10kPa or higher, and 50% duty pulse voltage drive, high luminance and high efficacy were achieved. Two types of mercury free Xe flat fluorescent lamps, a single discharge type and a multiple discharge type, were introduced. Luminance of 11,000cd/m2, luminous flux of 860 lm, and efficacy of 30 lm/W were attained with the 444mmX27mm single discharge type lamp. Luminous flux is sufficient for lighting, although the efficacy is half that of the commercially available Hg fluorescent lamp. A proto-type of a table lamp that utilized a 175mmX110mm multiple discharge type was also made. Luminous flux and efficacy were 850 lm and 21 lm/W, respectively. Illuminance at the position 38cm under the lamp was 1,700 lx, which is higher than that of a commercially available table lamp.

The size of the recognized visual space of illumination (RVSI) is a concept for expressing the perception of brightness of a space recognized by an observer. If he/she recognizes the space as being brightly illuminated, the size of RVSI is said to be large. The apparent lightness of an object placed in the space is determined relative to the size of the RVSI. The size is controlled by changing the illumination level of the space. It can also be controlled by changing the lightness of the interior of the space even if the illumination is kept constant. Then the apparent lightness of the object becomes lower with an interior having high lightness. Two miniature rooms in the depth direction from a subject, were illuminated at the same illuminance level, but the front room had walls, floors and furniture with lower lightness than the back room. It was expected that the RVSI of the front room would be smaller in size than that of the back room. The two rooms were separated by a partition frame projecting from the side walls. In this paper the effect of the projection size of the partition on the size change of RVSI at the boundary of the two rooms was investigated by measuring the apparent lightness of a test patch along the depth of the rooms for three different projection sizes. It was found that the effect of projection size was not significant and that the separation into two RVSIs was mainly achieved by interior lightness.

It is a well-known fact that the visual characteristics of humans are heavily affected by differential visual environments. This paper describes an experiment in which we examined how object colors look like in a dense fog. Seven male subjects with normal color vision contributed to the evaluation of their perception of object colors in the dense fog.The subjects were asked to match the colors of ten standard color cards, as perceived in the dense fog, with Munsell color sheets at hand.The results of our experiment made it clear that the apparent chroma and value tends to reduce with increased density of the fog in any of the color chips.We believe that these experimental results will come to provide useful basic data not merely in the fundamental research relating to the vision but in any such practical aspect as the countermeasures for traffic visual environments in a dense fog.

It is well known that color appearance depends on the visual environments. In this experiment, Apparent color and hue-shift in the small visual angles were investigated quantitatively employing the color-matching method. Four observers with normal color vision and visual acuity participated in this experiment. The results showed that Munsell Chroma decreased, on the other hand, Munsell value increased as the decrease of the visual angles. Namely, color perception shifted from chromatic color to achromatic color. It was also made clear that color appearance of yellowish and bluish especially changes in the small visual angles. We are confident that in the visual environments involving small visual angles, these results are useful both for the basic study and for the practical applications.

The perceived whiteness of a white object was investigated using psychological experiments. Six types of whitish light sources were used; their spectral distributions were varied by using four types of colored filters. The illuminance level was kept constant at 1000 lx. Paired comparison was used to construct the interval scale for the perceived whiteness. A new index was developed to evaluate the perceived whiteness under various illuminants. The index is proportional to the ratio between the chromatic and achromatic responses in the visual system. The chromatic response is based on opponent color theory. The index was highly correlated with the results of the experiments. It can thus be used to evaluate perceived whiteness under various illuminants and suggests that the chromatic response affects the perceived whiteness.

A new non-linear uniform colour space NC-IIIC is developed for colour specification. At the start, NC-IIC space is derived by applying non-linearity at the receptor level to linear colour space NC-I composed of linear transformations of tristimulus values X, Y and Z. Then, NC-IIIC space is constructed by further introducing non-linear and non-symmetric functions in Y-B and R-G opponent colour response mechanisms to NC-IIC space. For colours aligned on a plane of constant value in Munsell space, coefficients of the above non-linear response functions are optimized by computer numerical analyses to make hue circles shape as close as possible to uniform circles in the new space.
The uniformity of the space is significantly improved, and the average deviation between hue circles and uniform circles in the new space is reduced to about 1/10-1/20 of those in conventional L*a*b* and L*u*v* uniform colour spaces by applying appropriate non-linear opponent transformations. Hue, lightness and chroma can be represented independently as mutually orthogonal attributes with proper correspondences of hue with hue angle, lightness with metric lightness and chroma with metric chroma in the new colour space NC-IIIC.

In various interior spaces, specific trends are often discerned in combinations of the type of space and the method of lighting used. The type of space determines the type of lighting because of the relationship between characteristics of lighting methods and the ease of certain behaviors. This study examined the method of lighting preferred for interior behaviors. First, preferred lighting non-uniformity for behaviors was investigated using a questionnaire. Next, an experiment was carried out searching for the degree of lighting non-uniformity preferred for behaviors using a reduced scale model. The results of the questionnaire survey and the experiment were clearly similar, it was possible to quantitatively predict trends in the non-uniformity of interior lighting preferred for many other types of behavior not covered by this experiment.

A new digital illuminance-meter "MINILUX" with a special luminance-tubeadapter is developed by the University of Applied Sciences Berlin in cooperation with the Technical University of Zhejiang China for universal applications in lighting engineering.

Tri-color type fluorescent lamps have been improved in their performance by various research efforts since the introduction to the market. In recent years, however, small size lamps have appeared and phosphors with superior resistance have been required under the severe conditions of these lamps. When compared with green phosphor and red phosphor, (Sr,Ba,Ca)10(PO4)6Cl2:Eu blue phosphor(SCA) is particularly easy to deteriorate. To investigate the causes of deterioration of SCA, we made serial experiments by the demountable discharge lamp apparatus (DDLA) and the fabrication of actual fluorescent lamps. It is noticed that ion bombardment and mercury absorption are related to the deterioration of SCA lamps. Surface coating is found to be effective to decrease the influence of both.