Showing papers in "Journal of Light & Visual Environment in 2000"

A Study on the Practical Use of a Task and Ambient Lighting System in an Office

Abstract: The possibility of the practical use as an office lighting system, which make the total illuminance of 400lx and Task and Ambient illuminance ratio of 1.0 on the working desk, by using Task and Ambient Lighting system was reported on the last year research. On this year research, the following aspects were indicated based on the analysis of the psychological queries after two weeks actual work in the specific illuminance level and Task and Ambient illuminance ratio. The illuminance level of 200lx on a working desk cause some psychological problem as room and desk area ‘darkness’ and illuminance level ‘unevenness’. These problems were improved when the illuminance level of 300lx was applied. And this analysis suggested that the Task and Ambient illuminance ratio shall be around 1.0. An approximately 20% saving energy can be achieved under this lighting system condition compared with the general office lighting system.

An Electronic Ballast Using Modified Two-Switch Boost Converter.

Abstract: This paper proposes a modified two-switch boost converter with high power factor, and makes a report concerning the application of it to electronic ballast. First, the behavior of the boost converter with two switching devices is analyzed and experimental results will be shown. The experimental results show that the circuit can decrease the harmonic distortion of the input current like a former boost converter. But the problematic points possessed by the circuit are to be scrutinized. Next, a modified boost converter circuit that can improve the problem is proposed. The proposed circuit has both function of boost chopper and charge pump. The experimental results show that the circuit can improve the power factor. Lastly, it is shown that these two switching devices can be used not only as active switches of the modified boost converter but also as active switches of a half-bridge type inverter for fluorescent lamp. As a result, it is revealed that the harmonic distortion of the input current obtained by the proposed electronic ballast sufficiently satisfies the maximum limit of IEC 1000-3-2 class C. And the electronic ballast realized the high power factor of 0.99.

A New Daylight Glare Evaluation Method

Abstract: A proper glare prediction method is needed to promote visual comfort at workplaces. Only a few formulae have been proposed for discomfort glare of daylight origin, and they are inadequate in real daylight situations. No standard monitoring procedure is available for daylight glare evaluation on a comparative basis. This paper introduces an improved glare evaluation method consisting of a standard monitoring protocol and advanced formulae. The method has been tested against the existing glare evaluation system of Chauvel on different types of window size using Radiance, a lighting simulation program. Given reliable results, the DGIN procedure was coded into a small program and incorporated with Radiance to compute daylight glare indices. The method was developed with the hope that architects and lighting designers would adopt it as an easy and reliable method for evaluating discomfort glare from daylight. The future work, which is an ongoing research, is to create the use of scientific-knowledge computational tools in the later stages of design in an effort to provide optimum choices of daylighting design with respect to light level and glare using the new glare algorithm.

The Use of Multiple Reflection Method for Calculation of Luminous Flux in Interiors.

Abstract: The paper presents a multiple reflection method for calculation of luminous flux in interiors. The method of boundary integrals has been applied, as well as a procedure of formulating a system of linear equations describing discrete values of overall luminous flux at particular surface elements of considered interior has been presented. Some calculation examples are reported, as well as discussion of obtained results.

The Self-Ballasted Compact Fluorescent Lamp of an "A60" Bulb Shape

Abstract: Self-ballasted compact fluorescent lamps (CFLs) have been developed and improved in these twenty years. In Japan, the CFLs that have diffusive glass globes to replace incandescent lamps have been developed, but their sizes were too large to fit in the luminares of incandescent bulbs. Thus, we have developed the self-ballasted CFL of an "A60" bulb shape, which has the maximum diameter of φ60 mm and the length of 123 mm. This lamp could be substituted for a 60 W incandescent lamp. In order to realize this lamp size, we optimized the discharge tube diameter, filling gas type and pressure, the shape and making-process of the discharge tube. After all, the triple-"U" connected tube is selected, which has a decisive advantage against a multi-folded tube on the luminous maintenance during life, but also has a disadvantage on the luminous run-up characteristics. We investigated the behaviors of mercury, especially the mercury diffusion phenomenon released from the auxiliary amalgam-flags after ignition by both experiments and calculation. The luminous run-up characteristic has been much improved.

VUV Radiation of Afterglow Generated by Pulsed Discharge of Xenon

Abstract: The characteristics of xenon-neon discharge fluorescent lamps with inner electrodes and of xenon discharge lamps with external electrodes are described in this paper. All these lamps were operated at pulsed discharge. In the case of inner electrode type, when the partial pressure of neon is high, the ignition voltage is low because of the Penning effect. Then, the high mixing ratio of neon is desirable for the lower ignition voltage. However, the luminance of phosphor increases as the mixing ratio of xenon increases. Therefore, in order to obtain high luminance, xenon should be filled at high mixing ratio. In both cases, that is, inner electrode type and external electrode type, as the pressure of xenon increases, the afterglow peak of phosphor emission increases. These increases seem to be caused by the VUV radiation of xenon excimers. The emission of light from phosphor shows that xenon excimers are generated effectively by pulsed discharge of high pressure xenon, because they are generated by three-body collision at the low electron temperature Te during the non-discharge period.

Senescent Changes in Color Discrimination and Color Appearance

Abstract: Age-related anatomical and physiological changes in the human visual system have been reported such as an increase in the density of the lens, a reduction of pupil size and loss of retinal ganglion cells. Although the retinal stimulus and neural signals are strongly affected by such age-related changes, color appearance is stable throughout the life-span because of parallel losses of cone sensitivities and other compensation mechanisms related to color constancy. On the other hand, there is a loss of sensitivity in color discrimination due, in part, to the reduction of retinal illuminance. The results of recent experimental studies by the author and colleagues indicate that this loss in discrimination is not only caused by the reduction of retinal illuminance, but also by a decrease in the signal-to-noise (S/N) ratio in neural pathways processing signals from S-cones and antagonistic signals from L- and M-cones. This change can be considered as a sort of a trade-off between maintaining a constant signal level from the cones through the life-span and decreasing the signal-to-noise ratio in the human visual system. These results suggest some possible methods for making safer and more comfortable visual environments for the elderly.

Preheating Characteristics of a Fluorescent Lamp Cathode (II)

Abstract: High-frequency fluorescent lamp operation requires proper cathode preheating by electronic ballasts incorporating a preheating function. This paper examines minimum thermionic emission curves for three different ways of measuring emission times. One is based on a lamp ignition test, another on the ratio of hot to cold coil resistance (Rh/Rc), and the third on the lamp voltage monitoring. The observation that the emission time measured by the lamp ignition method tends to be shorter than that measured by the lamp voltage monitoring method in a short preheat time may be understood in terms of the relaxation of the limited thermal conductivity of the emissive material due to the initial flow of the discharge current. We do not believe that the shorter emission time measured by the lamp ignition method causes premature thermionic emission. On the other hand, when the duration of the heterogeneous heating in a cathode is negligible, then the Rh/Rc method may be used as well. This paper points out that the average resistance of a standardized cathode over the period up to the emission time should be regarded as a substitution resistor. Furthermore, a maximum curve similar to the minimum preheating requirement curve, being examined to replace the maximum preheating broken lines for the present requirement in the IEC, is helpful for determining a new coming maximum required energy line. In the last part of this paper, an approach to the standardization by a preheating energy line together with a suitable value for the substitution resistor is supported.

Fundamental Study of Shadow Characteristics under Task Ambient Lighting

Abstract: Shadow is something we experience in our daily lives and a significant obstacle to our work So shadow has been considered one of the important factors in lighting design In this paper, the illuminance distributions on a desk as the working plane when Task Ambient Lighting, which is one type of office lighting systems, and a globe as a shadow caster are set up in a model room containing fixtures are obtained by the Monte Carlo method and the characteristics of the shadow are examined First, in order to carry out the illuminance calculation by the Monte Carlo method in the case of a light source with a non-uniform diffuse distribution, the relationship between the cumulative luminous flux and uniform random numbers was found by the use of division mensuration Next, some experiments were made under the same conditions as the calculations Comparing the experimental results with the calculated results, difference between them, confirms that the above method is suitable Then, we obtained and examined the shadow characteristics on the surface of the desk when the position of the shadow caster was changed As a result, we found that Task Ambient Light makes a weaker shadow than one of Task light or Ambient light, and variations in the shadow area by Task Ambient Light are similar to those by Task light

Study on Affluent Lighting in a Japanese Living Room. Meanings of Affluent Lighting and Elements Concerned.

Abstract: The purpose of this study is to clearly define the meaning of affluent lighting in a living room and together with its concerned elements. Two psychological experiments, one using the evaluation grid method and other using the semantic differential method, were carried out using photographs of living rooms. (1) 24 meanings and 41 elements emerged from the results of experiments using evaluation grid method. Relationships among the 24 meanings were plotted in a figure using MDS. The 41 elements were classified into six groups. (2) The meanings of affluent lighting were explained by feelings of comfort, brightness, and variety from the results of experiments using the semantic differential method. The important elements were plural luminaries and brightness. The results show that affluent lighting can suit various situation in a living room.

Illuminance Calculation Using Monte Carlo Method

Abstract: The Monte Carlo method, which has recently been widely used to predict the illuminance distribution of a room arranged in a complicated way with furniture, is an easier algorithm than others and is suited to simulating the various states of lighting in a room. The accuracy of the illuminance distribution calculation is affected by the number of particles that substitute for the luminous flux of the light source and by the number of elements of the room surfaces. Therefore, we investigated the optimal number of the particles and elements considering the CPU time and error rate of the illuminance calculation when a shadow caster assumed to be a worker's head was set at an arbitrary position in a rectangular parallel-piped model room. A new method, which uses the incident particles on the surrounding elements of the calculation point, was developed to decrease the CPU time and calculation error. We examined various reflectances of the room surfaces, positions and diameters of the shadow caster. As a result, using only 1/10 the CPU time of previous methods, we found that the optimal number of particles is five million and the optimal number of elements each surface of a room is 40×40 to 60×60.

Annealing Behavior of Emission Bands Induced by Neutron Irradiation in Silica Glass

Abstract: The continuously emitting 4.2 eV, 3.2 eV and 1.9 eV photoluminescence (PL) bands were measured for as-manufactured and neutron-irradiated silica glasses. In the as-manufactured sample, the intensity of the 4.2 eV decreased with increasing temperature from 77 K to 550 K. The 3.2 eV band observed at room temperature was too weak to be observed at 77 K, and the intensity increased till 80 °C, and decreased above 110 °C. In the neutron irradiated sample, the intensity of the 4.2 eV PL band increased, and the peak position shifted to 4.37 eV. After annealing to 600 °C, the intensity at room temperature became weaker than the original, and the peak position continued to shift to higher energy side. On the other hand, the intensity of the 3.2 eV PL band decreased drastically and almost disappeared, and any shifts of the peak position were not observed. After annealing to 700 °C intensity at room temperature began to increase, and the peak position kept the original position. The 1.9 eV PL band was observed after neutron irradiation, and depended on the OH content in the as-received samples. After annealing, the intensity of the 1.9 eV band increased gradually up to 450 °C and then decreased and almost disappeared at 700 °C.