Skin color has routinely been measured using a contact type colorimeter with a white light source such as a xenon lamp. However, it is difficult to reduce the weight of the apparatus due to its structure, and compression of the skin during colorimetry tended to induce changes in skin blood flow or morphological changes in the skin surface, resulting in measurement errors. Therefore, a colorimeter appropriate for colorimetry of the skin has been needed. We have developed a small light colorimeter (RGB sensor) using LEDs with the three primary colors (red, green and blue) as a light source. Comparison of colorimetric accuracy (color chips and actual skin color) between this sensor and the conventional contact type colorimeter revealed a high correlation (skin color chips: L*, R = 0.999; a*, R = 0.998; b*, R = 0.996. skin color L*, R = 0.921; a*, R = 0.892; and b*, R = 0.885). These results suggest that this small lightweight RGB sensor is as efficient and accurate as the conventional colorimeter, and appropriate for measuring skin color.
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.
The dependence of the cathode fall voltage (CFV) of hot-cathode low-pressure discharge, which depends on the cathode temperature, on the rare gases was measured for an operation frequency of 50kHz. The gases tested were Ne-Hg and Ar-Hg. The results showed that the CFV oscillated in Ar-Hg discharge, but not in Ne-Hg discharge. This difference can be explained by the behavior of the ions, produced by the collisions between the atoms and primary electrons emitted from the cathode. The primary electrons with sufficiently high energy to ionize the atoms change to Maxwellian electrons after the ionization. The ions thus produced diffuse to the cathode, which cause an ion current. The discharge current consists of the ion current and an electron current. If the ion current increases for some discharges, the electron current should decrease. This means the CFV decreases with an increasing ion current, because it decreases with a decreasing electron current (the Schottky Effect). The time for the ions to reach the cathode in Ar-Hg discharge was calculated to be shorter than in Ne-Hg discharge. This calculation also showed that the time for Ar-Hg discharge is nearly equal to the period of the CFV oscillation and that the time for Ne-Hg discharge is nearly equal to the time lag of the peak of the current to the peak of the CFV. Thus, the CFV under high-frequency operation depends on which rare gas is used because rare gas affects the ion current, which in turn affects the CFV.
Shadows cast over a work area can be a significant obstacle to work. Shadows are thus an important factor in designing comfortable work environments. The problems caused by shadows produced by a globe shadow caster combined with task ambient lighting in a room were modeled. The variations of the illuminance and the as a shadow factor were obtained and examined for various positions and sizes of an ambient light with a Lambertian surface with the position of the shadow caster taken as a parameter. The most suitable position for the ambient light was found to be the center of the ceiling, and the most suitable size for it was found to be 0.6 × 0.6-1.0 × 1.0 [m2].
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 kinds 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 estimate 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 estimate perceived whiteness under various illuminants and suggests that the chromatic response affects the perceived whiteness.
An excellent method based upon Mean Sky was developed by H. Nakamura et al. for predicting daylight illuminance in interiors. Numerical tables are given for the application for Japan. However, calculations using the numerical tables are not easy in practice. The goal of this research work is to develop a practical method of computer-aided daylighting calculation. For that purpose, the numerical tables are modified into mathematical equations. This paper presents the detailed procedure for converting the table on Mean Sky in Japan as the first step of this research work. The conversion was done by performing regression analyses repeatedly. The final equation is proposed as a function of the azimuth and altitude of the sky element. The average difference between the values in the original table and those calculated by the equation was 0.970% and with a standard deviation of 0.748%.
We can perceive small color differences, and we can also perceive color as a group of many different colors (categorical color perception). Visual performances based on small color differences are known to be better in the central visual field than in the periphery. We have clarified the characteristics of categorical color perception in the peripheral visual field. Observers were shown color chips of the OSA Uniform Color Scales set in the central or the peripheral visual field. The chip, which subtended 4deg, was presented at the fovea (Odeg), eccentricities of 30, 50, and 60 deg in the nasal visual field and of 30, 50, 70, 80, and 90 deg in the temporal visual field. A large gray surrounding field was made with a hemisphere and illuminated at a moderate intensity of D65 lights (yielding 2000 scotopic td) to suppress rod activity. The observers reported color appearance of the stimulus with one of the eleven basic color terms. The distributions of the color categories on the xy chromaticity diagram varied little between stimulus locations from 30 deg to the nasal and 70 deg to the temporal visual field. The results of eccentricities greater than nasal 50 deg and temporal 80 deg were remarkable different from those in the locations closer to the fovea. Our results suggest that categorical color perception in the central visual field is maintained across a wide area of the peripheral visual field.