The visual information available to us decreases selectively in hightemporal and highspatial frequency domains as viewing conditions change for the worse. Visual displays must therefore be legible in lowvisualacuity conditions and under conditions of short exposure. We ran three psychophysical experiments to evaluate legibility under these conditions, and have come up with several guidelines for display legibility. We measured the minimum visual acuity needed to discriminate letters with the lowpass-filtering method and the multi frame detection task. The first experiment showed the crucial effect of letter size on legibility. The results of the second experiment suggested that the optimal line width may be determined by a critical band of spatial frequency describing the letter shape and the power of a low-spatial frequency. The third experiment showed that background luminance had a significant effect on the discrimination of low-contrast letters. In other words, letter contrast must be about 0.9 in order to avoid the effect of background luminance.
Recognizing letters embedded in other letters is difficult. Framing (boxing) a symbol is thought to make it more conspicuous or easier to distinguish from the background. However, the frame may actually affect the legibility of the symbol adversely. This study evaluates the effects of spatial arrangement and framing on display legibility. One general characteristic of vision is that surrounding objects affect the perception of a central object. This is known as the crowding effect and is a type of spatial-frequency masking effect. We measured the minimum visual acuity required to distinguish crowded symbols by using the low-pass filtering method and the multi-frame detection task. The results showed that a framed symbol is less legible than an isolated symbol, and that the crowding effect is a function of distance between the symbol and a mask, and of contrast of the mask. The spatial spread of the effect was evaluated quantitatively.
Color differences in the CIE 1976 L*a*b*color space were scaled by measuring the critical area of detection with a colored patch on a white background. Several colors were selected to all have the same chromatic contrast with the white background but differ from one another in hue. The legibility of numerals painted with the selected colors were evaluated under Gaussian luminance noises. We found that red and green numerals were more legible than yellow and blue ones, despite the equalized chromatic contrast. The results are explained by differences in spatio-temporal resolution limits, which were estimated from the cutoff frequencies of chromaticcontrast sensitivity functions measured for different hues. The following properties of color vision must be kept in mind for coloring a legible display:(1) the low spatio-temporal resolution of chromatic systems compared with that of a luminance system;(2) the decolorization in the peripheral visual field;(3) the deterioration of color discrimination, caused by aging or several types of color deficiencies;(4) the wavelengthdependent loss of luminance, caused by aging or several types of color deficiencies;(5) the lower spatiotemporal resolution for yellow and blue relative to red and green.
Our study sought to establish a universal and comprehensive method for evaluating the visibility of the human face. This paper examines the peculiarity of the 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 of the human face.
Our study evaluated the lighting environments in offices, including the trade-offs between various attributes. Conjoint analysis, common in the field of market research, was used to evaluate these trade-offs. The attributes were illuminance, light distribution, glare, design, cost, usage of natural lighting, and recycling (229 subjects participated). Consequently, the concept of office-lighting preferences can be understood quantitatively. That is, part-worth utilities and attribute importance for all subjects showed the general characteristics of office-lighting preferences. Moreover, comparing groups of subjects according to attribute importance or the subjects' characteristics suggested valuable methods for understanding office-lighting preferences in depth.
We investigated ballast for electrodeless lamps operating at 13.56 MHz. Higher-efficiency ballast circuits are required because of problems at high frequency. Our investigation focused on class-D circuits. We applied numerical model analysis and conducted experiments to determine the conditions that maximize efficiency. These conditions occur when the output current is simultaneous zero and the voltage across the switching device is virtual zero. We found that the virtual zero of the voltage is the crossing point between the zero line and the extrapolation line of the voltage slope.
The National Police Agency has yet to propose detailed specifications for preventing signal head phantoms; they are currently being examined by the agency. The pedestrian signal head developed by our project satisfies the standard for the luminous intensity distribution specified by the agency. With this film type of pedestrian signal head, the ratio of signal light to sun phantom was found to be three times as that of much as current pedestrian signal heads.
Under fluorescent lamp illumination of 500 lx, 429 Munsell color chips were used in a categorical color naming using 11 basic color terms to test how colors appeared to change when young subjects wore filters that allowed 20-year-olds to see the outside world as 80-year-olds do. The results revealed no significant difference in categorical color naming in terms of apparent-color or surface-color perception. This suggests that old people can recognize blue colors for example despite the ocular-spectral-transmittance change of their aging lenses, and that the color constancy mechanism plays a critical role in color appearance compensation for older people.
“Visual clarity” is considered one of the most important characteistics of the color rendering properties of light sources, however, it cannot be adequately estimated by using the present CIE or JIS Ra method. For this reason, we previously studied the cause of visual clarity and found that visual clarity was caused by the feeling of contrast between colored objects under illumination, and proposed a new index of the feeling of contrast for a light source that uses the non-linear color appearance model by Nayatani et al. The purpose of the present study is to propose practical method for calculating and indexing the feeling of contrast for a light source that uses the CIELAB color space and CIE chromatic adaptation equation instead of the non-linear color appearance model by Nayatani et al. A new practical index of the feeling of contrast for a light source correlated well with one obtained using the non-linear color appearance model. Use of this proposed method with the CIE/JIS Ra method will make it possible to estimate the color rendering properties of light sources more accurately.