Since there is much achromatic information in an actual visual environment, the effect of color on visibility must be considered when estimating the visibility of signs, objects, and lighting in the environments. We investigated the relationship between the recognizable threshold of form perception and three color factors (value, hue and chroma) by conducting an experiment using Landolt’s eye chart of 14 color conditions under three levels of background luminance. We measured the individual visual acuity of six subjects in two age groups (young and aged). When the test chart contrast was more than 0.5, only the value affected the recognizable threshold of form perception; the chroma and hue had no effect regardless of the background luminance or individual visual acuity. Therefore, two concepts defined in our earlier studies, “visual acuity ratio to the maximum level of individual visual acuity” and “relative acuity incorporating individual visual acuity into the target size”, hold if the colored target contrast is 0.5 or higher. The concepts do not hold if the target contrast is less than 0.5 because of the effect of color identification.
It is very useful when judging lifetime of a lamp to know the position of the spot on the electrode filament. This is because the lamp’s life depends mostly on the emitter volume which decreases as the operating time increases, and the remaining emitter volume is closed to the emission point. We describe an easy method for finding the emission point. This research was conducted from two viewpoints, experimentation and simulation. We observed the emission point and measured the lamp’s electrical characteristics, which are the voltage across the filament and the currents flowing into and out of the filament. We then estimated the emission position using the electrical characteristics measured as a simulation. Our observation results showed that the position of the spot can be confirmed during the cathode cycle but not during the anode cycle. Our calculations showed that the spot position moves as the lighting time increases in the cathode cycle, but that it does not move during the anode cycle. There is no discrepancy between our observation results and our calculation results.
Luminaires that use high power LEDs are the most common kind in general use. To attain the desired brightness for practical applications, several of LEDs are required. Combining the luminous flux from each LED efficiently is important to control the light distribution. To do this, we fabricated a luminaire and obtained both the desired uniform light distribution and good uniformity of chromaticity over the whole light distribution.