This study aims to clarify whether the difference in light source (white LED and fluorescent lamp), affects the readability of various colored text on various colored backgrounds. We also investigated whether the readability of color letters was different for readers under of different ages. Test stimuli with 20 color combinations were compared in terms of their readability by elderly readers under each type of lighting. Test results showed that the lightness difference of colored text varied under different lighting and affected its readability. Meanwhile, result of an experiment using nine color combinations by blue or red with the young and elderly subjects confirmed that age affects readability. This might be due to the reduced sensitivity to lightness of elderly subjects not only in the short-wavelength region but also in the long-wavelength region.
“Light pollution” due to outdoor lighting results in delayed heading time and reduced yield in rice. The purpose of this study is to assess the effect of light pollution by using a method whereby rice grows in a climate chamber and white LEDs (light emitting diodes) were used to simulate as outdoor lighting. We estimated heading time by quantitative determination of floral activator Hd3a in rice when five LEDs irradiated Oryza sativa L. cv Koshihikari in a dark period. As a result, three commercially supplied lights (light sources 1-3) and a customized light (light source 5) noticeably suppressed Hd3a expression and the estimated heading was delayed more than four days, indicating the occurrence of light pollution under 5lx irradiation. However, another customized light (light source 4) did not suppress Hd3a expression and estimated heading delay was within three days, indicating a reduction in light pollution. This stemmed from the difference in photon flux density with which each light source irradiated the rice. This suggests that illumination, in which light pollution is reduced (light source 4), of illuminance up to 10 lx does not suppress Hd3a expression, whereas over 15 lx does suppress Hd3a expression.
The revealing power was proposed as an index to evaluate visibility in road lighting. However, applicability in tunnel lighting has not been studied. We evaluate the tunnel lighting visibility on the basis of the revealing power in this paper. Our simulation and field experiment, made clear the relationship between the brightness and overall uniformity of the road surface and revealing power. This result confirms tunnel lighting can reduce the road surface luminance while maintaining visibility and can also save energy.