Effects of Luminance of Light Source Illuminating from Behind on the Visibility of a Moving Object

Abstract

LED lighting sources have become widely used in various illumination settings. The purpose of our study is to clarify the effect of luminance level of LED light sources on the visibility of a moving ball. The light was falling on the observers’ fovea and 5 luminance levels from 1^＊10⁴ to 30^＊10⁴ cd/m² were prepared. The ball size was 0.16 or 0.25 deg in visual angle. Observers pursued a falling ball in front of the light source, then responded by a two-alternative forced choice (2 AFC) method whether they could detect the ball or not. In addition, observers responded whether they could see the falling ball in whole or partially on the light source, and the apparent size of the ball if observers could detect a ball. The results showed that the probabilities of disappearance increase with luminance levels, and that the probability of disappearance for smaller balls is higher. Balls more frequently appeared partially and smaller with increasing luminance levels. We derived psychometric equations for the probability of the ball-disappearance phenomena as a function of luminance of light source, suggesting that the luminance threshold is around 30^＊10⁴ cd/m².