1995 Volume 79 Issue 2 Pages 78-84
Various kinds of large-scale membrane structure have recently been constructed and utilized for multiple purposes, such as baseball stadiums. In a baseball stadium it is important to create a suitable visual environment for both players and spectators to see the ball.
An experiment was carried out inside a membrane structure to examine the factors that affect the visibility of flying balls and the threshold luminance contrast for the ball, that is, the visibility of the balls hit by a machine was subjectively evaluated by observers. In the experiment, the luminance of flying balls and the background and other conditions were set at various appropriate levels. Luminance contrast C of the ball was defined as
C=LT-LB/LT(for LB<LT)-LB-LT/LB (for LB>LT)
LT: luminance of ball
LB: luminance of background.
The major results obtained in this experiment are as follows:
(1) There is a linear correlation between evaluations of visibility of flying balls and luminance contrasts of the balls.
(2) Under positive contrast conditions, the threshold luminance contrast of the ball is 0.3. For negative contrast, it is 0.4.
(3) Under relatively light backgrounds, the evaluations are almost the same whether the contrast is positive or negative if the absolute values of both contrasts are the same.
(4) Under negative contrast, the visibility is evaluated as being lower for low background luminance.
(5) As the angular velocity of the balls decreases, the evaluated visibility increases.
(6) The visibility of flying balls is not influenced by ball color.
(7) If the hitting point of the ball is not visible, the evaluated visibility decrease as compared with the visible case when luminance contrast of the ball is low.
