A Consideration of the Screen Brightness Problem--

The great interest that the problem of optimal screen brightness holds in motion picture engineering is proved by the numerous researches on the subject in recent years. Besides the very interesting American papers published in this Journal, some recent German works are worthy of consideration. - In 1936 Zimmermann determined the dependence of the visual effect upon the screen brightness and found that a maximum value is attained at about 14 foot-lamberts. He investigated also the influence of light distribution, and temporary brightness changes. Finally he pointed out that the time the eye needs to see all recognizable contrasts varies, according to the brightness level, between 1/3 and 1/10 second. - In 1936 Rieck verified, under conditions similar to those in cinema theaters, the character of the contrast-sensibility relation that Brodhun and König had found in their classical research. - Very recently H. Frieser and W. Münch reported results obtained by projecting a detail test-object. They determined the contrast threshold function under conditions very similar to those of actual projection. They did not find a material increase in the number of distinguishable contrast steps for picture brightnesses exceeding 10 foot-lamberts. - It is to be hoped that the consideration of the results of (111 these investigations will form a basis for early temporary screen brightness standardization.