Journal of the Society of Motion Picture Engineers (1930-1949)

Feb., 1932] PROJECTION SCREENS COMMITTEE 251 the average lies between three and five foot candles; and with low intensity light sources, three foot candles. In the studio laboratories where prints are analyzed by the studio personnel, intensities of about thirty foot candles are used — ten times the intensities used in the theaters. This is the cause of dark prints and the troubles that go with them, such as overloading. Dirty screens also require overloading, causing additional loss of picture quality. MR. FARNHAM: In connection with the data on reflection factors of screens, the figure of eighty per cent appears to be very high. I should like to ask if that is absolute reflection, i. e., incident light to total reflected light or is it the ratio of reflected light after a period of use to that of a new screen? MR. WOLF: The measurements of reflection factor were made as soon as the process was completed; each time a comparison was made with the standard. MR. FALGE: It happens to be the brightness at the normal which is hi question rather than the total reflection value. MR. FARNHAM : That is an extraordinarily high value, and that is why I asked. PRESIDENT CRABTREE: Have the experiments of the Committee, Mr. Wolf, gone far enough that we can begin to think of recommending a standard of screen brightness? MR. WOLF: The data collected at the demonstration at Bell Laboratories proves more or less conclusively that there are certain limits to be considered. We cannot say definitely what they are, but they probably lie between seven and thirteen foot candles. We definitely believe that any picture having a brightness less than seven foot candles is certainly too dull ; and any picture having a brightness greater than thirteen foot candles is glaring and disagreeable to look at. PRESIDENT CRABTREE : Can any one explain why a value of thirty is used in the screening room? MR. FALGE: In an article published by Mr. Huse some time ago, describing some tests of Hollywood screening rooms, he gave the value as thirty foot candles. It is expected that the intensity will always be high in the screening rooms, unless deliberate attempts are made to keep it within reason, because the picture is always small and the light intensity is greater than in the average theater. PRESIDENT CRABTREE: Were Mr. Huse's measurements strictly comparable with yours? In other words, has the Committee first of all found a method of getting an absolute measure of this reflection value? Does your figure of ten correspond with a similar figure in Hollywood? MR. FALGE: I think you will find considerable variation among the figures that have been collected; but I think it is sufficiently important, even with an error as great as twenty-five per cent, to show that the values in the theater differ considerably from those in the studios. MR. FARNHAM: As a result of some work that I did a number of years ago on screen brightness, I found that there is also a relation between the picture size and the screen brightness. Smaller screens should be brighter for the same projected picture, so that whatever intensities we recommend for the studio viewing rooms, they must be corrected for the size of the picture. PRESIDENT CRABTREE: That was also observed when we were making widefilm experiments. We did not need as great a brightness as with the smaller pictures. MR. GAGE: May I ask if the foot candles are measured with a machine sta