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The Interior Illumination of the Motion-Picture Theatre
By L. A. Jones
The desirability of providing sufficient illumination for the convenience and comfort of the audience, if this can be accomplished without perceptible loss of quality in the projected picture, is obvious. It is scarcely necessary to enumerate the many serious objections to the use of very dimly lighted rooms in which motion pictures are being exhibited to large audiences. The difficulty encountered by persons entering from the relatively brightly lighted exterior regions in finding their way to unoccupied seats is considerable. The undue strain thrown upon the accommodation processes of the retina resulting from a sudden transition from a brightly lighted exterior to a dark interior, or vice versa, is very objectionable and to be avoided if possible. More serious than these, however, is the excessive visual fatigue "and eye-strain resulting from a prolonged observation of a brightly illuminated area (such as the screen on which the picture is being projected) occupying but a small portion of the field of view and surrounded by very dark areas, this condition being ideal for the production of glare effects due to excessive contrasts. It is evident for the satisfactory exhibition of motion pictures that the general illumination in the theater must be subdued in order that the projected picture shall be of good quality as regards its apparent brightness and contrast, and that in raising the value of the general room illumination there is a limit beyond which it is impossible to go without seriously affecting these characteristics of the picture. However, it has been found by proper distribution of the light that the general room illumination can be raised to a value sufficient to eliminate all of the objections to a dimly lighted theatre and at the same time produce no perceptible injurious effect upon the quality of the projected picture.
The object, therefore, with which this work was undertaken was the determination of the maximum value of general illumination allowable in a theatre when motion pictures are being exhibited, this allowable maximum being defined as the highest value of general illumination which will not cause any appreciable diminution of apparent contrast in the projected picture. From a consideration of the fundamental data available relative to the various retinal sensibilities, it is possible to draw certain general conclusions as to the most desirable conditions of illumination for this purpose. The data available, however, are not sufficiently complete to permit the computation of the desired values, and hence it was necessary to resort to experiment and actually to measure in an experimental installation the illumination which was found to be permissible without causing loss of quality in the projected picture.
Before proceeding with an account of the experimental work, it may be well to consider briefly the general theory of the subject, and the fundamental characteristics of the eye which are important in problems of this nature. First of all, it should be borne
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