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staring black-and-white of the text. This criticism calls to mind another correlated phenomenon — the change from brilliant light to the absolute or quasi darkness of the cinema halls, and to the possibility of making use of light screens referred to by Prof. Van der Hoeve.
The expression " in full day-light " is hardly applicable here, because screens of the kind work properly in a half-light or semi-darkness, and in any case do not require absolute darkness.
In this field also diverse more or less efficacious and practical systems suggest themselves; most of them make use of transparent screens, which often absorb a good deal of light. Others are based on a system which makes it possible to produce on the white surface of the screen a state of shadow deeper than the surrounding shade, a state close akin to darkness, in such a way as to present realistically the blacks of the projected image and to bring the light shades of the same into greater relief.
This system, though not free from practical drawbacks, seems to us likely to give the best results, as it allows of an intenser illumination of the auditorium, being based on the contrast of light.
As for the captions, it is necessary to obtain the highest degree of visibility from all points of the hall. This might be obtained by making sure that the text was in harmony with the normal vision of the spectator furthest removed from the screen.
This would apparently suggest the practical need of illuminating the captions more brilliantly, so as to show them up better on the screen; on the other hand, this would aggravate the contrast between the effects of the soft tones of the scenes and the startling tones of the titles. Another alternative would be to modify the form of the letters, which would complicate the presentation of the captions. All these difficulties, however, are on the way to being solved by the vocal film.
The other violent contrast consists in the jump from the darkness or semidarkness of the halls during projection to the lighting-up during the intervals. Apart from the possibilities of daylight screens in full or subdued light, the illumination of the halls during intervals and at the end of the show ought to be effected gradually or else by coloured lamps, which would not tax the eye-sight.
A French Review Protection, securite, hygiene dans V atelier, the monthly bulletin of the Association of French manufacturers for protection against labour accidents (Paris, No. 4, 1930), points to the results of experiments that have been made on the various degrees of light desirable in localities of different kinds.
The intensity is indicated as lux, corresponding to the average illumination of a superficies of one square metre upon which a source of light, lumen, is reflected.
The lumen in its turn may be defined as the quantity of light intercepted during a unit of time by a spheric superficies of one square metre, the whole of which at all points is placed at a distance of one metre from a source of light casting, in all directions, the light of one candle.
The degree of lux is generally measured by an apparatus known as a luxometer.
This Review recommends a light intensity of 30 lux for cinemas during intervals and of 1 lux during projection.