British Kinematography (1948)

165 AUDITORIUM LIGHTING L. Knopp, Ph.D., M.Sc, F.I.E.S., F.B.K.S.* Is it likely that a degree of auditorium lighting, sufficient to make unnecessary the use of torches, will be realised in this country ? IN dealing with this question, there are several factors to be considered. First is the human eye, which is a very complex mechanism ; it is capable of visual perception at illuminations from 1 /500th foot-candle up to 1,500 foot-candles or more. Throughout this range the visual acuity is not constant, nor can the eye immediately accommodate itself to widely different light intensities. Therefore, regard must be paid to the period of time necessary for the eye to become adapted to the low intensity of illumination in the auditorium. With persons coming from bright sunlight into an auditorium, I would say that it is not possible to have the necessary high degree of illumination in the auditorium to enable them immediately to see the way to their seats. If, however, we provide for a delay before reaching the auditorium, or if we consider persons entering a kinema at night time, the problem is comparatively simple. The period of time required for dark adaptation could be provided by a foyer or an entrance corridor of sufficient length and with a suitable diminution of brightness of illumination, so that the eye could accommodate itself to the level of the illumination. Some time ago, measurements were made in several London kinemas and it was found that the degree of illumination with safety and primary lighting in operation, without the picture on the screen, averaged .01 footcandles. Tests were carried out under the auspices of the Illuminating Engineering Society to find the degree of illumination necessary for a reasonably dark-adapted person to see his way to his seat without the use of a torch. It was found that, to do this, the illumination at the point of his entrance into the auditorium should be not less than 0.8 foot-candles white light uniformly distributed. If we proposed to provide coloured lighting, lamps of higher wattage would be required ; a flame-coloured lamp would have to be twice the wattage, green five times, red sixteen times and blue no less than 39 times. This brings us to the next consideration. What is the maximum illumination one could have in an auditorium without impairing the quality of the projected picture ? Many tests have been carried out and it has been found that if the average screen illumination is approximately 100 times that of the average level of auditorium illumination, then the effectiveness of the picture is not impaired provided, of course, that the screen is protected from stray light. The precise proportion is given by the formula : — Es —2.5 _ 100 " h& It should be mentioned that this level of .08 foot-candles white light found to be necessary is dependent upon the decorations of the auditorium being of a reasonably light colour and that there is a suitable contrast in the colour of the seating and carpeting. This level of illumination was also determined when the screen illumination was not less than 11 foot-candles with the shutter running, but without film. I am afraid that it will be a very long time before kinema auditoria are illuminated to this high level. Mr. R. H. Cricks : Mr. Knopp might clearly if chairs were fitted with white have stressed more the influence of colour plastic arm-rests. They would not be and contrast. It has often occurred to seen by patrons when seated, me that patrons could see their way more Mr. R. Pulman : They would often be ♦Cinematograph Exhibitors' Association