British Kinematography (1951)

52 BRITISH KINEMATOGRAPHY Vol. 18, No. 2 wof one-third without in any way embarrassing the lighting cameraman. Cost of Providing and Maintaining Lights It is instructive to consider the effect on a studio if such a change in practice were well established and were applied to all films. The studio would need, for the service of all its stages, a greatly reduced number of arcs, and only a proportion of them need be equipped with ballast resistors, while there would be a saving of about 40% on the total amount of cable required. The time taken completely to overhaul an H.I. arc spot is about 13 hours and does not vary much from one size to another; the reduction in the total number of arcs required by a studio would, therefore, effect a substantial saving in maintenance. There are other economies, over and above this, which can be effected by the latest equipment. Due to the burning hours counter, arcs may be overhauled after a predetermined amount of use, thereby increasing their reliability, reducing troubles on the set and eliminating unnecessary work. The demountable mechanism considerably reduces the overall cost of overhaul and will also enable the mechanism to be kept cleaner. Other features in the latest designs include the following: 1. Visible warning 13 minutes before carbons must be changed and the ability to do so in 20 seconds without disturbing the setting of the lamp; also the ability to change the complete mechanism in 30 seconds. 2. Arc image periscope to ensure correct setting and silent steady burning. 3. Polarity indicator to assist cabling and to prevent delays due to damaged craters. These factors will tend to reduce delays during shooting, but no data are available to enable the average saving to be estimated. Future Developments In addition to showing the benefits which are now available by the adoption of the recent developments which have been discussed, the data also contain some indication as to the future trend of development. Table I shows the trend in arc development and the increased economy of the more powerful lights. Finality has by no means been reached, and the next arc which will be made available as soon as there is a demand for it is the Mole-Richardson Type X6, the performance of which is indicated ac the foot of the table. It will be seen that its efficiency, as measured by its cost of operation for equal light output, is consideraoly better tnan that of the present largest arc. A spot of this enormous power, equal to some ten 150-amp. arcs, will probably be too powerful for widespread use on the average studio set, but may be of great value on the largest sets and also on location. The economy due to series running is, in a sense, fortuitous, because it arises from the fact that 115 volts is an inefficient supply voltage for the smaller arcs and results in undue loss in the ballast resistance. Though finality has not been reached in the development of arcs, as evidenced by the Type X6, there is no probability, as far as can be seen at the moment, of a comparable advance with other types of light source. The estimates which have been discussed cannot be exact, but their probable error is small compared to the economies which can be expected. It is apparent that relatively little capital expenditure will be required in order to obtain the full benefit of these modern developments. Influence on Studio Design The influence of series-parallel running on the design of future studios is worthy of discussion. The " Mole float," the practicability of which has been demonstrated tonight, may be regarded as a simple expedient for the conversion of a 115 volt circuit to a 3-wire system, with 115 volts across the outers and 57J volts between outers and " Mole float," but, as the " Mole float " is not connected to the generators, balance can be maintained only by controlling the load. This is not particularly difficult, because experience has shown that an out-of-balance not exceeding 10% causes no ill effects. This raises the question whether, when a new studio is being designed, it would not be wiser to install a normal 3-wire system, but with 115/57J