The American cinematographer (Jan-Dec 1928)

January, 1927 AMERICAN CINEM ATO GRAPHER Seven & M. P. E. Transactions Discussion On "The Tungsten Lamp Situation In the Studio" [TAm paper, read at the Lake Placid convention of the S. M. P. E., uas published in full in the American Cinematographer for November. ■ — Editor's Note.] MR. BEGGS — About a year ago I tried to calculate the theoretical costs of lighting a studio with mazda lamps. At that time it was felt that mazda lamps were impossible, but calculations made theoretically showed that the costs were approximately the same as for arcs. Now, the film is a little faster for incandescents, and labor costs have been calculated closer, so that the figures I published at that time do not necessarily apply for mazda lamps, although at that time it was about a toss-up for cost for lamps, fixtures and labor. Since that time we have been asked to produce a metal reflector. It is not so efficient as silvered glass, but it is indestructible, and chromium has been found to be the most successful plating. The advantages are chiefly that it is easily cleaned. Chromium is going to be very popular as a surface plating material. Probably you noticed that the Kodascope projector used it, and it is being used in the lighting field for industry. I should like to ask Mr. Farnham about the over-voltage operation of lamps. Any of these incandescent lamps can be burned with over-voltage with reasonable assurance that it will give fair photographic performance, but it may destroy the lamp, and there should be an agreement among studio engineers, I believe, concerning the exact over-voltage which should be used. Another point is the avoidance wherever possible of these extremely expensive lamps; $175 is the present price of the 10 kilowatt lamp with 100 hours' life. The same light flux can be obtained from ten 1000-watt lamps for $2.50 each, which gives a different total price, and it seems unreasonable that studio engineers should insist on using the very expensive lamps. I think they might get together a symposium on the use of incandescent lamps for studio engineers. MR. FARNHAM — With reference to operating lamps at an over-voltage, the studios now working with incandescent lamps operate them from the same source of supply that they operate their arc equipment, and hence it is not practicable to operate the lamps at other than the voltage of the circuit without causing trouble on other sets that are using the same source of supply. The light output of an incandescent lamp operating at from 250 to 400 hours' life has the correct color characteristics for use with the Panchromatic film, and if they were operated at an over-voltage a relatively greater increase in the blues and violets would result, and the color renedition would not be correct. Instead of overvoltaging a lamp at the time the picture is being taken, I would suggest the practice of operating lamps at an under-voltage during rehearsing and at times when it is not necessary to expose the film, and then before the picture is to be taken the lamps should be brought up to normal voltage. In considering future practice where the lamps are operated directly from alternating current source it would be a simple matter to install a portable induction regulator between the supply circuit entering the building and the particular set on which it is desired to control the current. This would make it possible to operate the lamps at an under-voltage until the time to make the picture, when they could be quickly brought up to full voltage. The use of this device would likewise permit bringing lamps from total darkness to full brilliancy or from full brilliancy to total darkness for special lighting effects, By Peter Mole duplications of sunrise and sunset scenes, etc. With reference to Mr. Beggs' point that it would be more desirable to use ten 1000-watt lamps instead off one 10,000-watt lamp; this might be practical in some cases, but there are many instances where it is desired to create the effect of strong sunlight streaming in through a window or door, the intensity of this source must be considerably greater than that of the other light source illuminating the set. For this purpose a single source of high-wattage such as 10-killowatt lamps would be required. Ten 1000watt lamps would be quite out of the question because they would create ten individual shadows and spoil the illusion of sunlight. MR. ISAACS — I should like to ask Mr. Farnham what the advantage would be of cutting back from DC to AC when the latter gives flicker. MR. FARNHAM — A mazda lamp operates equally well on alternating or direct current. The studios would naturally not wish to discard their existing motor generator sets, but as the present equipment becomes obsolete or greater lighting capacity is required, they would gradually shift to AC operation and thus remove the heavy investment in substations and the necessary attendant which rotating equipment requires. With regard to flicker on alternating current circuits due to the relatively small size filament wire of the 100-watt lamps and those of lesser wattage, there is a noticeable flicker when the lamps are operated on 25-cycle currents. On 60cycle currents this flicker canno+ be detected with the eye, but it can be observed by stroboserpic methods. However, as we increase the wattage of the lamps and hence the diaineter or mass of the filament wire, the heat storage capacity of the filament becomes greater and the fluctuations of the light, due to the cyclic variations of the current, becomes less. From tests which we have conducted using a special stroboscopic device, we find that fluctuation of the light disappears with lamps of 500 watt, 115 volt ratings and above on 60 cycle circuits. In the studio district 50 cycle circuits are the rule so that it is probable that the 750 watt lamps would mark the dividing line between flicker and non-flicker. Since all of the lamps employed in studio lighting service are of 1000 watts and above, I can assure you that there will be no possibility of flicker caused by the shutter getting into synchronism with the alternating current cyclic changes. MR. BAUER: Some years ago Westinghouse went into the problem of sufficiently heavy filaments in incandescent lamps. As Mr. Farnham says, it frequently happened that the synchronism mentioned was noticeable on the screen as a decided flicker. The result of their investigation was that they brought out a transformer with 20 ampere 20 volt light which is equivalent to 400 watts. In an ordinary 400 watt incandescent lamp, the flicker would persist, but with the 20 volt 20 ampere lamp, the filament was sufficiently heavy to prevent this. MR. CRABTREE: I should like to mention that in the studio in Rochester for taking color motion pictures it is our practice to burn the lamps at under-voltage during actual exposure. This is done by means of rheostats. MR. BEGGS: All the prize fights are photographed in the light of incandescent lamps. At Chicago they used 44 one thousand watt lamps in 44 reflectors. These burned at normal voltage and were of the ordinary type (Continued on Page 16)