American cinematographer (Aug 1933)

August 1933 9 American Cinematographer 131 New Development In Carbon A rc Lighting by Elmer C. Richardson of Mole-Richardson, Inc. P ROGRESS in the development of carbon arc lighting equipment for use in motion picture production was retarded by the introduction of panchromatic film, the sensitivity of which was so well adapted for photograph- ing with filament light source. The photographic requirements of a new color process, developed by one of the leading firms in this field of pho- tography, seem to be best met with carbon arc lamps. The Sun Arcs and 80 ampere Rotary Spots used by many studios in combination with incandescent lighting have been suit- ably silenced so that they can be operated in conjunction with sound recording apparatus. However, for the new color process there being no satisfactory general lighting unit, the firm of Mole-Richardson, Inc., was requested to develop a broadside lamp which would meet the following specifications: 1. The lamp to produce an illumination level of 200-foot candlepower as measured at fifteen feet with a standard Weston photometer. 2. ’ The lamp being required for general illumi- nation purposes must have a comparatively flat distribution curve over a projection angle of sixty degrees or more, and the field of illumination to be devoid of any hot spots, i.e., areas of illumination which are photo- graphically objectionable 3. The feeding mechanism of the lamp to be so designed as to give a reasonably uniform level of light intensity during its period of operation, and the spectrum of the light emitted is not to show any alteration of its characteristics during the period of operation. 4. The lamp to be silent in operation so that it may be satisfactorily operated in conjunction with modern sound recording apparatus. 5. The lamp to take a form, and be so mounted that it will be convenient for placement, and to be of such weight as to be easily handled on the set. 6. The lamp to be economical in operation both as respects attendance and the consumption of currents and carbon electrodes. The requirements set forth in this specification demand a type of equipment far superior to any type of broadside lamp heretofore supplied to the industry. Mole-Richardson, in the design of their new 40 ampere Type No. 29 Twin Arc Broadside lamp, have not only met the specifications, but in a number of instances exceeded them. The lamp, which is illustrated in the accompanying pho- tograph, has been designed for operation at all times with cover glasses to eliminate the possibility of injury to the eyes of the actors. The diffusion glass which is supplied with the equipment has a high lead content which impedes the transmission of ultra-violet light, which is the compo- nent of arc radiation which causes the inflammation of the eyeball popularly known as “Klieg eye.” When equipped with cover glasses these lamps produce more than twice the illumination afforded by the old types of side arcs of simi- lar current capacity when operated open, and produce a very smooth field of illumination. The area of the aper- ture of the lamp has been made larger than was that of the old type equipment, so that though the lamps are of higher intensity the illumination is so distributed as to be comfortable to the actors in the set. It was characteristic of the old broadside equipment that at the time it was initially switched on, its intensity was at the maximum, and after operating for three rr four min- utes the level of intensity would drop thirty or forty per cent. In operating the color process for which this equip- ment has been developed it is most desirable, that at all times during the photographing, the level and quality of illumination be uniform; to comply with this requirement a rather unique principle of arc control has been devised for this new lamp. The old type of broadside struck the arc and maintained the position of the carbon electrode by means of a single (Continued on Page 151)