International projectionist (Oct 1931-Sept 1933)

September 1933 INTERNATIONAL PROJECTIONIST 23 TABLE V Summary Table of Data Lamp Type High IntensityHigh Intensity High Intensity High Intensity (HiLo) Low-Intensity Reflecting Arc LowIntensity Reflecting Arc High-Intensity Alternating Current Positive Carbons Negative Current Amperes 16-mm. H. I. Vi6"-V2 " Orotip 145-150 13.6-mm. H. I. Vs "-Vie" " 115-120 11-mm. H. L Vl6"-V8 " " 85-95 9 mm. Vie" 60-85 12-13-mm. SRA 8-mm. SRA 28-42 10-13-mm. Reg. MA 7-10-mm. Reg. MA 16-30 Screen Light Arbitrary Arc Units Same Voltage Line Watts Screen Size 75-80 16700-17300^ 60-70 13200-138002 110-190 50-60 9800-109002 45-55 6900-98002 80-140 55 3000-4600' 2000-29005 55 1600-3450' 1100-22005 60 40-60 7-8 mm. 60-80 23-28 1450-2350* 40-85 1 115-volt line, with resistance between line and lamp. 2 Either 115-volt line with resistance between line and lamp; current at 90 volts to resistance and lamp. ' Either 115-volt line with resistance between line and lamp; current at 85 volts to resistance and lamp. * A-c. line with transformer, 95 per cent efficient. ^ A-c. line with rectifier, 75 per cent efficient. or motor-generator set, 80 per cent efficient, delivering direct or motor-generator set, 80 per cent efficient, delivering direct occur in any degree with the new a-c. carbons? Mr. Downes: I do not want to say that there will be no trouble with this new arc system; but such difficulties as are encountered will be only those more or less minor annoyances commonly found in all projection systems. You certainly will not have the difficulties encountered with the old a-c. arc, as the new arc is entirely different. Mr. Richardson: Another important consideration is the possible effect upon light tone. The old-style a-c. arc furnished a rather harsh light tone; and the light appeared to be very penetrating, much more so than light from a d-c. arc. s Mr. Downes: We have had many requests from the smaller theaters such as: "Can't you give us the same bluev/hite light the larger theaters have?" There seems to be a general consensus of opinion among the projectionists that the blue-white color is far more desirable than the other. Mr. Richardson: Are those carbons ready for the market now? Mr. Geib: Yes. Mr. Richardson: What is the amperage of the two lamps? Mr. Downes: The power consumption at the arc is the same; the one we are demonstrating consumes between 40 and 45 amperes at 18 volts. EFFECT OF CURRENT EFFICIENCY OF THE life of an exciting lamp is very short compared with the ordinary house lamps, due to the special design necessary. The amount of light reaching the photo-electric cell, after passing through the optical system with its slot, is small compared with the total light radiated by the lamp; and as there is no way to increase the amount of light other than to increase the brilliancy of the lamp, the filament has to operate at an extraordinarily high temperature. A small increase or decrease in operating amperage changes the brilliancy of the light considerably, as is shown in the accompanying tables. To make these tables applicable to different types of lamps, the variation is given in terms of percentages. The brilliancy of the light is determined by the temperature of the filament, and this temperature in turn depends upon the current. The table Current 85% 90 95 100 105 Light 35% 52 73 100 134 Light output compared with operating VALUES ON LIFE AND EXCITER LAMPS shows that even with the comparatively small reduction of 5% in the operating current, the drop in light output is 27%. This means that the corresponding gain has to be added in the amplifier of the sound system. By comparing the percentage of light loss between various lamps operating at different voltages, we find that the life of the 10% overloaded lamp approximates only one-third the life of a similar lamp operated at rated voltage. These facts are well known and have resulted in many projectionists burning their exciter lamps slightly below the listed rating. A lower rating, however, gives equally poor results in the way of efficient performance, and it is for this reason that lamp manufacturers insist that their product be burned at the listed rating. At high temperature the tungsten filament of an exciter lamp evaporates, and the higher the temperature the 110 115 Current 90% 95 182 240 Life 380% 240 amperes higher the rate of evaporation. This action is the cause of the discoloration of lamp bulbs, occasioning serious loss of light. Under normal operating conditions, the evaporation of tungsten from the filament reduces the diameter of the filament wire, resulting in a progressively higher filament temperature. If, now, to maintain the volume of sound and offset the effects of discoloration the voltage is raised, the process of discoloration increases much more rapidly. Under these conditions it will be necessary to periodically increase the voltage, the effect of which will be to render the lamp useless within a very short time, either through excessive discoloration or a burnt-out filament. These facts relative to proper exciter lamp operation are self-evident and can be checked by any projectionist right in his own theatre. The economies effected by departing from the standards set up by the manufacturer are indeed of a petty nature in comparison with the risks taken on the score of efficiency and safety. 97.5 100 102.5 105 110 115 160 100 56 30 10 5 Life of lamp compared with operating am,perages