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354 Transactions of S.M.P.E., Vol. XIII, No. 38, 1929
Mr. Manheimer : In the larger type studio lamps, I would like to know what is the actual burning life, and what is the economical burning life?
Mr. Egeler : These lamps have an average burning life of one hundred hours. The theoretical most economical burning life is probably somewhat greater, but there comes in the factor of mechanical breakage, and color quality of the light and the space limitations for the equipments are the governing factors.
Mr. E. H. Richardson: Is nothing being done to develop a lamp with a longer burning life?
Mr. Egeler : We can design a lamp for practically any life, but for .a given light output, increase in average life is obtained at the expense of increased wattage.
Mr. Richardson : We are still using some with the tip on the end. The actual losses in these lamps have been in only very exceptional cases from blackening. The losses in these lamps have been mostly thru handling and packing. Most of the damage done is in loosening the bases, and damage due to jars where the mechanical structure is broken down. Here is the answer to that. The lamp is actually better even after 100 hours than before. Moisture has gone, and all the oxygen left has been absorbed. When the lamp is cleaned it is a most excellent product.
Mr. Wright: It may be of interest to know that the idea of cleaning the inside of incandescent lamps is an old one. We find it was tried in connection with the old carbon lamp. I understand Mr. Roger Hill did some work on it about ten years ago in connection with the motion picture projection lamps. He suggested sand. I believe sand attacked the filament and caused early burn outs. Recently Mr. L. C. Porter brought to my attention the work done with the sand cleaner at that time. The development of a tungsten powder cleaner has successfully solved the problem. Along with this development of removing the blackening has come the development of an improved non-sag tungsten filament wire. These two developments have combined Avonderfully to give us this large increase in efficiency.