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High Intensity Arc — Benford 91
paper entitled "Can the Efficiency of the present Condensing System be Increased?"
I should like to ask Mr. Benford why it was necessary in the original Beck high intensity arc lamp to "cool" the positive carbon by "heating" it in an alcohol flame; and why it is no longer necessary to do this in the present type of lamp?
Dr. Sheppard: Has Mr. Benford any data on the absolute amount of ultra-violet energy between 3000 and 3500 with the lens in position?
Mr. Powrie: What is the object in using a third electrode of copper in a high intensity arc?
Mr. Bexford: Regarding the speed of the 150 ampere positive carbon, the speed of rotation was set at 16 revolutions per minute, and we never found that the light was very much influenced by changes of two or three revolutions a minute either way. I believe the 75-ampere arc runs at twelve revolutions a minute, and I must confess that I do not believe the quantity of light will be greatly changed by lowering the speed to, say, eight revolutions a minute.
In regard to the proper voltage of the 150 ampere arc, it is usually set between 75 and 80 volts at the arc. You may increase this and run the voltage up to 85 or 90, in which case there will be a small increase of light, but the arc becomes unstable. You can gain light and lose in stability, and it is an engineering choice as to where to stop, and the General Electric engineers think 75 to 80 volts is the best all around voltage.
Mr. Palmer: In maintaining the arc voltage, is a sufficient accuracy maintained or would j^ou have to measure the amperage?
Mr. Bexford: The automatic lamps are built to maintain current by means of changing the arc length. If you change the line rheostat the arc changes length. We selected this because the light is more sensitive to current than voltage, and we thought this would give the most uniform condition of light.
Mr. Richardson asked about contemplated changes in color. We have not done anything on this, and I don't think anything is under consideration. We feel that the most light is the best, and if the tone is not right, we can correct it by means of filters.
Mr. Richardsox: Do j^ou mean that it would be impossible to change the tone without decreasing the illumination value?
Mr. Bexford: Almost that; we cannot be quite certain, but we have searched for the most light.