Transactions of the Society of Motion Picture Engineers (1925)

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High Intensity Arc — Benford SPECTROPHOTOMETF^IC TEST HIGH INTENS/TYANO PLAIN CARBON SEARCHLKjHT BEAM OATA BYCG/^BBOT 1.30 I.ZO 1 10 1.00 0.90 \0.80 %0.70 ^OW ^0.50 "^0.40 0.3d 0.ZO a 10 0 ,'■< >f P^^ jNi ?^T, '9^^, ^^^ ^' "' >.^ , ■ — ..cjnf^"- — ■ — ■ ' ?£f ^li\\\ jH w ^^ ^ ^ y ^ ^ ^' O/li 11 u / r' / ^ y % X / t y < fe^ ^ A /■ ^ /' ^ 'A ^^, %■ ^-1 ' ^ , ^ r ^V/; ^ // / 1 1 ' O.mZO 40 60 dOO.500 ^0 40 60 800.60020 40 GO 60 0.700 20 4€ WAVE LENGTH /N M/C/^ON^ Fig. 18. — A spectrophotometric comparison of useful light from plain carbon and high intensity arcs. This analysis shows the influence of mirrors or lenses in absorbing the excess of violet. DISCUSSION Mr. Griffin: Will you outline for us what you have found with regard to the speed of rotation of the high intensity arc positive carbon? I ask this because we have taken over from the General Electric Company the manufacture of the high intensity arc for motion picture work; that is, the model they have formerly sold, and while we could formerly send all the complaints to the General Electric Company, we must stand on our own feet now. Some persons claim that if the speed is reduced to one-half that now used, much finer results are obtained. Our tests do not indicate that it is so serious, but the particular reason I have in mind for asking is that one of the lamps put out recently uses a lower speed of rotation. Mr. Palmer: What is the proper arc voltage in a 150-ampere lamp, and can we be sure that we are operating the lamp at its highest efficiency if we hold the arc voltage at that amount? Mr. Richardson: The principal objection to the high intensity arc has always been its harsh tone. May I ask what progress has been made, or what, if anything, has been accomplished in reducing