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120 Transactions of SM.P.E.,July 1927
Among the obvious advantages of this type of mirror are: cost, ease of repair, lessening of damage when overheated, greater economy of hght projection, and a superior type of distribution of the hght in the beam.
DISCUSSION
Mr. Porter: The type of reflector described is that designed for the relatively highly concentrated source of the arc; has Mr. Benford used a 10-kilowatt Mazda lamp?
Mr. Benford: In designing this mirror, if you want to do a nice job, you correct for the light source. In designing for a 40° incandescent beam, the mirror makes 36° width and 4° width are contributed by the light-source. One could work well with the incandescent lamp.
Mr. Egeler: From an artistic standpoint it seems undesirable to have extremely sharp shadows. In connection with the application of these units I should like to ask whether these relatively sharp shadows are not objectionable, and whether the units are not used with diffusers that eliminate the shadows. Is there an extremely wide spread of the beam with a sharp shadow or a good control of the light which is then diffused?
. Mr. Palmer: I can answer Mr. Egeler's question by saying that in the first place it isn't often that just one of these lamps is used at a time. In that case, one would help out the shadows of the other. If it was necessary to have a diffused shadow without showing the peculiar effect seen on the screen, it could be accomplished by putting a ground glass on the lamp for the time being. Even with the ground glass I believe one would get more light than from an ordinary parabohc mirror without the glass.
Mr. Jenkins: I should hke to ask if this same development has been appUed to elhpsoidal reflectors?
Mr. Benford: That would be entirely possible if you wanted to concentrate not to the maximum degree but over some definite area. I think that would be very useful, and I don't see any difficulty in carrying out the design.
Mr. L. a. Jones: I should like to call attention to a polygonal reflector which was described some time ago in these Transactions This was not designed from the same view point as that taken by Mr. Benford. The reflectors I refer to were designed specifically for flood light, that is obtaining fairly uniform illumination over a