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1948-49 Theatre Catalog, 7th Edition, Page 411 (398)

1948-49 Theatre Catalog, 7th Edition
1948-49 Theatre Catalog
1948-49 Theatre Catalog, 7th Edition, Page 411
Page 411

1948-49 Theatre Catalog, 7th Edition, Page 411

New Motiograph-Hall 75 115 High Intensity Lamp

An Introductory Report that Promises Much from A New Basic Approach to Well Distributed Screen Brightness

The new Monograph-Hall 75/115 High Intensity Arc Lamp is claimed to provide an extremely brilliant light which should make it ideal for drive-in and large conventional theatres. Completely new and not generally released at press time, its announced features are described and data on its test performance given. Other information has to do with its economy and simplicity of operation. All iibugsii are said to have been eliminated by a yearas experimental use of the new lamp under actual theatre conditions.


The advent of the drive-in theatre with its tremendous 40 to 65 foot picture widths and viewing distances as great as 800 feet has created a demand for lamps that will give greater light output and better light distribution than lamps designed specifically for con. ventional theatre screens. While many reflector-type arc lamps and condensertype lamps have given reasonably adequate screen visibility in drive-in theatres with picture widths up to 40 feet and viewing distances up to 500 feet,

they have not provided the high, well distributed brilliance that the average patron has come to expect in motion picture presentations, or must have if he is to see the film without eyestrain. And at greater viewing distances, or under adverse weather conditions, the deficiency is even more marked.

To satisfy this demand Motiograph has specially designed and is now offering a new reflector-type high intensity are lamp operating in the 75/115 ampere range. Field tests indicate that these lamps emit sufficient light when operating at 85 amperes to meet the extreme demands for greater illumination for both drive-in and large indoor theatre screens. These new lamps owe their exceptionally vivid light to their unique employment of a rotating positive carbon never previously used in reflectortype lamps which permits their operation in the 75 to 115 ampere range. Without a rotating positive carbon even burning and a proper crater form was found to be impossible over 70 amperes.

Another reason claimed for the greater light output delivered by these new lamps lies in the precise positioning of the carbons with respect to each other. The method of positioning employed permits the gases to be retained within the crater where they become superheated and extremely brilliant. The ability of the large 16" mirroraone of the largest utilized in a reflector-type lamp

NOTE THE POSITIONING of rotating positive carbon and negative guide bar in the burner assembly.

etc collect maximum light also contributes to the greater light output. A device which maintains constant current and accurate focusing also'serves to produce maximum screen brilliance at all times.

High intensity condenser-type lamps burning large carbons at high amperages are capable of producing extremely strong light at the arc. But a by-product of this light is heat in large quantities. In fact there is so much heat that some manufacturers recommend the use of a glass filter between the arc lamp and projector to reduce the quantity of heat energy reaching the aperture in order to prevent the film from reaching temperatures which cause buckling and consequently ffin and out of focus" conditions, to say nothing of the deleterious effects on the film itself. Unfortunately, filters of this type materially reduce the visible light as well as the invisible heat energy. In most instances, then, even though the source produces a large amount of light, the useful visible portion of it reaching the screen is minis mized to varying extents. It may even be that only very little more than that which can be obtained from a lesser light source actually is used.

Because of the extremely high intrinsic brilliancy of the arc resulting from the arc controls in the new Motiograph lamp, the total light output contains a high percentage of visible light in proportion to effective heat radiation. Therefore, except in the extremely high amperages resulting from some extreme light demands, the need for a filter is eliminated. Motiograph lamps operating at 85 amperes have been installed with three different makes of projector mechanisms and while some run cooler than others, in no case has there been any operational didiculty nor any report of film damage. It is, however, recommended that external blowers such as those supplied with Motiograph AA projector mechanisms be used with the lamps to further reduce any possibility of film damage arising from heat.

Screen Brilliancy

Tests have indicated that these new lamps operating at 85 amperes produce 19,000 lumens of light. Some high intensity arc lamps operating at 70 ampcres will average 13,000 lumcns. In the Motiograph-Hall models, an automatic focus control, a combination optical and electrical device, constantly holds the crater of the positive carbon at the exact focal point of the mirror within the exceptionally narrow limits of 7/1000ths of an inch. This unique feature prevents possible variations in light intensity that might occur with lamps of less precise focus control.

1948-49 Theatre Catalog, 7th Edition, Page 411