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1950-51 Theatre Catalog, 9th Edition, Page 342 (320)

1950-51 Theatre Catalog, 9th Edition
1950-51 Theatre Catalog
1950-51 Theatre Catalog, 9th Edition, Page 342
Page 342

1950-51 Theatre Catalog, 9th Edition, Page 342

completely by lamps using "Suprex" carbons, which, due to carbon and optical system developments, surpassed them in light output with substantially lower operating costs.

However, during the past two or three years, improved carbons and optical systems have made it possible to bring out new high-intensity, rotating-carbon reflector lamps which surpass the output of the old non-rotating lamps using "Suprex" carbons. The new lamps employ 9 to 10mm plain positive carbons with copper-coated "Orotipli negative carbons placed at an angle below the horizontal. The positive carbon is rotated during burning to preserve a symmetrical crater.

Some of these lamps are equipped with automatic focus control devices and means for automatic arc regulation. A heat-responsive, bi-metallic strip device is employed to position the positive crater automatically at the focal position of the reflector. Other means are used to control the position of the negative carbon with respect to the positive to maintain proper are burning conditions. These lamps also employ redectors of a higher optical speed than those available previously and are capable of effectively utilizing projection lenses in the range of speeds from F/l.9 to F/2.0.

Some of these lamps employ watercooling for the positive contacts, while others use forced air currents in various fashions. According to Table 1, these lamps are capable of lighting screens of 25 to 30-foot width to maximum recom.mended brightness and 30 to 35 feet to the minimum recommendation.

. Rotating Condenser Lamps

This type of lamp represented the earliest application of the high-intensity arc to motion picture projection and first appeared approximately 30 years ago. However, improvements in carbons and optical systems have kept this system in the forefront, so that it continues to furnish the projection for most of the large indoor theatres and a sizeable percentage of the drive-ins today.

These lamps employ positive carbons 13.6mm in diameter with copper-coated nOrotip" negative carbons placed at an angle, as shown in Figs. 2 and 4. The positive carbon is rotated during burns ing to preserve a symmetrical crater form. The so-called liregular" carbon is operated at 125 to 150 amperes, while the fintexll Super is rated at 170 to 180 amperes. The firegular" can light screens of 25 to 30-foot widths to maximum levels and 30 to 35 feet to minimum recommended levels. The fintex" Super is capable of increasing. these widths approximately 10%.


Light-Absorbing Devices

It should be kept in mind that the screen widths indicated in Table I are applicable in cases where there are no filters or other light-absorbing devices in the beam. In cases where such accessories are present, correction of the figures in Table I is necessary. For example, in some cases a draft glass is used in the projector, and, in others, a port glass is used on the booth, If these are present, it will be necessary to allow for their light losses. Then, all of the

FIGURE G-An even balance of all colors assures

a snow white light of daytime quality.

rotating high-intensity systems, both redector and condenser, may require protection from heat on the film. If this shielding is accomplished by a heatabsorbing glass, its light los5es must be included. For example, a light loss of approximately 20% will reduce the corresponding screen widths in Table I by about 10%.

Reserve Capacity Allowance

It should further be remembered that the values in Table I pertain to highquality equipment in good condition and accurately aligned. Since optical systems show some deterioration with age, some allowance should be made to take account of the fact that it will not be possible to maintain top values in all cases at all times. Therefore, the wise purchaser will make allowance for some reserve to compensate for those losses and to provide for exceptional instances, such as dark prints with which it may be desirable to increase the light output of the lamp. If one wants to maintain the brightness constantly above the recommended minimum, then the lamp should probably be chosen with an inherent capability of providing at least the maximum recommended brightness, and, in cases where there are other known losses, the purchaser may even wish to provide more reserve capacity.

On this basis, that is, choosing a system capable of providing at least maximum recommended brightness, we can make a rough breakdown of the fields of application of the various lamps as follows. One could employ the ffOneKilowatt" lamps for screens up to approximately 17 feet and the HSuprex" carbon reflector lamps in the range 18 to 27 feet. A rotating-carbon type lamp then would be necessary for screens larger than 27 feet in width. This may

FIGURE 4-Diagrams oI high intensity are lamp: (above) condenser type: (below) reflector type.

often be capable of illuminating screens as large as 30 to 33 feet. If heat protection devices reduce the light by 10 to 20%, however, the rotating type lamps may not adequately illuminate screens larger than 27 to 30 feet in width.

No Drive-In Standards Yet

All of the above correlation of projection systems and screen widths has been based on the recommended standards of brightness for indoor theatres. There are no recognized standards of brightness for outdoor theatres at this time. As shown in Table I and Fig. 1, it is impossible with existing projection systems to light screens in the 50 to 70foot class, widely used in drive-in theatres, to even the minimum recommended brightness for indoor theatres. This does not mean that outdoor theatres cannot be successfully lighted with existing pros jection systems. There may be compensating factors, such as a larger viewing angle and absence of house illumination, which may facilitate the use of lower brightness levels in outdoor theatres.

However, there is no little doubt that these outdoor screens need all the light that they can get from present systems and could advantageously employ considerably more than they are using at present. However, in the absence of more powerful systems and until still further improvements in this line are forthcoming, outdoor theatres should unquestionably use the most powerful projection systems possible.


The theatre owner of today, whether indoor or outdoor, has a wide variety of high-intensity lamps from which to choose, all designed to give a large volume of snow-white light at a very reasonable cost. SurVeys before World War II showed that the cost of projection light amounted to only a little over 2% of the total operating cost of the theatre. The small increase in the cost of carbons and power in relation to the much greater increases that have taken place in the other expenses of a theatre make the present day cost of projection light an even smaller fraction of the total than preewar. Surely, in View of the importance of projection light to the quality of the picture and the satisfaction of the theatre patron and the very minor status of projection light cost, the first consideration of the theatre owner should be to obtain the best projection light possible.

It is hoped that the data here presented will be helpful in the selection of suitable projection lamp equipment and will indirectly assist in raising the standard of projection light throughout the country.


We are particularly proud at any lime to present the views of Messrs. Lozier und Geib, [or they are recognized us authorities in the field of projection light sources. Their current analysis however is particularly timely. Great strides have been made in. this field in recent years and every theatre

cxorulire should read the. foregoing. ## THEATRE CATALOG 1950-51
1950-51 Theatre Catalog, 9th Edition, Page 342