International projectionist (Jan-Dec 1935)

May 1935 INTERNATIONAL PROJECTIONIST to a sky by night, studded with luminous stars. Likewise, another exhibitor hangs a large Spanish shawl in a prominent position of a space easily darkened. The edges of this shawl are beautifully marked and under ordinary light the center remains blank. In the presence of the ultra-violet, the edges of the shawl take on a luminous irridescent effect of sailboats, waves, and fish. The company monogram of exhibitor, appears brilliantly in the heretofore blank center. Varied Applications Since the effectiveness of these displays depends largely on the maximum brightness contrast between the untreated areas, which remain dark, and the luminous designs, it is extremely essential that visible light be eliminated. A small quantity of stray light is sufficient to illuminate the dark background, thereby reducing this contrast and consequently weakening the effect. With refinements and modifications of present available ultra-violet lighting equipments, and with ultra-violet paints now satisfactorily developed, the art of luminescent effect lighting offers interesting possibilities. Ultra-violet light sources may be concealed in wall urns, indirect floor pedestals, or suspended domes, or in covers, for the purpose of energizing ultra-violet painted scenes or designs in framed pictures, or on the side walls and ceilings. One of the most attractive and intriguing creations is that of a dualscene painted on the upper side walls and ceiling of a night club resort or theatre. With the skill of experienced artists, a simple design is painted on these areas in non-luminous or ordinary paints. A second scene, applied with fluorescent paints, is carefully incorporated in the first design, and combined with these a third view is concealed with phosphorescent paints. Under artificial or natural light, the first design will take prominence. Under the ultra-violet the combination fluorescent and phosphorescent scene will luminously stand out in the dark. On withdrawing the rays, the phosphorescent painted view alone remains visibly luminous. Switches Does the H. L Arc Tail Flame Contribute to Screen Light? DOES the tail flame of a high-intensity arc contribute to screen illumination?, is a question which has served to uncover sharp differences of opinion among projectionists. The Handbook of the National Carbon Co., in discussing this arc, states: "The light from the high-intensity arc . comes from two distinct sources: the crater of the positive carbon and the tail flame. The light from the tail flame represents about 30 per cent of the total light emitted from the arc, but, since it cannot be focussed within the dimensions of the aperture plate and any appreciable portion of it utilized by the optical system, the projectionist is interested only in the crater light . . . "The whiteness and brilliancy of this crater light . . . evidently has its source in something more than the solid tip of incandescent carbon. "This intensified light can be conceived as coming from a portion of the luminous gases of the tail flame, compressed in the crater of the positive carbon by the negative arc stream and thus augmenting the light from the incandescent carbon tip. This explanation may not accord with physical fact, but it aids the imagination in visualizing a reason for the remarkably high intrinsic brilliancy of the high-intensity carbon arc as compared with other sources of illumination. "The fact that the quantity and quality of light from the high-intensity arc, operated at a given current, varies greatly with the manner in which the arc stream From I.P., March, 1934 from the negative carbon impinges upon the flame of the positive, indicates that some condition obtains which is in a measure equivalent to that described." That the answer to this question lies in a clear-cut definition of terms is confirmed in the appended statement by E. R. Geib, manager of the Arc Department of the National Carbon Co.: "The answer to the question — 'Does or does not the tail flame contribute in any way to screen illumination . . .?' is largely dependent on the definition of the term 'tail flame.' The luminous gases of the tail flame emanate from the positive crater of the high-intensity carbon arc. Prior to leaving the crater, these gases may be considered as having been compressed in the crater cup by the force of the negative arc stream, and these compressed gases in the crater cup of the positive carbon are the principal source of light which is in focus with the optical system and, therefore, a source of illumination on the screen. "If the tail flame is defined as com By SIDNEY WEIN THE various switches are among the most important elements of equipment in a projection room. Switches that are faulty in design or manufacture, or that have been worn to an extreme degree, often prove troublesome, and in several instances have been known to stop a show. All projectionists are somewhat vaguely aware of the importance of switches, but very few understand just why a switch burns out. Incidentally, switches are never replaced until they do burn out, thus the responsibility of the projectionist for their care is therefor greater. Arc Switch Burn-Out The arc lamp switch is the one most likely to burn out, the reasons for which being: lugs not clamped tightly enough on the binding posts, wires not soldered properly into the lugs, and excess heat, caused by the wrong size wire or the wrong size switch. Excessive heat takes the temper out of the spring washers on the switch, inducing undue arcing in the hinge part of the switch and inevitably causing the latter to melt. This can happen when the wire or switch is below the proper carrying-capacity for the amperage being used in the arc. This writer recalls one instance of where a 100-ampere switch was used on a certain hi-low lamp, which was replaced with a high-intensity lamp using 130 amperes. Although the projectionists requested the proper size switches at the time the change was made, and have renewed this request many times since, the 100-ampere switches still are in service. The burn-out on this job probably will occur when the theatre is filled with cash customers. Another not infrequent cause of a burnout is the pleasure experienced by some projectionists in seeing the long flash of (Continued en next page) The High-Intensity Arc prising only that portion of this stream of luminous gases coming from the crater of the positive carbon (which lies outside of the conical space defined by the periphery of the condenser lens, or i effecting mirror) and the crater of the positive carbon, it does not contribute at all to screen illumination. "Most of the screen illumination comes from the compressed gases in the crater cup above described, supplemented to a greater or lesser degree by the light from the incandescent carbon within the crater area and that from the luminous gases which have escaped from the crater cup, but are still within the conical space which the optical system is capable of focusing on the aperture plate. "It is in this sense that the statement is made on page 25 of the National Carbon Handbook — ' .... the projectionist is interested only in the crater light.' Considering the tail flame as above defined, there should be no difficulty in interpreting the description of the highintensity arc given in the Handbook."