International projectionist (Oct 1931-Sept 1933)

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PROGRAM EMBELLISHMENT WITH ULTRAVIOLET EFFECTS Alexander Strobl* and Robert L. Zahour^* MORE than three hundred years ago, the Italian scientist Balmain discovered the photochemical property of certain substances to absorb energy from visible light sources, and produce in themselves a luminous glow when observed in the dark. Further study of light sources, capable of energizing these substances, revealed that the longer wave-lengths of the ultraviolet invisible radiations (3,200 A to 4,200 A) are transformed by certain substances into longer waves of a length found in the visible spectrum. This phenomenal transformation varies in different materials, making ' available a variety of luminous colors. Pigments extracted from these substances are commonly called "ultraviolet paints", and because of their ability to glow they are said to be "luminescent" when exposed to the ultraviolet radiations. Two kinds of paints have been discovered for producing practical luminous effects — namely, fluorescent and phosphorescent. Fluorescent pigments are those which become luminous when subjected to ultraviolet radiations. These paints are available in nearly all colors of the rainbow. Phosphorescent paints will emit a self-luminous glow for some period after the ultraviolet has been withdrawn. This latter kind of paint is 'Stroblite Company, New York City. **Westinghous3 Lamp Co., Bloomfield, N. J. ROUGH REFLECTOB METHOa OF WIRING 'black BULb' ULTRA VIOLET LAMPS FIGURE 1 Various methods of wiring S-anip., 15-volt "Black Bulb" ultraviolet lamps on 110-120 volt A.C. circuits Ultraviolet radiation long has been used as an aid in theatre effect ivork, although only on a limited scale by means of the carbon arc and almost exclusively in connection with stage presentation workThe accompanying paper, a contribution to the Illuminating Engineering Society, describes a new "black bulb" mercury vapor lamp development which, combining efficiency with simplicity of operation, promises to open up many new applications of ultraviolet radiation effect work in the theatre — not only for stage work, but also in connection ivith motion picture presentations.— Editor. available in several colors. The phenomenal glowing characteristics of each of these two types of paints permit one to obtain two distinctly different luminous effects when used jointly in a single composite design. Ultraviolet Equipments Since most of the early uses of ultraviolet paints were confined to stage effects, the arc spotlight, equipped with suitable glass filters to screen out practically all of the visible light, was used satisfactorily to project invisible ultraviolet radiations on to the specially treated scenes and costumes. Because of the abundance of ultraviolet generated, the arc projector still is employed for this purpose and particularly where coverage of large production scenes at long beam throws is necessary. An outgrowth of the stage effects brought about uses for ultraviolet paints in advertising posters, small dual-scene paintings, and in miniature design novelties. For these applications, light-tight projectors equipped with dense blue heat-resisting glass filters and ordinary high-wattage Mazda lamps, were found more convenient than arc units. However, due to the proportionately small amount of ultraviolet liberated by Mazda lamps compared with visible light, [11] only medium-density filters can be used for screening out the visible radiations. For some applications, the small percentage of visible light which escapes from these modified equipments is 'objectionable, while in other cases, if fs an asset. Continued growth in the application of ultraviolet' effects has led to the development of dense blue grass mercury vapor' tube^, 'and finally, the "black bulb" mercury vapor lamps. Since the visible light from these sources consists of chiefly blue-green mercury spectrum lines, the thickness of the dense blue filter glass in the tube of "black bulb" is not as great as in the screens employed for masking carbon arcs or high-wattage Mazda lamps. Consequently, more ultraviolet is transmitted for useful jDurposes. The mercury vapor tube and its accessories for operation is essentially the same as the standard CooperHewitt lamp, except that the tube is made of a dense blue ultraviolet filter glass. "Black Bulb" Mercury Lamps The "black bulb" ultraviolet lamp is similar to the ultraviolet health lamp in construction details and operating characteristics, but is provided with a special dense purple glass bulb which absorbs practically all of the visible light, yet transmits a high percentage of the ultraviolet. In Figure 1 is shown various methods of wiring the 5-ampere, 15-volt "black bulb" ultraviolet lamps of sources of 110-120 volts A.C. Since the lamps operate at 15 volts, they must be burned in series with a 5-ampere reactor when connected to the 115-120 volt A.C. supply. This combination consumes approximately 100 watts. The reactor can be adjusted to operate two or three lamps if desired. A convenient scheme in trough arrangements is to mount incandescent lamps between the black bulb lamps, thereby permitting each circuit to be operated alternatingly through a flasher. In making their debut upon the