along the line of enhancing the value of gas lighting in existing uses and to existing customers, some interesting excursions into new fields have been conducted. A great deal of shop-window lighting has been creditably done. In one city where some efforts has been directed toward developing this use, many of the leading exclusive stores in this city use the incandescent gas lamp for show-window illumination. The greatest obstacle to the use of gas for show-window lighting has been the expense of and the space occupied by the installation, the maintenance of clean glassware and the liability to pilot outage, since in most cases a distributed system requiring a large number of units is preferred. PHOTOGRAPHY Through the development of a mantle of low ceria content having a large energy radiation in the violet end of the spectrum, very creditable studio-lighting has been accomplished. Fig. 24 shows a studio lighting fixture consuming about 100 cu. ft. per hour by which portraits may be taken with shutter-drop (second) exposures on Orthonon plates. Although no effort has been made to exploit this system a considerable commercial demand has spontaneously arisen. The foregoing are indicative of the fact that gas lighting in its most recent development is susceptible of a much more extended and diversified use than it has enjoyed in the past, and waits only upon the expenditure of energy on commercial activity in the less frequently exploited fields. MODERN LIGHTING ACCESSORIES BY W. F. LITTLE The term "accessories" is here used not in its general sense, but rather according to the definition of the Committee on Nomenclature and Standards as employed to designate reflectors, shades, globes and other devices for modifying and controlling the light produced by lamps. The usual functions of such devices are to redirect the light; to diffuse the light; to interrupt the light in certain directions; to modify the hue of the light, or to protect the light source. Accessories in this sense are the tools with which the illuminating engineer works. Since 1910 development in accessories has followed principally the lines of reduced brightness and improved appearance. The increased brightness of light sources has led to the development of accessories which partially or entirely conceal the source. These form in themselves a secondary light source and are capable of decorative treatment to a degree not offered by earlier forms of accessories. Prior to 1910 control of light flux was considered to mean very largely the re-direction of the light as desired. The progress of the past six years lies in the broader definition of control which now is considered to include not only control of the direction of light but also control of brightness and control of color. This extension of the functions of lighting accessories has not involved the abandonment of the most effective and flexible means of controlling direction of light, such as prismatic glass and mirror glass, but has brought about a more subtle and pleasing use of these means in combination with other means for softening and tinting the light. The development of more efficient illuminants in this interim has brought not only the necessity for concealment of sources by lighting accessories, but also the opportunity to apply more effectively the less expensive illumination which they make possible. Accessories development is thus definitely involved with the improvement in light sources, without which such development would probably have been neither essential nor possible. The increased brightness of the lamps, particularly in the smaller sizes, makes some protecting substance advisable. Central station interests, as well as lamp manufacturers, are experimenting with certain bulb coatings which diffuse, and others which both diffuse and tint the light. A demand is beginning to manifest itself for a glass bulb to accomplish this same purpose. Lamp accessories as above described may be made of a variety of materials and of innumerable shapes, and may still fulfil the requirements of the foregoing. The material from which accessories are made may be classified in general as: Metal, enameled metal, glass, fabric, stone and pottery; and the shapes as: Flat, cone, bowl and miscellaneous. From the standpoint of tabulation it is rather unfortunate that so many of the accessories fall in the miscellaneous class. MATERIALS The material should be selected with the proper weighting of the several optical properties of lighting accessories, namely reflection, transmission, and diffusion. Metal.-Metal accessories applied as reflecting media have many advantages, such as durability and rigidity. However, few metal surfaces retain their high reflecting power unless the reflecting surface is protected. A few surfaces, such as polished or matte satin finish aluminum, have been used with some success. Aluminum bronze lacquer on metal is largely used, and has been found very satisfactory, particularly when properly protected from dust and moisture by a transparent coating. Aluminum finished reflectors without a protective surface have been known to depreciate 15 to 20 per cent. within a very short time, and once the surface lustre is gone the reflection coefficient is permanently impaired. The metal reflector with a porcelain or glass enameled surface has more than held its own during recent years for purely utilitarian purposes. The metal gives durability and rigidity and the enamel gives permanency of surface The enamel surface is made so tough that it will withstand much abuse without cracking. Metal reflectors coated with paint, or baked enamel surfaces, make a reasonably satisfactory substitute, where they are not subjected to too much moisture or great changes in temperature. However, the reflecting power deteriorates rapidly and the surface becomes yellow with age. Glass. The best all round material for lighting accessories is glass, which although brittle is beyond question the most permanent available for this purpose. On account of its reflection, transmission and diffusion it is far in the lead. Clear glass, with mirror backing, furnishes a combination of excellent qualities, such as permanency and efficiency. Fabrics. Silks, satins, chintz, etc., are much used for decorative effects where efficiency and permanency are not of importance or where they can be protected against depreciation. Stone.-Marble, alabaster and several other minerals have been used to some extent where richness and distinction are sought. Pottery. Pottery is used where decorative effects and not efficiency are desired. Mirror reflectors are sometimes used in such accessories, thus greatly increasing their efficiency. USES The uses to which lighting accessories are put may be divided into four main classes: (1) utilitarian, (2) utilitarian and semi-decorative, (3) semi-utilitarian and decorative and (4) purely decorative. Utilitarian. The utilitarian accessory may be designated as one whose main functions are efficiency, light control, and in some cases color value, without serious regard to the appearance of the unit. Usually the accessory is a reflector, and in a few cases a shade or globe. Under this classification will be found a wide variation of materials and types such as: Enamel, aluminum, aluminum bronze, white glass, mirror glass and clear glass. Among the most practical is the white enameled steel reflector. Its permanency and durability of surface and practical indestructibility, coupled with its high coefficient of reflection and diffusion, have caused it to be very widely used. Aluminum and aluminum bronze reflectors fulfill most of the functions of the enameled reflector, with slightly better light control, though the permanency of surface even when protected is not so good. White diffusing glass, where protected from breakage, is efficient and durable. Mirror and prismatic reflectors, by reason of their flexibility of light control have a field of usefulness. Clear blue glass units for color matching also fall in this class. Utilitarian and Semi-Decorative. The utilitarian and semi-decorative lighting accessories must be reasonably efficient, accurate in light control, and present an appearance which is unobjectionable. Of this class the majority of accessories are reflectors, a few are bowls, and a few globes, and as a rule these are made of white, clear and mirrored glass. For this purpose the white diffusing glass is perhaps most used, though prismatic and mirrored glass are also employed and in some cases the "crystal roughed inside" globe is still retained. Decorative and Semi-Utilitarian.-In the decorative and semi-utilitarian class the principal functions necessary are, a thoroughly satisfactory appearance and a reasonable degree of efficiency and effectiveness. The effectiveness, must not only be measured by the ratio of output to input, but also in terms of light control and satisfaction. Light control in this connection is not necessarily light redirection, but is the securing of the proper balance or weighting of reflection, transmission, and diffusion. This class embraces the reflector, the transparent, translucent and opaque bowl, and the transparent and translucent globe. It is therefore essential that a wide range in these qualities be available. The materials from which these are usually made are: white, clear and mirrored glass, tinted or colored glass and fabrics. In this class may be placed the white diffusing glass where transmission and diffusion are important; the prismatic and mirrored glass where control and efficiency are important; tinted or colored glass, and fabrics where colored light and decorations are required. Decorative. The decorative accessory may be of such varied construction, design or material that it may include anything from the bare light source to the most inefficient and highly absorbing media. It includes the reflector, the shade, the bowl, the globe and other forms which cannot be classified. In many cases the decorative feature is all-important and the illuminating value is a secondary consideration. The materials from which these accessories are made are: white, tinted or colored glass, iridescent and art glass, fabrics, stone and pottery. The white glass, tinted with a superficial coating of enamel, paint, or iridescent glass, is much used. This superficial coating may be etched away, making innumerable possibilities for ornamentation; or the white glass may be employed in its usual form with the walls of the accessory varied in thickness, in order to bring out the decoration in relief. The use of colored glass, iridescent glass, art glass, fabrics and pottery is extensive in this type of accessory, and glass has supplanted to a considerable extent the metal work formerly utilized. STRUCTURAL CHARACTERISTICS The glass used for lighting accessories may be divided into four structural types: Clear glass, opal glass, cased glass and suspension glass. The clear or crystal glass is used in the manufacture of prism, |