Illuminating Engineering

ILLUMINATING ENGINEERING, term now used to denote all applications of natural and artificial light in the service of mankind. Progress in Great Britain since 1910 is largely the result of the formation (in I 909) of the Illuminating Engineer ing Society, in which makers of lamps and lighting appliances and users of light co-operate; all illuminants are represented and all aspects of the subject, economic, hygienic and artistic are consid ered. A similar body, the pioneer in this field, has been in existence in the United States since 1906, and corresponding bodies have been formed in Germany 0913), Austria and Hungary (1925), Japan (1915) and Holland (1926). In Germany two additional societies operating in Karlsruhe and in the Rhine-Westphalia dis trict have also been created. Attention has been paid to illumina tion at many international congresses, thus promoting the ex change of views between experts in different countries. The re organization of the International Photometric Commission, founded in 1900, as the International Illumination Commission was stopped by the World War, but a fresh start was made in 1921, and the leading countries are now represented with national committees for the respective countries. (See J. W. T. Walsh, "International Co-ordination in Illumination," Trans. First World Power Congress [1924], vol. 3.) Much has been done towards standardization and agreement on common principles. Definitions of the main photometric quantities have been adopted, and a more extended series of definitions, symbols, etc., framed, while sub-committees to deal with lighting legislation, automobile head lights, etc., have been formed. At the sessions held in Geneva in 1924 and at Bellagio in 1925 further activities were initiated and the commission is extending its work to deal with various practi cal problems. Evidence of further progress in this direction was afforded at the International Illumination Congress held in the United States in 1928.

The International Candle.

A noteworthy step, dating from 1909, has been the agreement between France, the United States and Great Britain and, recently, also Russia, on an international candle so that the same unit of light is now in use in all four countries ; but in Germany and some other countries the Hefner candle (equal to 0•9 international candle) is still in use. Preser vation of the unit of light is now effected by the exchange of specially prepared electric lamp-standards between the official laboratories in the countries concerned. Meantime experiments are being made with a view to evolving an absolute standard of light, e.g., one based on the maintenance of a "black body" at a specified temperature.

Progress in illumination has kept pace with this advance on the scientific side. Electric lamps, filament and arc, have been developed (see ELECTRIC LIGHTING). In the field of gas lighting there has been steady progress in design, one instance being the smaller and more compact forms of high-pressure gas lamps, now rated to give 6o candles per cu.ft. of gas consumed. In low pressure gas lighting the use of superheated clusters of inverted mantles has made possible a gain in efficiency estimated at 3o%. The distribution of the light from a number of smaller mantles is considered an advantage, and the smaller types of mantles are the most durable. Cluster-lamps giving up to are now available.

Theory of Radiation.

Researches into the theory of radia tion and the principles underlying illuminants provide a clearer understanding of the luminous efficiency theoretically obtain able. Thus a light source yielding visible white light and no non-luminous vibrations would operate at approximately 26c.p. per watt, whilst if the light were confined to the most efficient yellow-green section of the spectrum as much as 6oc.p. per watt might be obtained. But in the case of new illuminants efficiency is not the only consideration; such special qualities as the colour of the light (as in the neon lamps) or the nature of the supplementary invisible radiation (as in the quartz tube mercury vapour lamps) may be of even greater importance.

Reflectors, etc.

The design of shades, globes and reflectors for use with lamps has assumed great importance. By suitable design of a reflector the distribution of light from a source may be altered within wide limits. Thus extensive, intensive and focusing forms of reflectors yielding standard curves of light distribution have been designed, and corresponding rules for height and spac ing, designed to give even illumination on the working plane have been derived. In most cases a shade or reflector is designed to direct most of the light downwards, where it is chiefly needed. But other cases occur, for example in shop window lighting and the illumination of large posters, etc., where reflectors are so designed and spaced as to yield an illumination over an extensive vertical area. Another function of shades and reflectors is to screen the actual source of light from the eye. Even when only vacuum metal filament electric lamps were available the glare from exposed filaments irritated the eye and prevented it from registering the full effect of the illumination provided. In the case of the gas-filled lamps, with their very much brighter filaments, the need for. scientific screening is yet more evident. Hence in the leading stores concealed lighting of show-windows, with the light thrown on the goods but the sources concealed from the eyes of observers, is coming to be regarded as the correct method; and it is only in the smaller shops that exposed sources of light are still too frequent. A special instance of a concentrating reflector is to be found in the "floodlighting" units, consisting of an incan descent lamp with a special "bunched" filament at the focus of a parabolic mirror. Such units are miniature searchlights and are now being used to illuminate the facades of buildings. The design and application of such units have been dealt with fully in a paper recently read before the Illuminating Engineering Society by W. J. Jones.' With the searchlight proper, using an arc, the dimensions of the source of light can be much reduced and a beam of many millions of candle power attained.

Searchlights.

A notable advance during the World War was the design of searchlights using cooled electrodes leading to a yet smaller and more brilliant source and corresponding greater concentration. The cooling has been effected by two dis tinct methods, a blast of air and a spray of alcohol ; in both cases a very substantial increase in beam-candle power for a given current consumption was obtained.' The brightness of the crater in such cases has been estimated at 200,000-300,000 candles per sq.in., as compared with 85,000c.p. per sq.in., in the case of the ordinary searchlight. In Germany, Lummer, working with an arc operating in a chamber under an air-pressure of 2 2 atmos pheres, is said to have attained the enormous brightness of 1,500 00o candles per sq.in. But this method has apparently not yet reached a practical An apparatus capable of projecting pure spectrum colours on the stage, which is in effect a giant spectroscope, has been de signed. By the Mutochrome a series of superimposed patterns can be projected on the screen and the colour of each varied at will. This is likely to prove of considerable value to designers of wallpapers and coloured fabrics, as well as having a possible application for the projection of luminous scenery on the stage.

Artificial Daylight.

Efforts have also been made to provide "artificial daylight," i.e., to correct the light from artificial illu minants and render it equivalent to normal daylight for the matching of colours. Two methods of effecting this correction have been applied. In the Sheringham unit the light from a gas filled lamp is reflected from an upper surface coated with a pat tern of green, blue and a small amount of yellow in suitable pro portions. In the system usually associated with the name of F. E. Lamplough the light is filtered through a combination of tinted glass. In either case the efficiency of the apparatus is necessarily low, 6o% or more of the original light being lost in making the correction. But the advantage to firms in the dyeing industry and others concerned with delicate colour-matching of having an invariable artificial light, independent of the wide variations of natural daylight, is very considerable. Attention has also been devoted to the production of fittings yielding light visually similar to average daylight, but less completely corrected. Such light ing units which have a relatively high luminous efficiency are recommended for use in picture galleries, shops devoted to 'Ilium. Eng. (Jan. 1927) .

Sperry Searchlight,

" Electrician (Feb. 2, 1917) ; Haydn T. Harrison, Illum. Eng. (March 1918) .

Bloch

, Lichttechnik (1921) . Eng. (May 1925) coloured objects, etc., and in cases where daylight requires fre quently to be supplemented by artificial light. It is suggested that such light is less fatiguing to the eyes than entirely uncor rected artificial light.

The psychological and other problems attending the lighting of streets, schools, factories, shops, etc. and the avoidance of eye strain in cinemas, the importance assigned to proper lighting in factories, and the interests of health, safety and efficiency of work have been investigated by the Illuminating Engineering So ciety and Home Office committees.' Evidence on lighting require ments in factories has been collected from many different sources, and records of over 4,00o tests of illumination in different fac tories have been presented. The minimum values of illumination in the interests of safety (o. 2 5–o•4f t.c.) are established. Recom mendations on the subject of avoidance of glare, flickers and in convenient shadows have been made, and the illumination required for carrying out work is demonstrated to be not less than three foot-candles for fine work and five foot-candles for very fine work. Consultations with various joint industrial councils are now proceeding with a view to determining what constitutes suitable and adequate lighting for processes in their respective industries.

In the United States detailed codes of industrial lighting have been adopted in various States. In principle these follow closely the recommendations of the British committee. Methods of grad ing various lighting units according to the degree of "glare" are outlined, and the positions which may safely be assigned to such units in a workshop are tabulated. The codes also contain stan dards of the illumination requisite for various processes, a dis tinction being drawn in the most recent codes between the mini mum value desirable and higher values recommended in the in terests of economic production. A considerable amount of re search has been devoted to the relation between conditions of illumination and efficiency of work. Thus it has been shown by Dr. Ives of the United States public health service that the despatching service in post offices was expedited and rendered more accurate by better conditions of illumination tests in lab oratories in Germany have likewise revealed a close connection between illumination and many processes involving exact vision and manual dexterity.' The subject of industrial lighting has likewise been studied by the International Labour Bureau of the League of Nations in Geneva.

Particularly difficult cases of industrial lighting also form the subject of study by the committee on illumination, working under the Department for Scientific and Industrial Research, on which eminent architects and medical men, besides lighting experts, are represented. It has published several informative reports, amongst which that dealing with the lighting of printing works has ex cited special interest. In this enquiry the important conclusion was reached that full efficiency in type-setting by band is attained only with an illumination of the order of 20-25 This committee also deals with all enquiries bearing on illumina tion received from the various Government departments. In con nection with this and other aspects of lighting, increased atten tion is now being devoted to the hygienic side, and at the Inter national Congress for the study of industrial hygiene held in Geneva in 1924 a special resolution was passed accepting good illumination as of equal importance with heating, ventilation and sanitary conditions in the interests of health and safety.

Standardization.—Standardization in various fields is being dealt with by various sub-committees, working under the British Engineering Standards Association, which have prepared speci fications on the performance and dimensions of electric lamps, and have also issued standard specifications for portable illumina 'Reports of Departmental (Home Office) Committee on Lighting in Factories and Workshops, First Report, Cmd. 8,000, vol. i and 2 (1915) ; Second Report, Cmd. 1418 (1921) ; Third Report, Cmd. i686 (1922).

'Ilium. Eng. (April 1925) .

'The Relation between Illumination and Efficiency in Fine Work (Type-setting by Hand) ; Joint Report issued by the Industrial Fatigue Research Board and the Illumination Research Committee (1926).

tion photometers,' reflectors used for industrial lighting,' street lighting' and illuminating Traffic and Lighting.—Experience during recent years has shown that the questions of lighting and transport are closely related. With the progressive increase in the volume of f ast driven motor traffic the necessity for good public lighting has become even more urgent than in the past ; and the increase in the number of street accidents year by year has drawn public attention to the importance of the question. A new problem is presented by the lighting of arterial roads connecting cities. These routes are primarily intended for fast motor traffic and their utility will not be realized fully unless adequate artificial lighting is provided, enabling them to be used with safety by night as well as by day. Special methods of illuminating such routes are now the subject of consideration. Light is being used to an ever increasing extent as an aid to the guidance of traffic and, on the initiative of the Association of Public Lighting Engineers a resolution was recently passed advocating standardization of traffic signs and signals.' Many devices eliminating glare from powerful automobile headlights have been suggested, some of the most promising based on the limitation of the main portion of the beam below a certain horizontal plane so as to avoid the direction of rays into the eyes of approaching drivers or pedestrians. But the most hopeful solution lies in the provision of better public lighting, which would render very powerful headlights unnecessary. Prog ress in these various directions has been aided very greatly by the introduction of simple forms of instruments for measuring illumination of which quite a variety of types is now available. The information acquired in this way has been very helpful in framing recommendations for the degree of illumination neces sary for various purposes.

BIBLIOGRAPHY.-A. P. Trotter, Illumination, its Distribution and Bibliography.-A. P. Trotter, Illumination, its Distribution and Measurement (191 I) ; L. Gaster and J. S. Dow, Modern Illuminants and Illuminating Engineering (192o) ; M. Luckiesh, Artificial Light, its Influence on Civilisation (1921) ; Lichttechnik, ed. by Dr. L. Bloch and issued by the German Illuminating Engineering Society (Munich, 1921) ; J. W. T. Walsh, Elementary Principles of Lighting and Photometry (1923) ; see also The Illuminating Engineer (The Journal of Good Lighting), official organ of the Illuminating Engineering Society ; The Transactions of the Illuminating Engineering Society in the United States; and Licht and Lampe (official organ of the Illuminating Engineering Society in Germany) . (L. GA.)