AT THE HEART OF THE ROAD TRANSPORT INDUSTRY.

Call our Sales Team on 0208 912 2120

A REVOLUTION II

17th January 1936
Page 46
Page 47
Page 48
Page 49
Page 46, 17th January 1936 — A REVOLUTION II
Close
Noticed an error?
If you've noticed an error in this article please click here to report it so we can fix it.

Which of the following most accurately describes the problem?

STREET LIGHTING

MODERN road-traffic conditions demand attention to every improvement which will not only facilitate the, often enormous, flow of vehicles, but which will assist in the promotion of safety. One of• the most important factors in this respect is the adequate lighting of our thoroughfares, and this, at a reasonable cost, so that the

lighting can be extended to include not only the roads in our cities and towns, but, at least, the main routes throughout their length.

Many accidents occur as a result of low visibility. Actually,. street lighting should be of such a quality as will enable objects, both 'near and far, to 'be picked out from the driver's seat, and this without , the need for utilizing powerful headlights, which, whilst being moderately satisfactory to the user personally, constitute a source of danger by dazzling other users of the road.

Until comparatively recently, it may be said that in few cases were the lighting systems for Our roads really satisfactory. Brilliancy could be achieved only at enormous expense.

Some three years ago, the General Electric Co., Ltd., Magnet House, Kingsway, London, W.C.2, developed in its research laboratory at Wembley a new lamp termed the Osira. The main point regarding this product is that, for a given consumption of electrical energy, it affords three times the light as compared with a tungsten-filament gas-filled lamp. Thbs, in one "swoop," improvements were effected which would have been considered impossible in the past. The result is that street lighting in England is going ahead more rapidly than ,in any other country in the world. ' . The light source of this interesting lamp is a column of glowing gas, the electric discharge taking place in mercury vapour and rare gases at a higher pressure

than has ever been used before. Older forms of the mercury-vapour lamp were operated at pressures below atmospheric, whilst in the new type it is slightly above this. This changes the character of the light and gives a much more continuous spectrum.

The actual lamp employed has an inner bulb surrounded by an outer, and there is a vacuum formed between the two, the purposes of this are to retain the heat necessary to vaporize the mercury and to prevent the loss of heat which would result in a diminution of

power. Connected to each lamp is a choke coil in series with it, which limits the current passing to the lamp. In the case of the large units the consumption is 400 wafts.

The long " sausage " column is usually vertical and is quite different from the light source in an ordinary tungsten-filament lamp. Consequently, simultaneously with this production, design had to be concentrated on a new optical system by which the light could be controlled.

The laboratory produced many DOW lanterns in which the control was effected mostly by prisms, by

which the light rays could be diverted to the correct direction. Eventually, a new theory of light effectiveness was developed. The main idea in this is to show objects on the road as silhouettes against a light background. It is not desirable to obtain even illumination, as might be

seen from the air, but even road-brightness, as viewed by the road-user, and in this respect it is the reflection of the road' surface that plays a very important part.

This new principle involved altering the control of the light so that when an object is seen by a driver the background is lighted by the rays from three or four lanterns away. The reflected light from an object close to a lantern is thrown high, and the object may look darker to the driver than another much farther away.

As a result of this success,. more electric-discharge lamps are now used here for street lighting than in the whole of the rest of Europe and America together, and the company concerned is dealing this month with orders for nearly 100 street-miles of lighting.

Adequate and even lighting is particularly essential to long-distance driving, as there is a big and definite strain on the eyes of the driver when he passes through areas with greatly varying systems. Good street lighting can now be effected by these lamps mounted alternately at each side of the road in such a way that,when measured longitudinally, there is not more than 150 ft. between the centre of one lamp on one side and the projected line from the centre of the lamp on the other side.

The difficulty of converting a pencil of light little more than a in. in diameter into wide paths covering a large area of road can readily be understood.

The result of lighting by this means is exactly opposite to that -effected by headlights. On the vehicle, you endeavour to illuminate the object ; on the street, the idea is to obtain a bright surface against which the object can be silhouetted.

At the London offices of the General Electric Co., Ltd., is a demonstration room, in which are exhibited some most interesting models showing the various effects of different methods of street lighting, and one of these, which is shown, in a drawing, clearly indicates how direct downward lighting of a car is not nearly so effective, from the point of view of an approaching driver, as the same vehicle shown against the more-distant street lamps.

The whole object of the new method of lighting is for the lamps to throw long paths of light at a slight angle, which so merge as to give almost even brilliance on the road. It is considered that the best lighting is afforded by unshrouded lamps in the staggered formation already described. Central lighting is not considered to be fully effective, whilst lamps at only one side of the street are unsatisfactory, because they leave the other side in comparative darkness, which causes difficulty to traffic travelling in one direction.

There is a second demonstration machine, which, because of its internal construction, can only be described, not illustrated. The observer looks through eyepieces and sees in front of him a long stretch of road. By turning certain knobs, handles and switches, he can light miniature lamps in practically any desired formation along the centre or sides of the road, and straight or staggered ; bend the road up or down to represent inclines or declivities, and even move it sideways to represent a turn, whilst the whole surface can be turned upside down to present its matt or polished side.

A third model, which we also illustrate, has its miniature lamps equipped with shrouds, which may be dropped to concentrate the light in pools, or raised so that the light is direct. Miniature cars enable various effects to be ascertained.

We have already referred to the Watford lantern, which is primarily intended for fitting to the side of posts, but there are other types constructed on the same principle, known as the Lewisham and the Tunbridge Wells, these being particularly adapted for suspension from their centres by connecting boxes.

Perhaps the most interesting, however, is the new Difractor lantern, which obtained its name from its one-piece refractor, and diffuser globe. In this, the principle of providing beams of light along the road and more diffused light on to the sides is

employed by moulding the one piece of glass into four distinct sections. These are in what may be termed as opposite pairs, the pair for directional beam lighting having the inner surfaces formed into prisms of varying angle, as in the Watford lantern, whilst the other pair has smooth inner surfaces. Externally, however, the whole of the vertical part of the globe is ribbed to give diffusion and prevent glare. In this case there is no opal glass, diffusion being obtained by the ribs or flutes, which are shallow and so do not collect dirt and can easily be cleaned.

It will be realized that the action of the prisms is to give a large number of parallel rays, which is eventually spread by the ribs. •

The bottom of the globe is covered with a number of small cones of specially chosen angles, designed to give suitable downward illumination and a steady increase of intensity at increasing angles to the vertical. It is, of course, essential that such a globe should be fixed in the correct position, and special, provision is made to ensure this ; otherwise its advantages will be lost.

At one time considerable trouble resulted from water percolating through or condensing in the connecting box through which passed the wires conveying the current, the lamps developing sufficient heat to cause the glass to crack when water dripped on to them. The trouble

was cured by designing a new anti-condensation connecting box in which the upper half is blanked off inter

nally, the wires being brought through holes in its walls and then turned up into downward projecting lugs. A study of the drawing will show clearly the arrangement of the device.'

The initial efficiency of a 400-watt lamp of the new Osira type is 18,000 lumens, or 45 lumens per watt, and that of the 250-watt size is 9,000 lumens, whilst the average life is 50 per cent. higher than that of the usual filament lamps.

One of the reasons which inspired the company to develop this special form of lighting was the importance of obtaining contrast. If everything were of the same colour and uniformly bright, the objects could not be distinguished from backgrounds, even by daylight, whilst as the light decreases, contrast rapidly and seriously diminishes ; those lighter objects which, in better light, reflect more than others, Jose this power, so that the eye fails to recognize the differences, despite the fact that it is 10,000 times more sensitive in the dark than in daylight. Thus a headlight seen during the day is hardly noticeable, whereas at night it may be an intense and dazzling beam.

The illustration showing two cats on the road, indicates an attempt to illuminate a light object against a dark background. The cat at the right is grey and reflects some 15 per cent, of the light, and although this is a larger proportion than with most objects, the contrast is bad.

Althougein this article we have dealt particularly with. the subject of Osira lamps and fittings as applied to the lighting of streets, it will be readily understood by our readers that this lamp is of equal value for lighting other large spaces, such as garages, bus stations, etc.

Tags

Locations: London

comments powered by Disqus