Annual Conference at Eastbourne
September 13th-17th, 1948

There will be an indoor exhibition of street lighting apparatus and equipment where leading manufacturers will be displaying modern equipment. The Exhibition Hall will be the Winter Garden next to the Conference Hall.

The indoor Exhibition of Street Lighting apparatus and equipment is being staged in the same building as the Conference Hall. The APLE with the co-operation of the Eastbourne Authorities have permission to use an area of ground immediately adjointing the Conference Hall where lamp columns will be erected.

Eastbourne's lighting engineer, Mr. N. Boydell, added a history of Eastbourne's street lighting.

There was an extremely comprehensive display of equipment in the same building as the Conference Hall. On the rink adjoining the Conference Hall there were 60 lamp columns which proved of great interest, as did the ladders and tower wagons, also on show. It should be noted that this phase of the Conference is proving itself a great attraction and more and more manufacturers expres their desire to participate in the exhibition. - [Public Lighting #51]

From left to right: The Mayor of Eastbourne, President Mr. N. Boydell and Vice-President Mr. A. S. Tapsfield opening the Exhibition by the Siemens and ELECO stands.

Additional information about the Conference is lost as Public Lighting Issues #52 and #53 are missing from the archive.

Planned exhibitors were: British Sangamo Co. Ltd., Concrete Utilities Ltd., Gowshall Ltd., Philips Electrical Ltd., Engineering And Lighting Equipment Co., Ltd., Siemens Electric Lamps And Supplies Ltd., REVO Electric Co., Ltd., The Electric Street Lighting Apparatus Co., William Edgar & Son Ltd., The Brighton Lighting And Electrical Engineering Company, Ltd., Metropolitan Vickers Electrical Co., Ltd., The Horstmann Gear Co., Ltd., Metropolitan Gas Meters Ltd., Willey And Co., Ltd., Poles Ltd., Venner Time Switches Ltd., Holophane Ltd., The General Electric Co., Ltd., Simplex Electrical Co., Ltd., British Electrical Development Association, Ford Motor Co. Ltd., William Sugg And Co., Ltd., Parkinson & Cowan (Gas Meters) Ltd., Automatic Telephone And Electric Company Limited, British Gas Council, The British Thomson-Houston Co., Ltd., Broads Manufacturing Co., Ltd., Stanton Ironworks Co., Ltd. Spun Concrete Ltd., Thorn Electrical Industries, Ltd., Measurement Ltd., Shaftesbury Ladders Ltd., Vauxhall Motors Ltd., Stewarts And Lloyds, Ltd. and Cable Covers Ltd.

Abstract: Descriptions of lanterns and equipment displayed by: Sangamo Weston, Ltd. (1), Concrete Utilities Ltd. (2), Gowshall Ltd. (3), John Gibson & Son, Ltd., Philips Electrical Ltd. (6), Engineering And Lighting Equipment Co., Ltd. (7), Standard Telephones and Cables, Ltd., Siemens Electric Lamps And Supplies Ltd. (8), REVO Electric Co., Ltd. (10), Stewarts And Lloyds, Ltd. (11), The Electric Street Lighting Apparatus Co. (12), Automatic Light Controlling Co. Ltd. (13), The Brighton Lighting And Electrical Engineering Company, Ltd. (14), William Edgar & Son Ltd. (15), Metropolitan Vickers Electrical Co., Ltd. (16), Horstmann Gear Co., Ltd. (17), Metropolitan Gas Meters Ltd. (18), Willey And Co., Ltd. (19), Evered And Co., Ltd., Poles Ltd (20), Horstmann Gear Co., Ltd. (21), Cable Covers Ltd. (22), Venner Time Switches Ltd. (23), Holophane, Limited (24), The General Electric Co., Ltd (25), Simplex Electrical Co., Ltd. (26), British Electrical Development Association (27), Ford Motor Co. Ltd. (28), William Sugg And Co., Ltd. (29), Parkinson & Cowan (Gas Meters) Ltd. (30), Automatic Telephone And Electric Company Limited (31), British Gas Council (32), The British Thomson-Houston Co. Ltd. (34), Fulford Brown Brothers (1939) Ltd. (35), Thorn Electrical Industries Ltd. (37), Shaftesbury Ladders Ltd. (40), Stanton Ironworks Co., Ltd. (41), Broad & Co. Ltd. (43), Spun Concrete Ltd. (45), Sordoviso Switchgear Ltd. (46), Aspec (London) Ltd., Vauxhall Motors Ltd. and The Royal Society for the Prevention of Accidents.

Adverts: Poles Ltd, Concrete Utilities Ltd., Gowshalls Ltd., John Gibson & Son, Ltd., Engineering And Lighting Equipment Co., Ltd., Standard Telephones and Cables, Ltd., Siemens Electric Lamps And Supplies Ltd., REVO Electric Co., Ltd., Stewarts And Lloyds, Ltd., The Electric Street Lighting Apparatus Co., Automatic Light Controlling Co. Ltd., The Brighton Lighting And Electrical Engineering Company, Ltd., William Edgar & Son Ltd., Metropolitan Vickers Electrical Co., Ltd., The Horstmann Gear Co., Ltd., Metropolitan Gas Meters Ltd., Willey And Co., Ltd., Philips Electrical Ltd., Poles Ltd, Poles Ltd, Evered & Co. Ltd., The Horstmann Gear Co., Ltd., Cable Covers Ltd., Venner Time Switches Ltd., Holophane, Ltd., The General Electric Co., Ltd, Simplex Electrical Co., Ltd., British Electrical Development Association, Ford Motor Co. Ltd., Measurement Ltd., William Sugg And Co., Ltd., Parkinson & Cowan (Gas Meters) Ltd., British Gas Council, The British Thomson-Houston Co. Ltd., Fulford Brown Brothers (1939) Ltd., Automatic Telephone And Electric Company Limited, Thorn Electrical Industries Ltd., Shaftesbury Ladders Ltd., J. E. Wildbore, Stanton Ironworks Co., Ltd., Broads Manufacturing Co., Ltd., Foster And Pullen Ltd., Spun Concrete Ltd., Sordoviso Switchgear Ltd., Aspec (London) Ltd., Vauxhall Motors Ltd., The Royal Society for the Prevention of Accidents, Londex Ltd., C. H. Kempton & Co. Ltd. and The General Electric Co., Ltd.

Provisional papers (as planned in Public Lighting #50):

Presidential Address by N. Boydell, M.I.E.E., A.M.I.Mech.E.

Unidirection Lighting of Dual Carriageways and Side Roads by J. S. Smyth, B.Sc.(Eng), A.M.I.E.E., (GEC)

Street Lighting in the Vicinity of Aerodromes by S. English, D.Sc., M.I.E.E., F.Inst.P (Holophane) and J. G. Holmes, B.Sc., A.R.C.S., F.Inst.P., F.I.E.S.

Basic Principles in the Design of a Street Lighting Installation and Their Practical Application by David M. Thompson, A.M.Inst.Gas.E., F.I.E.S. (Wigan)

One Hundred Years of Research and Development in Electrical Light by J. N. Aldington, B.Sc., Ph.D., F.R.I.C., F.Inst.P, F.I.E.S. (Siemens)

Safety First on the Highways - With Special Reference To Street Lighting by Charles M. Melton (Dagenham)

N. Boydell, M.I.E.E., A.M.I.Mech.E.
(Manager, East Sussex and South-West Kent South-Eastern Electricity Board)

Keywords: APLE: Conference, Lighting: Future, Lighting: History, Lighting: Legal, Lighting: Statistics

Tuesday, September 14th, 1948

A copy of the paper was included with: Public Lighting, Vol. 13, No. 51. July-September 1948.

Abstract: A view of the work of the APLE. This includes a brief review of the main aspects of public illumination which has concerned the Association in the past, concern it now and concerns it in the future.

Public lighting in 1924 was very haphazard and there was no independent body from whom authorities could gain information. Since those days, the Association has been recognised by Government Departments, Town and City Councils, and has rapidly increased its membership and continues to do so.

Sodium and mercury lamps have been applied to street lighting and it was at this point that the public suddenly became street lighting conscious.

The progress of the Association is in proportion to the development of street lighting. Recently two local centres have been formed, one in Lancashire and one in Scotland.

The Association, during its growth, has held Conferences in many towns, usually with an indoor exhibition of equipment alternating each year with one out of doors. The value of these Conferences lies not only in the Papers delivered and the subsequent discussions, but also in the opportunity for interchange of views and information.

The chief function of the Association is to educate the public in general, and the lighting authorities in particular, with regard to the necessity and value of good lighting. That there is an appalling lack of uniformity in street lighting throughout this country is undeniable; lack of uniformity in standards, arrangements, spacing of columns, heighs of columns and examples of completely different systems with different standards of illumination on each side of the same road. Differences in lighting is not lack of money, but lack of education or indifference on the part of the authority.

The fundamental trouble with bad lighting is that the provision of lighting is still optional by local authorities; and there are so many lighting authorities who, because of their limited size, have not had and never will have, sufficient money to provide lighting up to the standard needed today.

There have been half-hearted attempts to meet this position such as the provisions of the Road Traffic Act, 1934, giving County Councils certain powers (of which little advantage has been taken), and those of the Trunk Roads Act, 1936, which allows the Ministry of Transport to assist financially with the lighting of trunk roads. This has been excerised considerably, but at best it is merely a scratching of the surface. The MOT's Final Report recommends that administration be put in the hands of fewer and large units, but there's no reason why each local lighting authroity should not continue to administer its own lighting, provided it is made a legal obligation and is sibject to some central control and improvements are substantially helped by national grants.

The volume of present-day traffic approaches twice that of pre-war, but the majority of the roads remain lighted to the pre-war standard (ignoring the 25% fuel cut). This traffic demands better lighting. The use of headlights in poorly, lighted areas, instead of lessening the lighting risk, contributes to it. Properly lighted roads induce drivers to switch off their headlights.

In 1938 there were 740 fatal accidents in factories and 6,642 fatal accidents on roads, and of the latter, for every one which occurred in daylight, three occured at night.

With regard to the relation of street lighting to crime, there are statistics available from America which clearly prove that good street lighting reduces that type of crime of which 90% takes place after dark. Our own Chief Constables' Association has said that effective lighting acts as a deterrent to criminals.

The Association can point to hundreds of miles of well-lighted motoring roads, shopping streets and side roads, and even in these cases, many of the advantages of such lighting have still to be appreciated. The enlightened authority primarily looks upon it good lighting as being for the convenience and safety of the road users, and also for the prevention of crime and other Police purposes, yet there are other reasons for lighting a town well. For instance, for the convenience of citizens as they go their lawful ways and also to incrase the attractiveness of shopping centres and civic centres - in general, to give a town as pleasing an appearance by night as possible. All these aspects have a real economic value.

Good lighting is often the reason for, and an indication of, civic pride. It is often an indication of prosperity, and in the long run the value of property is increased. Streets which were lighted for years in a most dismal manner are now lighted exceeding well and, by day, the well-designed columns enhance the appearance of a street. Frequently, in front of the town hall, the old cast iron columns and enamel reflectors have been replaced by dignified and properly designed columns with appropriately impressive fittings. We still have a long way to go in the coutnry with regard to appreciation of the daylight appearance, although the importance of this is now realised and the Royal Fine Art Commission are actively interested. The USA are very far ahead of us in this direction, and in Paris they really are concerned with aesthetic values. (On the Pont du Carrousel, there are columns which, by daylight, are only 14 meters high so as not to spoil the aestheic views but by automatic means, at dusk the columns are extended, telescopic fashion, until they are 21 meters high, to provide appropriate light distribution, the whole process being reversed at dawn). Ideas like this could well be applied in this country to the new Waterloo Bridge in London.

There needs to be maximum co-operation between Lighting Engineers and Town Planners and others responsible for the planning, construction and maintenance of roads. One example is the growing interference with good lighting by trees planted along the highway. The other example is the road surface - there is a need for the road surfaces to be of light matt colour to provide effective reflection and diffusion of light. This presents a difficult problem since hte Road Engineer considers his surface from a different point of view and is not concerned with colour and reflectivity. The Association has been very much concerned about this aspect.

Lighting authorities, large and small, cannot afford not to be advised by someone really competent to deal with the subject and cover the following:

• Schemes in line with modern requirements.
• Advice on the replacement of antiquated fittings.
• Comparision of manufacturers' proposals and tenders.
• Correct installation of the new schemes.
• Proper maintenance and periodic efficiency tests.
• New developments
• Liaison with contiguous authorities.

In cities and large towns the lighting arrangements are under the control of specialist lighting engineers. In the case of lesser communities, however, the lighting authority has been advised, either through the surveyor or directly by the local electrical of gas supply engineers who have employed lighting specialists on their staff. The recent advent of nationalisation in the Electricity Supply Industry and the impending repetition of this in the Gas Industry, should make no difference to this arrangement in principle.

With regard to the Area Electricity Boards, it is clear that they are prepared to continue the service. This arrangement has many benefits, not the least of which that it would help to bring fruitition, one recommendation of the Ministry of Transport, standard lighting on contiguous sections of roads by adjacent lighting authorities. Another relevant point is that much of the modern control of street lighting is an integral part of the electricity distribution system, and will become increasingly so in the future as large areas of street lighting are switched on and off en bloc by central control of one kind or another.

What of the future? The technique of street lighting will continue to advance from its present high standard in this country. The latest technique in fluorescent lamps to street lighting is bound to expand generally. Will this technique be superceded eventually by one in which the roads and pavemetns are lighting from strips and panels set in the facades of buildings.

The new British Electricity Authority and the Area Electricity Boards are fully alive to the importance of the sibject, and have not been slow to add a representative quota of delegates to this Conference.

There is no doubt as to the value of the APLE, particuarly as it provides the only common ground on which the problems can be discussed, the Association will march forward from strength to strength and will play an even greater part in the development of the lighting of our streets.

J. S. Smyth, B.Sc. (Eng.), A.M.I.E.E. Member of the Staff of the G.E.C. Research Laboratories
(Originally published as Communicaion no. 407)

Keywords: Lighting: Distribution, Lighting: Energy, Lighting: Installations, Lighting: Levels, Lighting: Luminaires, Lighting: Specifications, Lighting: Theory

Tuesday, September 14th, 1948

A reproduction of the paper was published in: Public Lighting, Vol. 13, No. 51. July-September 1948. This includes the discussion.

Abstract: History, description and summary of the unidirectional lighting system.

"Unidirectional lighting, being a new approach to the lighting of double carriageway roads, should be judged on its own merits and not only in the light of previous practice. The light output per 100' of road is only some 2000 lumens with 125 watt H.P.M.V. lamps spaced 150' apart: this, of course, is less than the recommended minimum of 3000 lumens, suggested in the Departmental Report of the M.O.T., yet the road brightness can be as high as that normally obtained with an output of 8,000 lumens, while revealing power is enhanced by a reduction in the brightness of light coloured objects. It seems clear, therefore, that while more experience is required before a final assessment can be made, it would be wrong to doubt the efficacy of the system merely because the power consumption is low."

PRINCIPLES
In the MOT Report, it was tentatively recommended that each track of a double carriageway road should be lighted independently. The Report pointed out that tehre was a need for considerable investigation "by appropriate modification of the distribution in the two directions along the axis of the road." The unidirectional system is an attempt to improve the lighting by such a modification; and the incidential reduction in the power required for a given standard of revealing power is of special interest at a time when restrictions are hampering the Public Lighting Engineer.

The system was mentioned at the 1937 Conference and in the years before the war a considerable amount of experimental work was done.

Experiments have shown that normal road surfaces reflect the light from a street lighting in rather unexpected and preferential ways. The smoothing action of traffic makes the surface behave very differently from a matt surface at the angles of reflection and view which are most important to the road user. As a consequence of this the bright area formed by a lantern upon the road surface does not extend beyond the lantern to the side away from the observer. Thus the light emitted in directions away from the observer is practically useless. It may contribute to a small extent in making the footpaths bright but even these surfaces are sufficiently far from matt for the contribution to be small.

In a two-way road, this "wasted" light emitted away from the observer is directed towards an observer facing in the opposite direction, and to him it is useful. Therefore if a conventional system is used for a one-way road, clearly half the light from the lanterns is wasted.

In a unidirectional system the first, and most obvious consequence of this restriction of light, is a saving in electricity consumption. For equal revealing power, the wattage in a unidirectional system may be reduced to about one-third of that in a conventional layout, partly because light is emitted in one direction only, and partly because closer optical control of the lamp is possible. In addition, it is legitimate to provide a beam somewhat narrower in azimuthal spread than normally required since on bends the lantern may be rotated to give the best results. (With two-way optical systems turning the lantern will throw one beam off the road if the other is aimed in the most useful direction and it is thus necessary to have a beam width sufficient to cover bends, though on straight roads such width may not be needed.) The reduction in power thus made possible may be of great importance in the lighting of double-carriage-way roads in outlying districts where power and cabling costs are high, and when fuel saving is essential.

Other advantages include: (1) The contrast between objects on the road and the road surface is enhanced. In a normal two-way road it is impossible to achieve this completely, since the light which makes the background bright for one direction makes the objects bright in the other direction. In a unidirectional system this difficulty does not exist. (2) In a double carriageway road the second carriageway appears to be unlighted and the driver is not distracted by glare and distraction due to the lamps on the other carriageway; at the beginning of double carriageway roads he is led naturally on to the proper track. (3) The clearness with which road junctions are seen. In a normal installation these revealing faces are illuminated to some extent by light emitted in the direction of traffic.

These advantages primarily benefit the motorist. Unidirectional lighting is not really suitable for built-up or shopping areas, where high illuminations are required on vertical surfaces, irrespective of their orientation. Although the road surface itself does not appear to be well lighted when looking towards the traffic, enough light is thrown across from the other carriageway to prevent any sensation of real darkness.

The glare from the lanterns is similar to that of a good non-cut-off installation if 150 ft. staggered spacing is used. It is possible to compromise between glare and road brightness uniformity by tilting the lantenr to suit specific conditions. Such a compromise is impossible with a two-way lantern of the non-focussing type, since depressing one beam will raise the other.

There's no reason why the unidirectional principle should not be applied to "cut-off" installations; the lanterns would hae a cut-off at about 75° on the side facing traffic with complete cut-off on the other side. Such an installation would combine the advantages of freedom from glare with high revealing power and low power consumption.

THE DESIGN OF SUITABLE LANTERNS
There is only one unidirectional lantern in production. The main beam is provided by a paraboloidal reflector below and behind the lamp, the distribution in azimuth being controlled by a fluted glass closing the mouth of the lantern. This glass may be changed according to the lamp in use: a clear or light diffusing glass is the most effective for an 80W fluorescent H.P.M.V. lamp or 45W sodium lamp (burning horizontally); but a fluted glass is used with 80-125W H.P.M.V. and 300W GLS lamp. The hemisphere above the lamp is occupied by a reflector which directs light into regions below the main beam, the sideways spread increasing as the direction approaches the vertical.

The body of the lantern is a large aluminum casting attached to the bracket arm by a universal coupling which permits adjustment both in elevation and azimuth. The lantern may thus be orientated to suit the spacing and to give the best performance on bends in any particular installation. However, on most occasions, a setting with the maximum intensity at 80° to the vertical to 8° from the street axis is satisfactory, so a sighting device has been designed to simplify erection with this standard setting.

PHOTOMETRIC PERFORMANCE OF UNIDIRECTIONAL LANTERNS
The candlepower distribution on the road and pavemetns from a unidirectional lantern should be similar to that from one side of any good lantern of normal design: light which would normally fall on houses may be reduced since the system is designed for open roads, and would not be recommended in built-up shopping areas.

A study of the isocandle diagrams shows there's little to chose between a normal and unidirectional lantern in the most important regions - the heads and tails on straight roads and on bends - which produce the bright cariiageway and illuminate the kerb lines and footpaths. On bends the unidirectional lantern scores if it is re-oriented to suit the conditions. The buildings are considerably better lighted by the 400 watt lantern, the more so as at mid-span two normal lanterns will contribute against only one unidirectional lantern - but as the unidirectional system is designed for open roads this is of little importance. Around the vertical ("cheerful appearance"), the unidirectional lantern gies a lower intensity in directions off the road, but the general illumination of the pavements is satisfactory. The glare intensities are much the same. The general conclusio nto be drawn is that the distribution and amount of light actually falling on the road from the unidirectional lantern is little different from that with conventional designs.

RECENT INSTALLATIONS OF UNIDIRECTIONAL LIGHTING
Before the war, the only installation was an experimental one on the Great Chertsey Road; however the excessive spacing of 180 ft. did not show the system at its best. The longest new installation is in Huddersfield whilst a Portsmouth installation has allowed further experimentation with 45W S.O. lamps.

References:
[1] Christopher, J. G., Smyth, J. B. and Waldram, J., M., GEC Journal X, No. 3, p205, August 1939.
[2] Some Further Experiments in Street Lighting, English, S., A.P.L.E. Conference 1937, Paper No. 3, p 16.
[3] Waldram, J., M., Illumin. Eng. XXVII, p. 305, October 1934.
[4] Waldram, J., M., Trans. I.E.S. (Lond.) III, No. 12, p. 173, 1938.
[5] British Patent No. 485801.
[6] Waldram, J., M., Trans. I.E.S. (Lond.) XII, No 8, p. 167, 1947.

S. English, D.Sc., M.I.E.E., F.Inst.P. Technical Director Holophane Ltd.
J. G. Holmes, B.Sc., A.R.C.S., F.Inst.P., F.I.E.S.

Keywords: Lighting: Colour, Lighting: Distribution, Lighting: Installations, Lighting: Luminaires

Tuesday, September 14th, 1948

A reproduction of the paper was published in: Public Lighting, Vol. 13, No. 51. July-September 1948. This includes the discussion.

Abstract: Examines the lighting of airfields and how street lighting could be misinterpreted as part of the airfield lighting. Explains the various Ministries lighting restrictions around airfields and how cut-off lighting may be used to mitigate. Various cut-off fixtures are then illustrated and compared. Suggests that controlled cut-off luminaires may be acceptable and some relaxation may be permissible in the future.

In misty conditions it is difficult to recognise the lights which mark out the landing strip. It is essential he should be given unmistakable assistance, both in the form of proper signal lights from the aerodrome and by way of eliminating any lights which might confuse him. An aerodrome runway is usally marked by two lines of contact lights between which the pilot makes his landing, and a straight road lit from both sides may show just the same appearance to the pilot.

This paper describes the series of airfield lights which may be seen by a pilot during his approach and landing, and indicates the lines on which the Ministry of Civil Aviation exercise control of street lights in the vicinity of the airfield. In most cases, a complete cut-off is required and representative street lighting lanterns are described. In some cases, a suitably controlled cut-off may be acceptable and data for several lanerns are given briefly.

THE LIGHTING OF AN AIRFIELD
Under normal conditions, the pilot is brought in by radio control until he can see the aerodrome beacon, which is generally a red or green light at several miles from the aerodrome, at which he should be able to make his final approach. RAF and civil aerodromes use different systems of guiding lights, largely due to the different conditions of operation. RAF aerodromes are encircled by a ring of white lights of about 100 candle power at four miles diameter, from which a line of sodium lights of 1000 to 2000 candle power, similar to inverted street lighting lanterns, branches off and leads to a tapering funnel, also of sodium lights, which in turn joins up with two lines of white lights, known as contact lights and giving 100 to 150 candle power, set in the runway itself. Civil aerodromes have a system of white and yellow approach lights which extend the runway by about ¼ mile. These approach lights may be a single line of yellow lights of low intensity, about 100 candle power, spaced every 300 ft., for use in clear weather, or may be a line of high intensity white lights, of several thousand candle power, with cross-bars of sodium lights to tell the pilot his position along the approach line in thick weather. Alternatively, some civil aerodromes have a narrowly tapering funnel consisting of two lines of sodium lights of 1000 to 2000 candle power also similar to inverted street lighting fittings. The system of approach lights is in line with the runway, at the beginning of which there may be a line of green threshold lights and a pair of angle-of-glide indicators which show yellow if the aircraft is too high, green if correct, and red if the aircraft is dangerously low.

The lights used in the runway are normally in two lines 150 ft. apart and the lights are spaced at 80 to 100 ft. intervals. The intensity of each light is relatively low, an average figure for the intensity being 100 to 150 candle power, although new contact lights are now available giving several thousand candles of a narrow angle so as to give greater assistance to a pilot under foggy conditions. If the pilot is slightly off course, these high intensity contact lights are of less advnatage, and the pilot has to do the best he can with the lights of only 100 candle power. Towards the end of the runway, the contact lights may be yellow and there may be a bar of green lights across the extreme end.

It is immediately obvious that sodium street lights may cause confusion with the approach lights and that the sequence of colours is very similar to many street lighting installations. But apart from the colour, the pattern of the street lights may be similar to that of an approach system or a line of contact lights. If the street lights are of high intensityu in upward directions, the risk of confusion will be greater.

Confusion was through very likely to arise between the lights of London Airport at Heath Row and the lights of the Bath Road. The Bath Road lighting consisted of vertical-burning(?) mercury discharge lamps in lanterns of orthodox design, giving 4000 to 5000 candle power at 10° below the horizontal and 1500 to 2000 candle power at 5° above the horizontal. The effect was so bad that these lights had to be reduced very greatly, and on the basis that it was impossible to say how little might be too much, the Ministry of Civil Aviation condemned the use of any lantern which gave any light above the horizontal for a distance of two miles along Bath Road.

THE ADMINISTRATIVE SCHEMES OF CONTROL
The Air Navigation Act, 1920, and the Air Navigation Order, 1923, include provisions that: (a) any light exhibited in the vicinity of an aerodrome, which by reason of glare is likely to endanger aircraft arriving at or departing from the aerodrome and (b) any light which is liable to be mistaken by the crew of an aircraft for an aerial light house, or for a light or part of a system of lights used for air navigation shall be extinguished or effectively screened on the direction of the Secretary of State or the Minister of Civil Aviation.

A memorandum on these provisions was circulated by the Ministry of Civil Aviation and the Air Ministry in 1945 dealt with street lighting, traffic signals and advertisements.

The present scheme of administration is that the Ministry of Transport sees all proposed street lighting schemes, and before giving approval, the schemes are passed to the Ministry of Civil Aviation, which passes them to the Airt Ministry of Admiralty. Lighting within half a mile from the runway in any direction and within two miles from the end of the runway comes within the scope of the powers granted to the Ministry of Civil Aviation and they may require dangerous lights to be extinguished; they are satisfied if the screening is efficient and the present standard requires that no light should be emitted above the horizontal.

Investigations are being made as to how much can safely be permiied above the horizontal and consideration has been given to factors of 2% of the total light output or 5% of the maximum beam intensity. The question of the additional cost of screening is still under discussion between the several authorities involved. This is a major matter as screened lights have to be mounted at a closer spacing than unscreened lights.

MODIFICATION OF EXISTING LANTERNS
Many street lighting lanterns give their main beams at about 78° from the downward vertical which is a gradient of 1 in 5 and therefore a screen should project from the lantern a distance of at least five times the vertical depth of the optical system. For Bath Road near Heath Row, Holophane Dilux lanterns with a prismatic glass bowl some 4½ inches deep were screened by two hoods each projecting 14 inches from the lantern and giving an overall width of 3 feet. By using such large screens, the distribution of intensity in the main beam was not seriously affected. The modified lanterns were mounted on the same posts as the original lanterns at 120 feet spacing in a staggered arrangement. There was a degree of patchiness to be expected and it would've been desirable to employ opposite arrangement in order to obtain a really good brightness distribution from the road.

For vertical-burning mercury lamps it would be necessary to have screens many feet long and also many feet wide to provide a cut-off without seriously impairing the illumination of the road. It is impracticable to provide cut-off screens on lanterns with vertical-burning mercury lamps, and that with other lanterns, the screens much be deep enough to reach down to the level of the bottom of the lamp or the refractor, and at the same time, large enough to avoid interference with the main beam; this involves an overall width of about 9 inches for every inch projection of the lamp bulb or refractor glass in the original lantern. With some sodium lanterns in whcih the glass panel is on 3 inches or 4 inches wide this can be done with fairly small screens but the lighting effect is, in general, inferior to that given by lanterns with larger glass panels. With filament lamps and glass refractors, the screens should conform to the same rules, and where the light is required in more than two directions the screen may have to be circular, the overall diameter being about 9 inches for every inch height from the top to the bottom of the optical system.

THE DESIGN AND CONSTRUCTION OF CUT-OFF LANTERNS
Cut-off lanterns are available for filament lamps, horizontal mercury discharge lamps, horizontal sodium discharge lamps, and and experimental design has been prepared for fluorescent lamps. Central suspension gives a very marked improvement over side mounting. For very wide roads, opposite location may be best, but staggered location is rarely satisfactory, because the cut-off can only be obtained by reducing the angular spread of the beam, and the size of the bright patch produced by each lantern is accordingly reduced. This leads to the need for closer spacing. The road surface brightness will be lower and less uniform than could be given by a controlled cut-off distribution for the same spacing. On the other hand, the cut-off lantern gives much less glare, and so the motorist has some compensation for the reduced illumination.

Experimental fluorescent cut-off lanterns have been produced i.e. a two 5-ft. fluorescent lantern with cut-off at 80° and the beam intensities are lower than normally obtained from street lanterns with fluorescent lamps. A satisfactory fluorescent installation usually requires a considerable number of lamps, and close spacing of these two-lamp fittings would be necessary in order to produce a road surface brightness comparable with that given by 5-lamp or 7-lamp lanterns.

CONTROLLED CUT-OFF LANTERNS
The present interpretation of "cut-off" by the Air Ministry means "no light at the horizontal or above" but there are controlled cut-off lanterns which give quite promising results and hopefully a more informed ruling will be made in the future. Many of these lanterns give a good distribution of light, although there's a small proportion of light which leaves the lantern in directions above the horizontal.

There are controlled cut-off lanterns for filament lamps, for horizontal-burning mercury lamps and also for sodium lamps (although the last named are extremely unlikely to receive approval in view of the risk of confusion with the yellow approach lights).

Typical controlled cut-off sodium lanterns give 10-15% of the total flux above the horizontal and 20-40% of the peak intensity in the horizontal direction.

Vertical-burning mercury lamps do not give a controlled cut-off in the usual sense of the term, but most of the lanterns employing horizontal burning lamps have the required property.

CONCLUSION
The requirements from the Ministries are reasonable but it introduces complications in street lighting which provide difficulties which are not insurmountable. The principle problem is that of additional cost as the lanterns may be more expensive and it's necessary to reduce the spacing to 100-ft. or less. The lanterns should be as high as possible and none should be mounted less than 25-ft. Excellent lighting can be obtained if the lanterns are spaced close enough and narrow roads should be lit by centre suspension; if the carriageway is too wide for centre suspension to be adequate, the lanterns should be arranged in opposite formation rather than in staggered formation.

Luminaires: Holophane Merrion Road Lantern, BLEECO P. J. Multilite, GEC Z 9443, REVO C 10644, Wardle Liverpool, Holophane Single-Piece Refractor Lantern, Holophane Dilux and GEC Z 8433 Blown Glass Cut-Off Lantern.

David M. Thompson, A.M.Inst.Gas.E., F.I.E.S. Distribution Superintendent, Gas Department, Wigan

Keywords: Lighting: Distribution, Lighting: Specifications and Lighting: Theory

Wednesday, September 15th, 1948

A reproduction of the paper was published in: Public Lighting, Vol. 13, No. 52. Special Conference Issue 1948. This includes the discussion.

Abstract: A resume of good practice in the design of a street lighting installation. Discusses Road Surface Brightness, Silhouette Vision and the ways different light distributions (non-cut-off, semi-cut-off and cut-off) affects this. Different road environments and characteristics are examined and proposals for different types of Group A lighting are discussed.

Many authorities, large and small, are responsible for street lighting. The majority cannot command the services of a public lighting engineer (due to their size) and therefore street lighting must be controlled by an official who has many other duties to perform and who cannot be expected to be a specialist. This paper is to help those officials.

First we should consider the methods by which good visiblity is attained. There would be no great difficulty in lighting streets or roads if it were not for the matter of cost. If we could use sufficient light source of ample power then the proble would be relatively simple - but the cost would be exorbitant.

ROAD SURFACE BRIGHTNESS AND SILHOUETTE VISION
Good visibility can be obtained at reasonable cost by means of road surface brightness and silhouette vision. Surface brightness is caused by the reflection of light from the road surface and light rays striking the road at a glancing incidence. Areas of brightness are produced on the road and they commence in front of the lamp position and extend towards the observer. By correct position of the lanterns, practically the whole of the road surface can be covered by bright areas, and objects on the road are seen as a dark silhouette against a light background.

TYPES OF LIGHT DISTRIBUTION
Methods of street lighting can be divided into three main groups:

• Type 1: Non-cut-off Lighting ("High Brightness"): Aim to make the greatest possible use of surface brightness. Maximum candle power occurs between 75° and 85° from the vertical and the candle power is well maintained up to the horizontal. It is usual for quite a large proportion of the light to be emitted above the horizontal.
• Type 2: Semi-cut-off Lighting: The maximum candle power is at about 75° and at 85° the candle power has fallen considerably below the maximum, but there is not a complete cut-off below the horizontal.
• Type 3: Cut-off Lighting: The light source is hidden when viewed from a distance. The maximum candle power is at about 70° and there is a fairly sharp complete cut-off below the horizontal.

The length of the bright area produced on the road surface is controlled by the distribution of the light from the lantern, particularly by the light emitted at angles near the horizontal. If the candle power emitted just below the horizontal is reduced, then the bright area will be shorter, and therefore the lanterns must be fixed closer together in order to ensure there are no dark patches between the bright areas produced by consecutive lanterns.

Similarly the width and shape of the areas of brightness are also affected by the type of light distribution. Type 1 distribution produces the narrowest bright area and is roughly T-shaped. Type 3 produces a wider area of brightness which is roughly egg-shaped. For Type 2, the width and shape are intermediate between the two.

A further difference is the amoutn of glare. For Type 1 glare will be at a maximum because a high candle power is emitted at angles near the horizontal and thus will be directed into the eyes of an observer. Such an installation can, however, be economical by reason of the longer spacing which is permissible. In the case of Type 3, glare is reduced to a minimum, but because of the short lenght of the bright area, the spacing must be closer and consquently more light sources are required. Type 2 is intermediate between the other two types, the amount of glare is moderate and spacing rather shorter than the maximum permitted is advisable. It thus provides a useful compromise.

It is seldom possible to adopt an average spacing equal to the maximum permitted owing to the necessity to allow for intersections, bends, etc., and for this reason it will be found that the spacing for Non-cut-off and semi-cut-off differs very little in an actual installation.

AREAS OF BRIGHTNESS
They are moving reflections which depend on the relative positions of the observer and the lantern, and on the nature of the road surface. On a matt road the bright areas are comparatively wide but on a road with a shiny surface they become narrower and brighter. When the road is wet, the bright areas become narrower and brighter, so causing stronger constrasts and this is hte reason why street lighting is not as good on a wet night.

The long portions of the bright areas always strethc towards the observer wherever he may be. Thus it is necessary, to create good visibility, that there should always be a lantern ahead of the observer, of the opposite side of the portion of road which it is desired to reveal. This is particularly important in the case of the diver of a vehicle as the driver travels forward, particularly round a bend, another lantern should come into view ahead of him as soon as the previous one moves out of his line of vision. The aim should be to provide a continuous line of brightness so that all the features of the road unfold before the driver.

Types of Street Lighting Installations
The various factors which make up a street lighting installation are:

• Type of light distribution from the lantern
• Mounting height
• Spacing
• Arrangement of lanterns
• Overhang
• Siting of lanterns
• Light output
• Type of road

THE APPLICATION OF GROUP "A" LIGHTING
The MOT REport purposely leaves the definition of traffic route ratehr vague, since the question must be largely decided by local conditions. The following criteria should be applied:
(1) Purely traffic routes in the outskirts of town where there is little pedestrian traffic and few intersections. In these cases, the most economical installation can be adopted with spacing at or near the maximum. Any three types of light distribution are suitable.
(2) Traffic routes in a built-up area where there are more side roads but the development is mainly residential or industrial. All three types of lightg distribution are suitable.
(3) Shopping streets, town centres and roads in or near the centre of a town. In these cases Type 2 distribution is most suitable although Type 1 can be used. Type 3 will cause a "tunnel effet" if used among buildings which are higher than the light source. Moreover, in a town centre or shopping centre, the buildings should be reasonably illuminated. The spacing should not be more than 120 feet and can be less. Staggered arrangement is suitable, but in the more imporntant of such streets consideration shuld be given to the adoption of opposite arrangement. Where vehicular and pedestrian traffic is particularly dense, too much reliance should not be placed on road surface brightness and more light should be provided, preferably by providing more lanterns at closer spacing. On roads of this character, monochormatic lighting is wholly inappropriate and light of a more natural character should be adopted (gas, GLS or tubular fluorescent).

SELECTION OF INSTALLATION TO SUIT THE ROAD
The Public Lighting Engineer should visit and the xeamine the roads which it is proposed to light and then decide which types of installations will be most appropiate in each case. The installation should then be designed in accordance with the Specification or Code of Practice.

GROUP B. THE LIGHTING OF ROADS OTHER THAN TRAFFIC ROUTES
As important and requires equal care to obtain a good installation. Fundamentals essentially the same. There has been no Draft Specification for Group B so must go back to the MOT Final Report. By reason of the comparatively low mounting height, the only suitable type fo light distribution for Group B is Type 1. (Type 3 is quite unsuitable at 15 feet mounting height and even Type 2 would give a very uneven appearance to the road.

THE APPLICATION OF GROUP B LIGHTING
The lower figure of lumen output should only be used for purely residential roads and higher lumen outputs and closer spacing should be adopted on the important roads having a greater volume of pedestrian and vehicular traffic.

The minimum standard of Group A lighting is designed to obviate the use of headlights but they may be necessary in Group B lighting. Many very small local authorities an only afford to use Group B lighting even on a traffic route, and in such cases quite satisfactory results can be obtained if the installation is properly and generously designed.

See Side Street Lighting presented to Conference last year.

SHOULD THERE BE A THIRD GROUP?
A third group would be helpful with a mounting height of 20 feet. This would meet the requirements of many roads where the expense of Group A lighting is not justified, but require better lighting than Group B, especially as regards mounting height. (There are cases of wide Group B roads where lanterns at 15 feet mounting height slightly behind the kerbline leave a dark lane in the centre of road. And there's the case of the more important Group b road which is tree-lined and where the lanterns tend to be obscured by the trees.) In both cases a mounting height of 20 feet would permit of some overhang with consequent improvement of the lighting. The suggested mounting height should also make it possible to use lanterns with semi-cut-off distribution and consequent reduction in glare.

J. N. Aldington, B.Sc., Ph.D., F.R.I.C., F.Inst.P., F.I.E.S. Assistant Works Manager, Siemens Electric Lamps and Supplies, Ltd.

Keywords: Lighting: Lamps

Thursday, September 16th, 1948

Abstract: The history of artifical lighting goes back for thousands of years, but the electric lamp is a product of only about the century of effort. That the last two decades have seen the most rapid advances yet made is no doubt due very largely to the growth of lamp research organisations devoting their efforts to pure and applied lamp and lighting developments. We are living in an age which, more than any other, demands the maximum co-operation of the lamp research engineer, the lighting engineer and the public authorities responsible for lighting installations so that the advances of the years can be harnessed to the benefit of mankind.

INTRODUCTION
1. The desire to produce more effective conversion of electrical energy into light had led to the investigation of not only new methods but also of new materials and new techniques.
2. We can observe the influence of lighting requirements on lamp design.

HISTORICAL DEVELOPMENTS
In the past, man discovered that heat and light were probably different manifestations of one common form of energy change. Gradually the fact emerged that the hotter a substance was made the brighter it became, and that simultaneously the colour of the light more nearly approached the colour of daylight.

It was natural that the first serious attempt to produce the electric lamp should be direted towards making use of the heating effects of an electric current, both by producing sparks in air and by heating to incandescence a wire through which the current passed. However it was not until a steady source of electric power became available that the real possibility of the electric lamp dimly emerged.

Soon after Volta announced his electric pile in 1799, a number of workers concluded that the source of electricity was chemical action. This led to the production of a number of distinct types of so-called primary cells in which dissimilar metals were immersed in an electrolyte. In 1808, Davy demonstated the electric arc. De La Rue in 1820 designed a lamp in which a platinum wire was mounted in a glass tube closed with brass camps. Grove developed a powerful nitric acid battery in 1839 and he experimented with a spiral of platinum wire operating in a glass tumbler inverted over water. M. J. Roberts in 1842 described the results of glowing a graphite rod in vacuo - a forerunner of the carbon filament lamp. Starr demonstated a platinum filament lamp in 1845 - he investigated quantitatively the effect of different filament lengths by using strips of platinum foil and produced a successful vacuum lamp. The chemist Liebig published in his Letters on Chemistry in 1851 that it would be possible to have "whole cities lighted in the most brilliant manner by lamps without flame, without fire and to which air has no access." In 1859, Professor M. G. Farmer lit up his house with a number of electric lamps.

Swann and Edison succeeded in producing commercially carbon filament lamps in 1879. Improvements followed rapidly, and the first sealed-in lamps in which filaments of carbonised bamboo were mounted in exhuasted gass envelopes were rapidly replaced by squirted cellulose filaments prepared and carbonised in accordance with the Swan patents.

The carbon filament lamp enjoyed an undisputed field until about the year 1900 as the Nernst Lamp, first patentened in 1897, was produced commerically in Great Britain, German and America. The British Company soon abandoned their interests. (The Nerst Lamp had a negative resistance temperature coefficient and required a stabilising resistance - but the development of metal filament lamps showed more immediate promise so the Nerst Lamp fell into obsolescence.) In the history of electric lamp developments many interesting lines of research have been imperfectly investigated due to the introduciton of new lamps of considerably higher efficiency which on accoutn of their more immediate usefulness, rendered obsolete the earlier forms. Who can say that beuase of this effect the world has not lost man promising sources of artifical light?

In 1902, W. von Bolton produced tantalum in a pure form and was able to draw it into a wire and demonstrate its value for electric lamps. By 1910, manufacture of tantalum lamps had been established by Siemens Brothers in the UK. Metal failment lamps embody radical depatures in design from carbon filament lamps as a relatively long length of wire has to be accommodated requiring a number of filament supports giving rise to the so-called cage construction.

It had been appreciated that the higher the temperature at which the lamp filament could be operated the more efficeint would be the conersion of electrical energy into light. Interest in the metallurgy of the rarer metal of higher metlting and boiling points was therefore stimulated.

It was the development of osmium filaments which led to a similar method being used to create tungsten filaments. It was the development of methods for producing drawn tungsten wire which established the incandescnet lamp industry on a firm basis and opened up the way for the rapid expansion which followed.

In most types of tungsten filament lamp the tungsten wire is coiled into a compact helix which may itself be further compacted by being re-coiled or by being bent into a variety of forms according to the particular task which the finished lamp has to perform. The coiled formation serves a two-fold purpose. Firstly, it reduces the effective surface area from which energy is lost to the surrounding gas by conduction and convention and it produces a ligth source of a more concentrated form.

In the modern incandescent lamp, the tungsten filament is designed to oeprate in an atmosphere of inert gas contained in the glass bulb. Generally, the gas fillingconsists of argon, nitrogen, or a mixture of these gases, but krypton is used for the gas filling of a relatively small proportion for specail lamps used in portable lighting equipment in the coal mines.

Only gases of low thermal conductivity are suitable for filing electric lamp bulbs as the presence of the gas increases thermal losses from the filament. There is a marked decreased in the rate of evaporation of tungsten from teh filament due to the presence of the gas. It is now stanard practice to make all high voltage lamsp of 40W and upwards of the gasfilled type, while below 40W the gain due to gas filing is problematical, thus 15-25W GLS lamps have the filament operting in a vacuum.

An essential fature of a gasfilled lamp is the use of a coiled filament. The comparative shortness of the coil compared with the length of wire to produce it, not only reduces thermal losses, but also results in a compact design of filament which requires a minimum number of filament supports. The supports are generally made from molybdenum wire and a balance must be struck between the need for adequate strength and for reducing to a minimuim heat losses by conduction through the supports.

CHARACTERISTICS OF TUNGSTEN FILAMENT LAMPS
V = rated voltage.
V₁ = operating voltage.

Luminous flux = (V₁ / V)^3.6

Power consumed = (V₁ / V)^1.52

Luminous efficiency = (V₁ / V)^2.1

Lamp life = (V₁ / V)^-13.5

For the lamp life, a 5% increase in voltage will approximately halve the life of a tungsten filament lamp.

As occasion demands, lamp specifications are revised and so furnish an increasing account of progress in the field of tungsten filament electric lamps. The latest specification requirements are based on a statistical approach to the subject of lamp quality. Given a batch of 100 lamps, it is possible to predict with reasonable accuracy the average life and behaviour of the batch. No-one can accurately state what the performance of any given lamp will be. For this reason the British Standard Specification, for electric lamps give the average expected performance for given test quantities, and represent the best available data regarding the quality of modern tungsten filament lamps.

ELECTRIC DISCHARGE LAMPS
Davy's first arc lamps was the precursor of the modern high current density arc and the starting point for the sealed vapour and gas discharge lamp of the last twenty years.

Prior to 1930, apart from the carbon arc, the production of light by the electric discharge was confied to high wattage tubes of neon and Cooper Hewitt mercury vapour lamps. The Moore carbon dioxide tube was too large and too fragile for anything other than special purpose applications.

Development work on low-loss electrodes reached fruition in the late 1920s, so a range of mains voltage discharge lamps was rapidly developed and progress still continues. The electrodes of all discharge lamps are sealed into glass or quartz envelopes which may be of tubular or spherical form. The nature of the particular transparent material must be determined after considerations of such factors as the chemical and physical properties of the discharge, the temperature necessary to produce the requisite vapour pressure if the discharge lamp is of the metallic vapour type, and other considerations such as the relation of the expansion co-efficients of the glass to those of the most suitable metallic sealing medium.

Particularly in the case of the higher pressure mercury vapour lamps and the sodium lamp, the development of a suitable glass for the envelope has involved a great deal of investigational work as it was found that not only were special properties required of the material but its treatment during the fabrication of the lamp affected the performance. It was also necessary to develop methods for sealing hermetic conductors into these various glasses. For some glasses special composite wires of the copper sheathed nickel iron type are suitable while other glasses require molybdenum or tungsten wire specially prepared to enable a high tempeature hermetic seal to be produced.

It is necessary to arrange the dimensions of the glass or quartz envelope and its shape in relation to the discharge so that the corret discharge conditions are produced without overloading. The special borosilicate glass used in the street lighting type of mercury vapour lamp is suitable for operating at temperatures which will give a mercury vapour pressure of 0.5 to 1 atmosphere. If a lamp is designed for much above these temperatures then premature darkening of the glass may result.

SODIUM VAPOUR LAMPS
Little fundamental development has taken place in the last few years.

In the UK, manufacture is almost entirely limited to the parallel operation design of lamp for mains voltage operation. In this lamp, which is operated from a leakage reactance transformer, the light source consists of a discharge tube being bent into U form for compactness. It is mounted inside a Dewar flask type of outer jacket and the discharge tube proper is separate from the outer jacket and can be removed therefrom for replacement purposes.

Emits its dominant radiation from the sodium doublet at 5890-5896 AU. This radiation is the resonance radiation from the sodium atom and any increase in loading or temperature causes absorption of the reasonance radiation and a reduction in efficiency without change in colour.

The indications are that this type is near to the peak of its development although in the laboratory under very special conditions considerably higher efficiencies have been obtained. The laboratory conditions are unlikely, however, to be reporduced in commerical forms of lamp. Its main disadvantage being the relatively small total output as the largest lamp at present made is rated at 140 watts and the monochromatic nature of the radiation which limits the use of the lamp to such purposes as street lighting.

MERCURY LAMPS
Mercury lamps fall into five main classes:

• 1. Low Pressure Lamps.
• 2. Medium Pressure Lamps (MA)
• 3. High Pressure Lamps (MB)
• 4. High Brightness Air-Cooled Lamps (ME)
• 5. High Brightness Water-Cooled Lamps (MD)

FLUORESCENT LAMPS
The modern mains fluorescent lamp and its application was the subject of an admirable survey by Davis and Sinclair before this Association two years ago. Since then new sizes of lamp have been introduced, some of them suitable for series operation on mains voltage. Two of these are the 20W and 40W sizes which, although entirely different lamps, are of the same physical dimensions. The series operation of short lamps will make them attractive for certain street and outdoor lighting installations as will as for indoor lighting purposes.

MEDIUM PRESSURE LAMPS, TYPE MA
It has been the subject of continuous development. This development has in the main been directed towards improvements in the electrodes upon which the lumen maintenance largely depends. New methods of fabrication have also been evolved and new manufacturing techniques have been developed. The result of all this work has been a continuous improvement in the lamp characteristics.

The Dual type lamp (MAT) continues to be very important. An automatically operated bi-metal switch shorts out a portion of the filament when the lamp has reached the fully run up condition. At no stage therefore in the run up cycle of the lamp is the filament overloaded and when the arc tube voltage has reached its normal full operating value the operation of the automatic swtich brights back the filament to its designed brightness.

The MA/F lamp is a mercury cadmium zinc lamp mounted within a specially shaped outer bulb which is coated internally with orange fluorescing powder. The powder serves to increase the red component in the emitted light, and improves to some extent the colour rendering effects.

The MA/H lamp operates at a slightly lower pressure than the normal lamp. It can be operated horizontally or in any position without the use of an arc centring device. This facility is obtained at the expense in a slight sacrifice in efficiency.

If it is desired to operate the MA/V lamp horizontally, a lamp fitting must be provided with a magnetic arc centring device. The magnetic field so produced counteracts the upward movement of the arc, which results from convection currents. The use of the magnetic centering device not only prevents overhating of the inner tube but allows the arc to develop its full efficiency.

HIGH PRESSURE MERCURY LAMPS, TYPE MB
Arc is contained within a quartz tube and at present only 80W and 125W ratings are available for general lighting purposes. When it was found desirable to introduce medium pressure mercury vapour lamps in wattages less than 250W, there was a serious falling off in efficiency with lamps in which the mercury vapour pressure was limited by the characteristics of the borosilicate glass tube. An increase in the voltage gradient in the arc brought about by increasing the mercury vapour pressure was found to give an increase in efficiency. The necessary operating conditions to take advantage of this effect could not be obtained with a glass envelope and it was necessary to develop means for using quartz bulbs.

The quartz tube required the development of hermetic molybdenum seals through quartz. It is only required to carry a few amperes. In practice, tubular quartz high pressure mercury vapour lamps, type MB, have efficiencies of the order of 40 L/W at 125W, while the 80W lamp has a somewhat lower initial efficiency. Experimentl MB lamps loaded to 250W can be made with initial efficiencies of the order of 50 L/W, while a lamp designed for 500W has an efficiency of some 55 L/W. These are for lamps made by laboratory techniques which are not very suitable at the moment for mass production.

The MB lamps of 80 and 125 watt rating are available not only in normal pearl finished outer bulb but also in tubular form with a specially stabilised arc. Colour modified tyeps are also made where the outer bulb is thinly coated with powders fluorescing in the orange and blue regions. The so-called black glass lamps also employ MB type quartz inner tubes, the outer bulb made from a glass whose effective transmission lies between 3000-4000A - they provide a powerful source of near ultra-violet radiation.

HIGH BRIGHTNESS LAMPS, TYPE ME
Air-cooled. Low voltage, high current. Only to be used in special luminaires. Colour modified versions may be used for technicolour film studios.

Not used for street lighting.

HIGH BRIGHTNESS WATER COOLED LAMPS, TYPE MD
Water-cooled. 500W and 1000W sizes standardised during the early years of the war.

Not used for street lighting.

GAS DISCHARGE LAMPS
This type of electric discharge lamp in which a high current density discharge takes place in a comparatively high pressure of inert gas has been the subject of considerable research and development. Gradually learning how to harness the electric discharge from gases which appeared unlikely sources of efficienctly produced visible light.

Argon will emit white light. Krypton is even better. And xenon filled lamps have already been made with efficiencies of the order of 50 L/W.

These gases are used in flash discharge tubes.

Not (currently) used for street lighting.

THE GAS ARC
New range of lamps announced in 1947. A high current, low voltage arc takes place in argon, krypton or xenon which produce efficiences of 15 L/W to 40 L/W according to the particular gases employed and the loading. The energy distribution in the spectrum of this lamp closely approaches that of sunlight. Applications include photographic and film studio lighting, general floodlighting and large area illumination where daylight quality is a necessary feature.

References:
[1] The Development of the Electric Incandescent Lamp Bernard P. Dudding and Colin J. Smithells, Beama, October and December 1923
[2] The Evolution of the Electric Lamp J. N. Aldington, Endeavour, Vol 11 No. 6, April 1943
[3] Darkness into Daylight W. T. O'Dea, Ministry of Education, Science Museum, 1948
[4] Eelctric Lamps and Kindred Devices. Historical Introduction and Production of Tungsten Wire J. N. Aldington Siemens Engineering Bulletin, No. 232. May, 1947
[5] Bright Light Sources Part I J. N. Aldington Transactions of the Illuminating Engineering Society, Vol. X, No. 1, January 1945
[6] Bright Light Sources Part II J. N. Aldington Transactions of the Illuminating Engineering Society, Vol. XI, No. 2, February 1946
[7] The Application of Modern Flash Discharge Tubes C. R. Bicknell Transactions of the Illuminating Engineering Society, Vol. XIII, No. 1, 1948
[8] The Flash Tube and Its Applications J. N. Aldington and A. J. Meadowcroft The Institution of Electrical Engineers, December, 1947

Charles N. Melton Street Lighting Inspector, Dagenham.

Keywords: Lighting: Distribution, Lighting: Maintenance, Lighting: Safety, Lighting: Signs, Lighting: Specifications, Lighting: Theory

Friday, September 17th, 1948

Abstract: Investigation into the factors which promote safety in a lighting installation. These include the type of lighting distribution (silhouette or direct), glare and how it can be avoided, the lack of uniformity between installations, the safety of column materials, the problems of trees blocking illumination, sign and guard post lighting, pedestrian crossing lighting, and planning maintenance and cleaning.

INTRODUCTION
The war-time blackout was certainly no help to road safety. But even with the resumption of street lighting, of a restricted nature, the number of accidents occuring between dusk and dawn is still sufficiently formidable to warrant earnest attention.

A great contribution to road safety was made by the MOT Departmental Committee on Street Lighting. This has formed the basis for a good code of lighting practice, and the consequent Draft Specification for Street Lighting placed these recommendations in a more concrete form.

For effective application of the principles laid down in these publications, however, a certain amount of practical experience is of considerable value.

A GUIDE TO REQUIREMENTS
Safety on the roads is dependent chiefly on the ability of the road user to see clearly all objects, whether still or moving, in the path of travel, and what is more important, on the ability to see them in sufficient time to appreciate fully, all the conditions involved and decide on what action if any, is necessary.

For reasons of economy we are limited to the use of comparatively low values of illumination for lighting our roads and it has become generally accepted that the most effective method of utilising these low values is by means of careful control and projection of the light in order to exploit the reflective properties of the road surface and produce a high background brightness against which objects can be seen as silhouettes.

Silhouette vision can only be effective provided there be a sufficient length of roadway in the field of view in order to provide the necessary background against which objects of a height, say, three feet can be completely observed, and for conditions of complete safety this length will of necessity vary according to the speed of travel of the observer, taking into account such factors as braking distance and reaction time. Certain minimum values, according to speed, have been suggested in the past.

If the traffic density value exceeds a certain value, consideration should be given to the provision of a system more in the nature of direct lighting as vision under these circumstances will tend to be dependend on adequate light on the vertical surfaces of objects rather than on the horizontal surface of the roadway. This would mean an entire reversal of the principle of silhouette vision, as equipment would be necessary for the projection of light in the same direction as the flow of traffic instead of against it, particularly in the case of very congested areas. In many built-up areas, traffic conditions will vary considerably according to the time of day, so that silhouette vision may be adequate for the major part of the night, but direct vision may be called for over a comparatively short period. A traffic census for any area would give a good guide to the actual safety reqirements, and whether the conditions just referred to do apply, in which case the provision of a special supplementary lighting scheme, possibly in the form of additional lanterns for use over a short period, would be worthy of consideration.

Local traffic will be familar with a variety of routes in the area, in addition to main traffic routes, but these may be listed as Group B roads, and will have an intensity of illumination considerably lower than the traffic routes. During the winter months, when the lighting is in use at a early time in the evening, these alternative routes may tend to be avoided owing to the greater attraction of the higher intensities of the main routes. Some special consideration should be given to routes of this nature, with an intensity of lighting higher than Group B, but less than Group A. In this way it might be possible to produce safer travelling conditions in the main routes by a reduction of the traffic density. Full co-operation with the Police Department, with a view to obtaining particulars of all accidents which occur during darkness, will give a guide as to where special considerations are necessary, in the event such accidents being attributed to inadequate lighting.

GLARE
The application of silhouette vision brings in a feature which may be a source of considerable danger, namely disability glare. This forms one of the chief causes of the reduction of visbility in a lighting installation. This glare is referred to as "veiling brightness" and important factors in its calculation are the angle between the line of sight and a line drawn from the eye to the light source and the candlepower intensity directed towards the eye. The ideal is a complete absence of glare, but economic considerations limit the methods by which this may be obtained. Some degree of glare is almost certain to be present in a lighting installation.

The adoption of high-mounted lighting units is of great benefit, but we are limited by economic considerations and difficulties in maintenance, so it would appear the greater improvements are likely to occur by modification of the existing types of lantern with a view to reducing the intrinsic brightness of the light source and increasing the flashed area of the lantenr. This is borne out by the very favourable comments made since the advent of experimental installations using tubular fluorescent lamps. The technical features of the fluorescent lamp appear to be ideally suited to assist in fighting the glare problem.

Vehicle headlights are a major problem but an adequate Group A installation will obviate the need for these. There is a point where traffic leaves the main road and passes into the side streets where the natural reaction to the lower brightness level will be to turn on the headlights with consequent discomfort and possible danger to traffic proceeding in the reverse direction. The obvious solution would be gradation of the lighting from the main road to side streets but this idea has since been rejected as it is considered that a greater degeree of safety is provided by the obvious difference in the two classes of lighting. Another solution is the application of polarised light to be used with headlights. The correct type of materials have not been available at reasonable cost although various grades of plastic polarisers have been developed in America but these need investigating.

LACK OF UNIFORMITY IN LIGHTING
This matter was discussed in 1946 and the solution appeared to be largely a matter of economics. It is sufficiently disconcerting and dangerous for traffic to have to pass through a variety of intensities of illumination and various colours of light source. But the greatest danger occurs where the built-up area ends and the open country begins, as this is too often the point where lighting entirely ceases, and the sudden transition from cparatively good light to complete darkness has frequently been the cause of accidents. Changes in the colour of lighting along a traffic route do not constitute as serious a menace but this feature would be better avoided and in the majority of cases would merely mean co-operation between the authorities involved. In certain cases, an unfortunate feature has been the trouble caused by a certain types of light source in connection with railway transport, where confliction with railway signals has compelled the adoption of a type of light source different in colour from that used in the main part of the installation, to avoid the excessive screening which would be required if the original lamps were retained. As the MOT is now the central authority for street lighting, it is hoped more attention will be given to authority.

THE USE OF SAFE EQUIPMENT
In particular, this includes the lamp columns. Quite recently British Standards Specifications have been published in connection with these, and it is rather surprising that cast-iron columns are still regarded as a likely type for modern usage. Lamp columns are frequently involved in minor accidents and the tendency of cast iron to fragmentation often leads to far-reaching effects which might be avoided by the use of steel or reinforced concrete.

AIDS AND HINDRANCES TO VISIBILITY
It is now generally recognised that the background forms a most important part of the field of view, and modern types of lanterns are designed to ensure its adequate lighting. It is only in the built-up areas where continuous backgrounds in the forms of buildings and walls, etc., are likely to be met with. The provision of a lighter background by the use of light coloured stone for new buildings or light paint in existing brickwork, etc., will prove a great aid to the improvement in visibility.

On straight sections, the presence of treets mounted in a continuous line along the edge of the footpath almost entirely prevents the footpath from being visible to the traffic, so that in perspective there is no effective background against which a pedestrian can be seen when stepping into the road. Trees should be placed at the rear of the footpath which would aid visibility and obviate the need for a centrally suspended system. Trees in the vicinity of lamps should be kept well trimmed at all times, in order to prevent obscuration and the formation of intermittent shadows on the road surface.

TRAFFIC LIGHTING
The MOT Report gives recommendations for standardising the various types of road traffic signs. Recommended values of brightness are given. The values of 15 to 20 eFC is considered to be sfe as it's not likely to cause troublesome glare or distraction in poorly lighted streets. This can only be true provided the brightness is evenly distributed over the whole surface of the sign.

These remarks also apply to illuminated guard posts which are used on island refuges. Tests show the diversity of brightness is not as great. However the diversity is greater than the recommended limit of 4 to 1. The MOT Report recommends an average brightness of 8 eFC. Certain parts of the guard post may be at dangerously high level of brightness, and this is intensified by the fact that the limited height of the post may cause the excessively bright parts to fall almost exactly in line with the eye of the driver. The particular danger in this case lies in the fact that these refuges are almost invariably associated with pedestrian crossings where visbility should be of the highest degree. A separate British Standard is required.

PEDESTRIAN CROSSINGS
It is proposed in the future to illuminate internally the orange beacon globes, principally for the benefit of the pedestrians, but with the suggestion that this feature will also be of some use to the road user.

It is not considered that special lighting is necessary as a good installation of street lightin will automatically ensure adequate visbility of persons using the crossing. What is really required is some incentive for pedestrians to actually make use of the crossing instead of stepping into the roadway at odd places along the route. It will be hoped that the illumination of the beacon globe will provide something of this nature.

MAINTENANCE
The importance of good maintenance cannot be over-emphasised, for by lack of attention to this, an otherwise good installation may be entirely ruined and rendered dangerous. Where conditions permit, the maintenace work should be carried out by a staff which is entirely confined to this class of work and not likely to be diverted to work in other departments.

There is the necessity for designing a system which is particularly suited to the district under consideration. The depreciation of the illumination due to the collection of dust and dirt, cannot be fully appreciated unless actual tests are taken under service conditions over a period of time. The results may indicate that certain areas, owing to their particular location, may require more frequent cleaning.

There must also be considered the lighting-up time table. There is a noticeable fall in daylight illumination soon after the sunset time is passed, but this fall does not continue at a constant rate, but at a steadily increasing rate. Consequently it is advisable for all forms of automatic control to be set to operate at times which are slightly ahead of those which are usually found in standard time tables. By this means a safeguard is provided against inadequate lighting during the short dangerous period of twilight.

References:
[1] Road Lighting and Traffic Density H. L. Juliusburger
[2] Discomfort Glare in Lighted Streets R. G. Hopkinson
[3] Lighting of Bends and Junctions F. F. Middleton
[4] A New Lighting-up Time Table G. H. Wilson
[5] Illumination Engineering Boast
[6] MOT Final Report on Street Lighting
[7] MOT Report on Traffic Signs