Annual Conference at Bournemouth
September 5th-8th, 1938

Abstract: Descriptions of lanterns and equipment displayed by Measurement Limited, Kurt Erlach Limited, The Electric Street Lighting Apparatus Co., Spun Concrete Ltd., W. Parkinson and Co., Radiovisor Parent Ltd., Engineering And Lighting Equipment Co., Ltd., The Horstmann Gear Co., Ltd., Holophane, Limited, Philips Lamps, Ltd., British Sangamo Co. Ltd., Simplex Electric Co. Ltd., Gowshall Limited, Automatic Telephone And Electric Company Limited, Keith Blackman Ltd., C. H. Kempton and Co., Ltd., Siemens Electric Lamps And Supplies Ltd., REVO Electric Co., Ltd., Walter Slingsby and Co., Ltd., Metropolitan Vickers Electrical Co., Ltd., The British Thomson-Houston Co. Ltd., The General Electric Co., Ltd, Venner Time Switches Ltd., William Sugg And Co., Ltd., British Foreign and Colonial Automatic Light Controlling Co. Ltd., Gas Meter Company Ltd., Foster And Pullen Ltd., Concrete Utilities Ltd., Stanton Ironworks Company Ltd., Bromford Tube Co., Ltd. and Stewarts And Lloyds, Ltd.

Adverts: Spun Concrete Ltd., British Electrical Development Association, W. T. Henley's Telegraph Works Co., Ltd., Measurement Limited, Kurt Erlach Limited, The Electric Street Lighting Apparatus Co., W. Parkinson and Co., Radiovisor Parent Ltd., Engineering And Lighting Equipment Co., Ltd., The Horstmann Gear Co., Ltd., Philips Lamps, Ltd., Holophane, Ltd., British Sangamo Co. Ltd., Metropolitan Pipe And Pole Company Ltd., The Brighton Lighting And Electrical Engineering Company, Ltd., Simplex Electric Co. Ltd., Gowshall Limited, Automatic Telephone And Electric Company Limited, Keith Blackman Ltd., C. H. Kempton and Co., Ltd., Siemens Electric Lamps And Supplies Ltd., REVO Electric Co., Ltd., Walter Slingsby and Co., Ltd., Falk, Stadelmann and Co. Ltd., Metropolitan Vickers Electrical Co., Ltd., The British Thomson-Houston Co. Ltd., Newport And South Wales Tube Company Limited, Automatic Light Controlling Co. Ltd., Venner Time Switches Ltd., William Sugg And Co., Ltd., Gas Meter Company Ltd., Foster And Pullen Ltd., The Horstmann Gear Co., Ltd., Concrete Utilities Ltd., Stanton Ironworks Company Ltd., Bromford Tube Co., Ltd., Stewarts And Lloyds, Ltd., Whelmer Gas Mantle Co., Amal, Ltd., British Commercial Gas Association, Edison Swan Electric Co. Ltd., Standard Telephones And Cables Ltd., Poles Ltd, County Of London Electric Supply Co. Ltd. and The General Electric Co., Ltd.

A paper was to be given by Monsieur Andre Janet, the Lighting Engineer of Paris, who was to give an account of public lighting in France. However, it never happened.

Various types of lamp standards were erected down Bradley Road and outside the Exhibition Hall.

Thirty two stands were erected inside the Exhibition Hall.

Mr. C. H Woodward, A.M.I.E.E.
Electrical and Public Lighting Engineer, Bournemouth

Keywords: APLE: Conference, Lighting: Education, Lighting: Floodlighting, Lighting: History and Lighting: Specifications.

Tuesday, September 6th, 1938

Summary published in: Public Lighting, Vol. 3, No. 11. September 1938

Abstract: A rambling paper with no discernable theme. Woodward talks about a number of different disconnected subjects including recent developments, the need for Public Lighing Engineers, and the recent history of street lighting in Bournemouth.

Progress in public lighting is being brought about mainly by the growth and speed of transport, together with the demand for greater personal safety. The Public Lighting Engineer is a product of recent years. However, there is prodigality of types and methods of lighting, some of which is ill-arranged and misdirected light and dim installations are a problem. It should be the aim of all authorities to produce a better balance of lighting.

There are two items available to local authorities to enable them to secure a better balance:

The Final Report of the Ministry Of Transport

The trained Public Lighting Engineer to advise and carry out the recommendations of this report.

"It is not many years ago when the lamplighter pushed a brass-bound glorified broom-handle, with a colza oil lamp at the top, up through a trap door in the street lantern to light the lamp. The "scheme of lighting" was just a lamp at the junction of roads and an additional lamp here and there, with large enscrolled, massive lamps supported by dolphins rampant for adding dignity to such places as market squares or town halls. This Victorian idea is passing."

Public lighting engineers are still rare, and many lighting engineers have additional responsibilities. More should be done to promote the lighting engineer in the local authority. The new Diploma (offered by the APLE) will supply sufficient training and it is hoped that larger towns (who can't afford dedicated public lighting engineers) will appreciate that undivided attention to this service will result in an all round improvement.

The competing systems of gas and electricity will ensure that growth and constant improvement is made.

Features of outstanding merit over the preceeding year are:

The culmination of the Association's efforts to assure the educational status of the Lighting Engineer.

The issue of the Final Report on Street Lighting by the Ministry Of Transport.

Lighting and Air Raid Precautions.

It is hoped that the concept of visibility will be standardised in the near future. "We face a new year in the hope that something will soon be available whereby the degree of visibility at any place can be referred to a set standard, and to measure the variation in visibility with changing conditions and surroundings such as the change in visibility which occurs with a change from wet to dry conditions or the substition of a rural background of trees and shrubs by the removal of advertisement hordings or the reverse effect by the erection of buildings."

It is also hoped that there should be greater uniformity in road surfaces (with respect to silhouette vision and the absorption factor of different repair patches).

A "Town's Amenities" should present a light picture after daylight passes. "Floodlighting" is not acceptable. A good solution can only be accomplished by co-operation between the architect, town planner and Lighting Engineer. A town should be "brightened" by chosing building materials with a view to producing lighter backgrounds, the provision of light backgrounds at crossings and junctions, the provision of light surfaced pavements bounded with a well-defined kerbline, and that the surface of the road should be kept in a uniform condition of "brightness characteristic."

When the Association Of Public Lighting Engineers visited Bournemouth in 1929, the "brightness" and the "illumination" caused the town to take stock, and it became conscious of the fact that things could be improved. This resulted in the improvements in the town.

Mr. J. F. Colquhoun

Keywords: Lighting: Specifications

Tuesday, September 6th, 1938

Summary and discussion published in: Public Lighting, Vol. 3, No. 11. September 1938

Abstract: Summary of the contents of the Final Report. Colquhoun notes some of the criticism and questions about the Report, and deals with some of them, leaving others open to discussion from the conference. Some of the thoughts behind some of the recommendations are also discussed.

The MOT Report was favourably received when first published. However there has been some criticism. The purpose of the paper is to allow members to voice their difficulties, and by mutual exchange of views, to solve them.

I. Critics assert that the Report fails as it does not evaluate street lighting installations because it does not provide a measure-rod by which installations can be assessed with precision, and weighed against another. However there was nothing in the terms of reference about providing "yard-sticks." Also the various editions of hte British Standard Specification have never been accepted as infaliable measures of hte merits of installations. Indeed the 1931 Specification clearly disclaims any such purpose.

II. Why only two classifications of road? All witnesses said that at the present time there is an unfortunate lack of uniformity of lighting throughout the country. Not only a want of uniformity in standards of illumination but in the arrangement of the lamps, in their spacing, their power, their mounting height etc. This was most confusing to motorists, who were constantly in doubt as to whether the street lighting provided enabled them, or was intended to enable them, to extinguish the headlights of their vehicles.. It would've been easy to say that the standard of lighting to be provided in the future in all built-up areas should be such to give visual safety without the use of headlights. Such advice would have been quite impractical, and would have resulted, I fear in nothing being done at all. Many difficult lighting schemes were considered but it was decided to use the simplest classification of roads i.e. "Traffic Routes" and "all other roads."

III. When should headlights be extinguished. Lighting of "Traffic Routes" would be such to render the use of headlights unneccessary. It was a matter of importance that drivers should be free from uncertainty over the use of headlights, and it was felt that there should be a definite gap between the two ranges of lighting. The distinction is brought about in two ways:

• The mounting height of the light sources. 25' presents no practical difficulties in most cases.
• The quantity of light provided.

• Low pressure gas using 500 B.Th.U gas should give 160-200 lumens per cu. ft. of gas.
• High pressure gas should give 280-300 lumens per cu. ft. of gas.
• Take the specified light output over life of electric lamps and deduct 30% for absorption of reflectors/refractors.

V. What would be the effect of the universal adoption of the Report throughout the country?

• Traffic routes: units mounted at 25', 3000-8000 lumens per 100' of road (with a carriageway of not more than 40') and the use of headlights unnecessary.
• All other roads: units mounted at 13'-15', 600-2500 lumens per 100' of road, use of headlights optional. (Those familiar with the locality would be able to turn off their headlights if conditions allowed).

VI. Traffic Routes The spacing is too close. For traffic routes, spacings greater than 150' are intended to be exceptional: such close spacing makes it easier to deal with junctions, intersections and irregularities of road formation and close spacing has a bearing on the elimination of glare. The overhang is too large. For traffic routes, the maximum distance between the two rows of sources should not exceed 30', for a dark centre of the road to be avoided. (Therefore with a road width of 40', the overhang should be 5'). There was some conflict on the siting of lamps. Some witnesses expressed a preference for central suspension, but most witnesses disagreed. It was stated, for example, that central suspension rendered it difficult to provide adequate visibility near the kerb and on the footway, especially on wet roads, and that it induced traffic to keep to the crown of the road. All witnesses agreed that confining the lamps to one side of the road on straight stretches results in defective lighting.

It is said that paragraph 46 is not precise enough. For greater precision, this will have to wait for the British Standard Specificaiton. The guiding principle in all questions of siting is that there should be a light source in such a prosition as to produce a bright background to any object with which the driver may be concerned. To get these results, its recommended that lamps should be placed on the outside of the road curve - the angle of separation from 200' of the observer should be 3.5°.

The spacing will be in some cases irregular - particularly at intersections and bends - so should the power of the light sources be graded so that the luminous output per 100' linear be constant? There is nothing in the Report to prevent this, but it is not recommended. The additional volumne of light, because of the closer spacing, is all to the good.

It is impossible to lay down rules which can be universally applied to roundabouts because they vary:

• In their formation
• In their dimensions
• In the angles with which approach roads converge on the area.
• In the reflection and other characteristics of the surroundings.

Witnesses were unanimous in condemning the practice of endeavouring to make up for a far too large space-height ratio by using a type of fitting which sends out a highly concentrated beam of light at angles close to the horizontal. Long spacing and high concentration of the main beam were two evils which do not cancel out.

VII. Effect Of The Nature And Condition Of The Road Surface It is difficult to light a road surface which exhibits variations of colour and texture. A surface should be provided and maintained which is as uniform as possible. Light coloured kerbs are helpful from a lighting point of view.

VIII. Dual Carriageways It is felt that the limited experience of the lighting of such carriageways does not permit of definite recommendations being made but the tenative suggestion is made that dual carriageways should be lighted as separate Traffic Routes.

Where the carriageways are more than 30' in width, or where the central reservation is more than 10' in width, each carriageway should be lighted independently as a separate Traffic Route.

Where the carriageway is 30' or less in width, and where the central reservation is 10' of less, lanterns mounted over the central reservation may be considered as contributing to the lighting of both carriageways.

IX. Lighting Of Group 'B' Roads The general rules applying to the lighting of Traffic Routes apply also to the lighting of residential roads.

X. Maintenance: Satisfactory maintenance is just as important as correct design. Illumination measurements by virtue of their relative simplicity provide a practical means of assessing the state of maintenance.

• The daylight appearance of the street lighting plant should be kept in mind and cleaned to ensure good daytime appearance.
• Inpsection should be made from time-to-time to make sure they're in their correct positions.
• The settings of reflectors/refractors should be checked.
• Gas burners should be cleaned frequently
• Electric lamps hsould not be allowed to burn beyond their useful life.

The Report is not intended as a Specification, and the view is expressed that the recommendations made should be implemented, with a minimum of delay, by the issue of a formal Specification by the British Standards Institute.

XI. It is recommended that consideration be given to the responsibility for the lighting of classified roads being confined to large administrative units. Grants should be provided from National Funds.

Mr. Thos Wilkie
(Public Lighting Engineer, Leicester)

Keywords: Lighting: ARP and Lighting: Control

Tuesday, September 6th, 1938

Summary and discussion published in: Public Lighting, Vol. 3, No. 11. September 1938

Abstract: After black-out experiments in Leceister early in 1938, Wilkie outlines the arrangements made to achieve black-out and the lessons learned from the experiment. The Home Office Circular outlining the potential plans for black-out, issued after the experiment, is also discussed. However Wilkie argues strongly for the study and provision of centrally controlled lighting schemes, and points out the many advantages of avoiding a total continuous black-out.

The object of the paper is to set down reasons why a state of continuous darkness cannot be looked upon with equanimity. The method of achieving this is by means of some type of control system. It is felt that it would be possible to entrust this important control of lighting to one, or more, of these systems. It is assured that the only motive behind the paper is to suggest points which may not have been considered by those in authority.

I am firmly of the opinion that the provision of lighting during non-raid periods will make a quite considerable constribution towards reducing the rigours of war.

Experience was gained from black-out experiments which took place in Leicester earlier in the year. First the arrangements will be discussed and then the lessons learnt will be outlined. The experiment was not intended to ascertain how short a period a large city could be darkened bur rather, having achieved darkness, to test methods of aiding movement of essential traffic in these darkened streets.

The experiment took place from 1AM to 3AM on 28th January 1938. There was no moon and during the first hour the weather was dry, but at about 2AM rain commenced to fall. The rain proved of value since it gave two complete sets of conditions. Certain streets in the city were chosen for the actual driving exercise and 200 special constables diverted all traffic from the pre-arranged routes. The time taken to darken Leicester for the experiment was between 1¼ and 1½ hours.

Hand Lit Gas Lamps: Each lamplighter was ordered to extinguish the lamps at such time that his last lamp would be dealt with by 12:45AM. After the exercise, at 3AM, all lamps were relit.

Controllers And Time Switches: This was more difficult. The time the lamps to be extingushed was reduced to 12:30AM. Two full days prior to the black-out, each attendant commenced to reset every third lamp to extinguish at 12:30AM, the following day he reset another third, and on the last day he reset the last third. After 3AM, the lasst day's lamps were brought in by hand and reset for normal extinguishing during the following day. The remaining lamps were reset as soon as possible.

Main Roads (Tramway Routes): By means of my own system of control, most of the main road lamps were extinguished from the main road in 86 seconds. (One contactor behaved badly and did not disconnect for 10 minutes). "Keep Left" bollards, one-way signs etc., were not controlled from the head office and were individually reset on the day of the exercise. At each island the normal "Keep Left" signs were darkened and hurricance lamps with specially made spill shields were placed.

Traffic Light Signals: Ordinary intensities were retained, but each lens was covered by metal discs or impenetrable black paper. In spite of the tremendously reduced area showing to traffic, there was not a single vote cast against this treatment.

"Keep Left" Bollards: Metal louvres were fitted to each aspect except that facing towards the centre of the island, which was blacked out by tin. All the louvres were painted matt black as was also the spill shield on the top. 5W lamps were used, sprayed red or parchment colour. Without exception, every driver and observer voted the result "quite satisfactory."

Lighthouses: These had the tops painted with black paint, the four traffic windows were covered with thin paper, a large spill shield was fitted, painted black, and red sprayed 5W lamps fitted.

Portable Bollards: These were sent from Scotland Yard for incorporation in these Home Office tests and were very effective.

Motor Side, Tail And Head Lamps: Normal car lighting was drastically dealt with. Illumination curves were taken of the normal 12V 36W head-lamp, and the same head-lamp fitted with the Home Office mask. The experiment showed that very low intensities were permissible under darkened conditions. (In a later experiment in Glasgow, head-lamp masks were again used but would appear to be a different pattern.

The test streets were divided into sections, and each section was treated in a different manner as regards aids to driving, in accordance with the wishes of the Home Office. There were 18 sections with various white paint lines, reflectors, painted kerbs, trees with white bands, tramway and lighting poles with black and white painted stripes, and unmodified. The commencement of each section wsa indicated by means of specially made lanterns using white alphabetical letters on a black field.

The experiment did produce definite opinions. Detailed reports were received, embracing the opinions of 59 actual drivers and observers over the whole of the test road, measuring 6.7 miles. They were asked to indicate likes and dislikes which showed very decided agreement over which was best and which was worst. (The deciding factor for "best" was the centre white line).

Reflectors did not receive much support but this was probably due to their positioning. There were two main reasons why they were not as effective as they might have been :

• Reflectors rely on light falling upon them, but owing to the use of headlight masks, then little light reached them.
• There should be some relation between road width and the angle of the reflector face.

The Leicester experiment could be challenged on four grounds:

• Every driver was thoroughly acquainted with the test route.
• He knew the various road-markings beforehand.
• There were no pedestrians using the streets under test.
• He was accompanied by an observer who also assisted in navigation.

• Normal street-lighting would not be permitted in time of war.
• Adequate means of aiding movement in darkened streets would accordingly be required in all streets likely to carry considerable traffic.
• Reflectors, white markings, or dim, well-screened indicator lights which cast no appreciable illumination but served merely to show their position would be used to mark the line of the road and also obstructions and danger points. More precise particulars of 'aids to movement' of this kind will be supplied as soon as possible.
• Traffic control signals, fitted with approved masking devices, would be allowed to remain in operation in darkened streets.
• It is not thought that further experience will reveal the need for any modification to these proposals. If any relaxation were found to be necessary, it would not go beyond permitting between raids a certain amount of modified street-lighting, carefully screened and capable of being instantly extinguished on receipt of an air raid warning, in the main thoroughfares of the largest towns, and then probably only in the less exposed parts of the country.

The Circular indicates that no known control system for street lighting is good enough to be generally entrusted with street lighting, but I feel that it is not impossible to find an acceptable system. Lighting should be allowed during normal dark hours and that, when a raid is imminent, all lighting should be extinguished until the "all-clear" is given, when lighting should be restored. The following are the reasons for that viewpoint:

Precision Of Night-Flying: This has improved greatly since the last war. Therefore full black out may not be necessary.

Purpose Of Air-Raids: The purpose over airs which are not military operations is:

• To dislocate or destroy works of national importance. Therefore they should be made as inconspicuous as possible but this may not be achievable in every case.
• To destroy civilian morale. This represents a high percentage of inhabited areas and target precision is unnecessary.

Vulnerability Of London: For lighting, a case could be made for complete continuous darkness in the East Coastal areas. But such restrictions should not be made automatically to inland or West Coastal areas. Likewise there are many cities which, even in complete darkness, would be found by virtue of their proximity to rivers.

Furnaces And Munition Works: If it is accepted that a state of universal darkness is necessary, this will be rendered negative by such works.

Incendiary Bombs: These represent another agency which will work against the safety which it is hoped to create by the imposition of drastic lighting restrictions.

Darkening And Relighting: The present accepted method of warning civilians that an air-raid is imminent is by the use of sirens but darkening a city would be an extremely useful and effective auxiliary to the sirens. But the act of re-lighting, when the "all-clear" is given would be invaluable in restoring the morale of inhabitants.

After A Raid: If lighting could be restored when the "all-clear" is given, then work would be more effective e.g.g rescue work, decontamination etc. Restoration of lighting would also be of tremendous value to Fire Brigades and Ambulances.

Crime: During a prolonged period of darkness it would be difficult to control crime.

General Objects To Darkness: Social habits have changed since the Great War. There are a larger number of pedestrians out at night. The vital need of the moment, from every point of view, is for a system, or principle, of control which would be sufficiently effecient to satisfy those in authority. There are many systems available, some which have been in practical operation for quite a long time. If these known systems are not perfect enough, further examination and experiment should be proceeded with. The initiative should be taken by the Home Office. Without a control system it will be quite impossible to darken a city in less than six hours.

Considerable numbers of additional lamps are being erected and a large percentage of these will be equipped with a time-switch. If a control system was used, all new installations could be initially equipped with the means of instantaneous extinguishment. The peace-time labour costs of operating such a scheme would be considerably lower than the normal method. But the real advantages would be in war-time. In addition to providing very intimate control between raids, the system would be an integral part of the ARP scheme. It would be capable of:

• Street lamps out.
• Operate warning sirens.
• Street wardens out.
• Fire wardens out.
• Call fire brigades.
• Call ambulances.
• Decontamination squads.
• Sound "All Clear" sirens.
• Street lamps on.

Mr. W. Hodkinson
The United Kingdom Gas Corporation

Keywords: Lighting: ARP, Lighting: Authority Organisation, Lighting: Control, Lighting: Funding, Lighting: Installations, Lighting: Luminaires and Lighting: Specifications

Wednesday, September 7th, 1938

Summary and discussion published in: Public Lighting, Vol. 3, No. 11. September 1938

Abstract: Describes in detail some of the installations erected in the last three years for the Constituent Companies of the United Kingdom Gas Corporation. The paper refers to several aspects of public lighting problems which have been brought to their notice and which prove of general interest. Descriptions are given of installations erected with details of the installation, the roadway, photographs and iso-foot-candle diagrams. All aspects of gas installations are covered including installation, maintenance, new developments, the MOT Report and forthcoming ARP measures. The conclusion is that gas for public lighting service is still a sound proposition and research has not ceased and further progress in efficiency and service is expected.

The United Kingdom Gas Corporation controls a total of 66 Gas Undertakings. During the past three years, this office has assisted the Constituent Companies in the preparation of numerous public lighting schemes in numerous small towns and villages throughout the country. It is quite obvious that considerable diversion of opinion exists amongst experts concerning the basic principles of the street lighting problem, and to add further confusion, we find ourselves with an obsolete specification and a scheme of recommendations without any leading specification. The merit of a street lighting installation must be evaluated in terms of ease and effectiveness of visibility but the only way to achieve this is to examine the installation at work on the road it is to serve and under the varying conditions it has to meet.

Having this point in mind, we have adopted the practice of offering to provide and erect free of charge and without obligation, demonstration installations of not less than six lamps in the road to be lighted. We are quite satisfied that this is the only effective method of indicating to the Authority concerned what results they will obtain from the installation.

Main Traffic Road Lighting: The lighting of Denton, Lancashire; Ormskirk, Lancashire; and Morley, Yorkshire is described. We are satisfied that gas can still do a good job of work in the illumination of main arterial roads, and this opinion is confirmed by the amount of new business which we are obtaining in this direction.

Illuminated Guard Posts: Gas as a source of illumination for road signs and guard-posts has within recent years gained the support of a number of local authorities. There has been criticism of the use of gas for this work that in the event of a knock down, the escaping gas may result in fire and injury. As a precaution, a special valve designed to cut off the gas supply if the pipe is broken, as been devised by the Gas Light And Coke Compay, and manufactured by Sugg. (Description and diagram of the unit is given which uses two pipes, an internal valve driven by a pressure-actuated diaphragm and a "weak link").

Side Road Lighting: An examination of the literature relating to Street Lighting published over the last four or five years reveals the amazing fact that practically no attention has been paided to the importance of the illumination of side roads. It is generally provided for the comfort and safety of the general public. It has been proved that adequate lighting is the most successful deterrent to crime. The scope is invariably limited by the question of costs. I am of the opinion that even distribution of illumination leading to silhouette vision is the most important factor to be considered.

In several recent schemes Sideway or 8000 types of lamp are used. In Yorkshire, 4-light No. 2 size Sideway units fitted with constant pressure governor, Newbridge Clock Controller and automatic Comet igniters were used. Mounting height was 13'6", spacing (staggered) 120' with a road width of 22'.

Suspended lamps are also used and the Rochester, Arcturus and Stechford lamps are used in installations. In a recent installation, they used 6-light No. 2 upright suspended Arcturus lamps from Foster And Pullen, mounted on steel poles, and were fitted with constant pressure governors, Newbridge Clock Controllers and Comet igniters. The controller and igniters were fited in a neat cast iron box positioned centrally to the two upright suspension arms. Mounting height was 15', spacing (staggered) 120' and the width of the road was 24'. The light ouput was 2500 lumens per 100 ft. linear.

Square lanterns are also used despite being considered old fashioned and out-of-date. If of sufficient capacity and sited in accordance with modern requirements, they can still perform an excellent job. The lighting of Rothwell is described.

Improvements To Existing Installations: Many small local authorities have adopted the policy of systematically improving existing installations with a minimum of capital expenditure by increasing lamp capacities and providing modern reflecting or refracting appartus and automatic control. An example: 2-light No. 2 size mantle, 16" square lanterns mounted on cast-iron column ata height of 10'6" were stripped and overhauled and fitted with 3-light No. 2 size mantle superheater burners, stainless steel reflectors and clock controllers containing automatic ignition. The columns were raised by the use of extension pieces to provide a height of 14'and moved so a staggered formation was possible. The savings effected in labour charges and gas consumption by the use of automatic control and modern high efficiency burner equipment were sufficient to cover the cost of increased light output nad provide a substantial contribution to the interest charges on the capital expenditure.

The Minstry Of Transport Report: At present, conformation to the Report is too expensive. Small towns can only view the Report as an interesting publication (for both Group A and Group B lighting). Small councils cannot raise the capital through their rates. It is quite obvious that some assistance must be provided for the majority of small towns and villages in this country to enable them to enjoy the advantages and safety of modern standards of public lighting. The most serious aspect of this problem is that where local authorities find themselves unable to adopt the recommendation contained in the Report, they become reluctant to undertake any improvements to their lighting, preferring to conserve their spending powers in the hope that at some future date assistance will be provided to enable them to adopt the Ministry's recommendations.

Maintenance And Service: Gas as a source of public lighting is quite often considered out-of-date and unable to keep pace with modern requirements. This is to some extent deserved, but the whole of the blame can be traced to poor maintenance. During the past 10 years intensive research has produced the equipment which can place gas in the front rank as a lighting medium. The Gas Industry today realises the vital necessity of service. We are no longer content to sell gas for lighting, but we are determined to sell a lighting service which we believe has many inherent advantages. A small seaside town lit by 300 gas lamps was lighted and maintained by one man with the occasional assistant of a youth: the recommendation was that the Authority should place the whole of the responsibility of lighting with the Gas Undertaking and that Public Lighting Engineers should be shared between authorities. Designs of modern gas lamps pay attention to the necessity of the ease of maintenance and constancy of light output (by pressure governors and fixed injector orifices). All these modern developments have assisted in reducing maintenance costs and allow Gas Undertakings to provide a very high standard of maintenance at a reasonable cost.

Automatic Ignition: The development of automatic ignition has proved a considerable aid to service. The Horstmann Comet type igniter is used in conjunciton with their quick-action clock controllers. The advantages are:

• Economy: Bye-pas consumption is 0.25 c.ft. of gas per hour. The Comet igniter uses not more than 1 cu.ft. per season.
• Reliability: The igniter provides a very generous flame and it is impossible for this to be blown out during the short time it is doing its work. The igniter is actually only emitting a flame for about 30 minutes per year.
• Reduced Costs.

Light Actuated Control For Gas Lamps: The MOT Report recommends that street lighting should be continued during the hours of darknes and not as heretofore by a prearranged time table. A recent development for gas street lighting is the use of a photo-electric cell. This appartaus was devised by the South Metropolitan Gas Company and was adapted with the Gas Light And Coke Company for use with street lighting. (For description see South Metropolitan Gas Company.) The Council who first had this method of control installed was so pleased that several repeat orders have been made. The running costs are practially negligible.

Air-Raid Precautions: Without some definite guide it is impossible to budget for this eventuality. Many authorities have formed the opinion that where gas is used as a source of light, prompt extinction cannot be effected. Some experimental units have been made, which are a simple cut-off valve, operated by either an increase or decrease in gas pressure. The valve will remain closed until operated manually.

Luminaires: Sugg London, Parkinson Maxill, Foster And Pullen Alpha, Foster And Pullen Sideway, Sugg 8000, Sugg Rochester, Foster And Pullen Arctutus Parkinson Stechford and Foster And Pullen Avil (assumed to the the Standard).

Mr. J. K. Brydges, M.I.E.E. and Mr. N. Boydell, A.M.I.E.E.

Keywords: Lighting: Colour, Lighting: Columns, Lighting: Control, Lighting: Environment, Lighting: History and Lighting: Installations

Wednesday, September 7th, 1938

Summary and discussion published in: Public Lighting, Vol. 3, No. 11. September 1938

Abstract: History and description of the lighting of Eastbourne. Future plans are also outlined.

The details of Eastbourne's lighting from this paper is covered in the installation section.

Luminaires: Gilbert Arc-Lamp and Reason G. (Modern luminaires are described but manufacturer details are not given).

Mr. J. N. Aldington, B.Sc., A.I.C., F.Inst.P

Keywords: Lighting: Lamps

Thursday, September 8th, 1938

Summary and discussion published in: Public Lighting, Vol. 3, No. 11. September 1938

Abstract: "All artifical illuminants radiate energy over a considerably greater range of frequences than the eye can appreciate. Improvements in efficiency are, therefore, obtained by increasing the proportion of radiant energy within that band of frequencies to which the retina of the eye resonds."

"In the case of incandescent radiators the desired effect is produced progressively with increasing temperature, and improvements in incandescent lamps have been effected by making use of this phenomenon."

"There are greater possibilities with electric discharge lamps. The mercury lamp, in particular, offers scope and flexibility; development is still proceeding."

"Is it too much to hope that the progress so far achieved has but shown the pathway to still unexplored regions?"

The efficiency of an illuminant is dependent on the percentage of its total radiant power which is emitted in the comparatively limited region to which the eye is responsive. More power will be necessary to produce equal visibility from the red or violet ends of the spectrum than will be required from the green region. "The retina is excited most effectively by radiation of about 5,550A. It is stimulated to a decreasing extent by energy in a waveband extending to about 1500A on either side of this maximum, and not at all by energy outside that limited range." A light source having a well balanced spectrum akin to that of daylight, will necesary be less efficient than a source of equal energy whose output is concentrated in the yellow region of the spectrum at 5,550A. Therefore a yellow-green light would be most effective and the dissipation of one watt of energy at 5,550A would result in the production of 621 lumens.

The relative low values of luminious efficiency associated with modern lamps is due to only a small amount of flux radiated in the visible region.

Incandescent Illuminants
Until a short time ago the only practical method of producing light was that of incandescence. When a substance is heated above a certain temperature, it produces light, and that the higher the temperature, the brighter and more efficient the incandescent illuminant. Most substances undergo similar colour changes at approximately the same temperature, they emit radiation having the character of a continuous spectrum (the properties of which are a function of the temperature) and at any given temperature they radiate a similar proportion of their energy in the visible region.

These characteristics approximate to those of a non-selective radiator which is a body or substance at a uniform temperature, radiated energy under such conditions that the radiation at every wavelength is the maximum possible at the given temperature, and is dependent only on that temperature.

As luminous effeciency is determined by the ratio of the power radiated in the visible region, to the total power, then we would not anticipate a high efficiency from a non-selcted radiator at 2000K. The effect of increasing the temperature of the radiator is to move the energy maximum in a helpful direction. Not only does the total radiant power increase with increasing temperature, but relatively more energy is radiated in the visible region. At 6500K the power radiated would be a maximum. However, there is no element wich will act as a solid radiator at such extremely high temperatures. Progress in the development of incandescent illuminants have been directed towards the production of radiant materials capable of being operated for long periods at the highest possible temperatures.

The Flame
A hydrocarbon flame dependent on chemical combustion e.g. the candle, the oil lamp, the paraffin burner and the gas flame. It involves the oxidation of the hydrocarbon to carbon dioxide and water vapour and produces temperatures of 2000°K. The flame luminosity is due to the incandescence of minute particles of carbon resulting from the incomplete oxidation of the hydrocarbon. The study of the the mechanism of this type of incandescence paved the way for the introduction of a spearate radiator raised to a high temperature by contact with the flame itself. When first introduced the gas flame was operated with a limited amount of air; later, a higher temperature non-luminous flame was produced by pre-mixing the coal gas with air as in the well-known bunsen burner. The developement of the Welsbach Mantle which incandesces by contact with the high temperature zone of the bunsen flame made possible much higher efficiences of light production, and began a new era in lighting by gas.

The Welsbach Mantle
Consisting of a light porous structure of thoria with 1% ceria, the Welsbach Mantle is generally of a cylindrical form with a spherically closed end. It attains a temperature several hundreds of degress higher than that of a thin metallic wire placed in the same flame. In the visible spectrum the thoria-ceria mixture has a high emissivity while in the near infra-red it has a much less emissivity than a black body in the same temperature. In the far intra-red region its emissivity rises again; therefore it is an example of a selective radiatior. The oxides used in its preparation radiate preferentially in the yellow-green region of the spectrum.

Incandescence Produced By Electric Current
The electric arc lamp, the Nernst Glower and the incandescent filament lamp are examples of this method. The most important is the filament lamp, not only on account of its simplicity, but because of its flexibility of application.

The Incandescent Electric Lamp
The early history of the filament lamp was dominated by the search for the most suitable radiator, capable of carrying an electric current and being operated at the highest possible temperature. Progessively these were carbon, osmium, tantalum and tungsten.

Tungsten (with the exception of carbon) has the highest melting point. It can run in excess of 2500°K. Yet it is the evaporation of the filament which finally determines the life of a lamp. Any means which will cause a reduction in the rate of evaporation will obviously enable a filament to be operated at a higher temperature for a given life and therefore a higher efficiency. Such a means was made available when Langmuir showed how a filling of inert gas in the lamp envelope could be used to reduce the rate of filament evaporation. The coiling of the filament diminishes the surface exposed at the gas interface and therby reduces heat losses to a minimum. The development of the gasfilled lamp thus enabled the filament to be operated at a higher temperature than was possible in the vacuum lamp for a give life, and led to the attainment of higher luminous efficiences.

The specification (BSS 161:1937) calls for an average life of 1000 hours and it is significant that for lamps having the same life performance the efficiency increases rapidly as the wattage increases. The higher designed efficiencies of the higher wattage lamps result for the almost obvious property that the thicker the filament the greater will be the amount of evaporation which it can undergo before failure, and consequently the higher the temperature at which it can be operated for a given life. The higher temperature of large wattage lamps gives a more benefical distribution of energy in relation to the visible spectrum.

Another very successful step was the introduction of the coiled-coil filament. Yets of patient research were necessary to produce tungsten wire of such stability that it could be fabricated into the coiled coil and yet preserve its original contour. A coiled coil lamp of 40W has an increased efficiency 20% greater than the single coil lamp. The increased efficiency results from a reduction in the amount of energy transferred to the gas in the lamp by convention currents.

The theoretical limit is 50 lumen/watt which represents the efficiency of a tunsgten filament lamp operating at its melting point.

The Production Of Radiation From Electrically Excited Atoms
The radiation from an electric discharge lamp is emitted mainly at specific frequencies dependent on the gas or vapour under excitation. A high luminious efficiency results, particularly if the wavelengths are near the centre of the visible spectrum. In some cases, the excited vapour emits energy in both the visible and ultra-violet regions so that methods can be used to improve the colour rendering. Radiation produced by the direct excitation of atoms is known as primary radiation. Secondary effects are produced when other atoms absorb the primary radition and re-emit the energy at either the same wavlength (resonance) or at some other, generally longer, wavelength.

Ofthe 92 elements, only a very few have been used as light sources in electric discharge lamps. Some are incapable of vaporisation at reasonable temperatures and others are too chemically reactive. Of hte remainder, many are unsuitable becuase they emit only a relatively small amount of energy in the visible region.

The Radiation From The Sodium Lamp
Experimenntally, in special laboratory lamps, efficiences as high as 200 lumens per watt have been attained. In commerical lamps, the heat generated by the discharge must be sufficient to maintain the temperature of the lamp and the sodium vapour pressure at the required value; tbe current density has thus to be suitably related to the lamp dimensions. The conditions which determine the production of the primary or resonance radition from the sodium atom, are minimum current density and minimum concentration of sodium atom. Both these conditions suggest a considerable lamp size for a given wattage.

The difference between the commerical values of efficiency and the theoretical possible is due to part of the energy being converted to heat to maintain the lamp at the necessary temperature of 280° at which the concentration of sodium vapour is more benficial. Heat losses are kept to a minimum by the double walled envelope enclosing the discharge tube. The effect of loading a sodium vapour lamp would cause a reduction in the efficiency. This result is due to complex processes involving the absorption of some of the primary radiation and the production of infra-red radition. The possibility of producing sodium lamps emitted other than a practically monochromatic yellow light is not very feasible. Improvements must be sought in the direction of increased effciencies due to obtaining a more effective transfer of electrical energy into radiant energy at 5890A - 5896A. This radiation lies practically at the peak of the eye sensitivity curve: this determines the yellow colour of sodium light and has an important bearing on the high luminous efficiences which can be obtained.

The conditions which produce the optimum luminous efficiency from a sodium lamp are low current density in conjunction which a very low vapour pressure of the metal.

The Radiation From Mercury Discharge Lamps
The resonance radiation from mercury occurs at 2537A in the far ultra-violet region. However, with increased current density and higher vapour pressure, the mercury vapour lamp can be made a highly efficient radiator in the visible region. The flexibility of development possible in the case of mercury vapour lamps is partially due to the fact that the relative intensities of its spectral lines may be varied by changes in the pressure at which the mercury vapour is allowed to operate.

As the mercury vapour pressure increases, the efficiency in lumens per watt increases; however the change in pressure from a fraction of a millimetre to about one atomsphere produces the largest increment in efficiency.

Increases in pressure cause the lines of longer wavelengths at 5461A, 5770A and 5790A to be preferentially excited - this accounts for the high luminious efficiences obtained at the higher pressures.

Fluorescent Lamps
In the case of the 400W high pressure mercury lamp used for street lighting the dominant wavelengths are in the yellow, green and violet; the light is deficient in the blue, orange and red regions. These can be added by means of fluorescence.^[1] Employing a stable coating of fluorescent material on the inner surface of specially designed outer bulbs, these lamps have inner tubes containing a mixture of cadmium and mercury. The fluorescent powder strongly absorbs radiation in the near ultra violet amd transforms this energy into broad bands or radoant energy in the orange-red. Powders are now available which fluoresce with practically every shade of colour^[2] but not all these are suitable used with the high pressure mercury lamp (some are not active as the temperatures used, and some are not stable).

The most striking use of fluorescence is that in which various powders are coated on the inside of low pressure mercury discharge tubes i.e. fluorescent tubes. Of very low power consumption, these tubes are being produced experimentally for interior illumination:

• The luminious radiation from the mercury is extremely low, most of the energy being in the ultra-violet region, which strongly excites the special powders now available.
• Fluorescent materials, capable of being excited by direct contact with low pressure mercury discharge, are available in a wide range of colours.
• Compound powders are possible which have a continuous response over the whole visible spectrum.

The efficiences are from 30-40L/W with a consumption of the order of 25W in a tube about one metre in length.

Higher Pressure Mercury Discharge Lamps
First described in ^[4] and ^[5]. It was shown how 80W and 125W lamps, operating at higher pressures than the 400W type, had improved colour and a greater proportion of both blue and red light. Excitation of mercury atoms, under conditions of high pressure and temperature, is beneficial not only for luminous efficiency by from colour. [These became known as MB lamps].

At still higher temperatures and pressures, the favourable effect is even more marked. The luminosity curves from a 500W ME lamp give radiation approaching the quality of daylight. High brightness air-cooled ME lamps are being developed for projection work. The arc is formed in a specially shaped quartz bulb. The current leads are sealed through the quartz by the method mentioned in ^[5], which has been extended to allow currents as high as 100A.

Brightness Distribution In High Pressure Mercury Lamps
For certain purposes it is useful to have some knowledge of the distribution of brightness in the light source itself. The luminosity of the central core of the discharge is not distributed evenly across the width of the arc, being greatest at the centre and falling off towards the edges. It is the high peak brightness and small arc dimensions of the ME lamp which make it so suitable for projection work. There are other indications that the possible uses of electrically excited mercury vapour as a source of luminous radiation are by no means exhausted.

References:
[1] The Application of Modern Electric Lamps to Street Lighting, Mr. G. H. Wilson B.Sc. (Eng.), A.M.I.E.E., A.P.L.E., Folkestone, 1937
[2] J. W. Ryde, Ill. Eng. Soc., April 1938.
[3] J. T. Randall, Porc. Phys. Soc., Vol. 49, 1937.
[4] The Electric Discharge Lamp - A Survey Of Development, J. N. Aldington, B.Sc., A.I.C., A.P.L.E., Cheltenham, 1936
[5] The Application of Modern Electric Lamps to Street Lighting, Mr. G. H. Wilson B.Sc. (Eng.), A.M.I.E.E., A.P.L.E., Folkestone, 1937