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ilp archive : journals

public lighting no. 16 vol. 5
January 1940

Editorial p5
Sir John Anderson, Minister of Home Security, was interviewed on the radio on the 15th December 1939 on the subject of street lighting. He paided compliments to the APLE. As a result of efforts, the whole country, with the exception of certain vulnerable areas, is to be given a slight relaxation from the oppressive gloom of the previous four months. There had been much criticism from all quarters about the "black-out." Much work had been done by the Joint Lighting Committee, which included members of the APLE, in carrying out exhaustive experimetns to evolve some form of lighting that would overcome complete darkness, yet of such low intensity to remain invisible to enemy aircraft. At a recent meeting of the APLE, confirmed there was no easy way out, but the problem could be partially solved by the scientific use of low intensity lighting of the type recommended by the Joint Lighting Committee. Sir John Anderson remarked "After many experiments, tested by the RAF from the air, this problem has now been solved, with the assistance of the lighting engineers." Except for certain areas on the coast, the new form of lighting is to be permitted all over the country.

The Late Hugh W. Gregory, M.I.M.E. p5
Obituary of Huge W. Welbourn Gregory who had just been elected Vice-President of the APLE during the December conference.
Lighting: Personnel

Street Lighting Introduced p6
For several months, experiments have been proceeding in all parts of the country on the lighting of streets in the black out. The BSI has now issued a specification for a unit to be used for this purpose. On the 14th December 1938, the new standard of diffused light allowable - 0.0002 foot candles - was demonstrated to the press and members of the I.M.E.A., when two miles of main road in North London and half a square mile of adjoining suburb were lit following St. John Anderson's announcement in the house. This lighting is caleld "comfort lighting": it gives sufficience illumination for pedestrians to avoid pavement obstacles. It is not intended to make the way clear for motorists - it was not possible to provide sufficient light without constituting danger of attack from the air. The lighting can be left in operation during an air raid. The delays in introducing this lighting has caused much complaint and discomfort to the public.
Lighting: ARP, Lighting: Levels, Lighting: Specifications, Lighting: Theory

The Sixteenth Annual General Meeting p7
The meeting was held at St. Ermin's Hotel, London on the 28th November. Mr. E. J. Stewart. M.A., B.Sc. (Glasgow) was elected President for 1939-1940. The conference brochure and papers for the postponed Glagow conference had been printed, and were to be put in cold storage. It was informally decided to hold the next full conference in Glasgow. Public Lighting and the Annual Report would be continued. The idea of regional meetings to discuss expert problems in connection with the "black out" were discussed: the Home Office's representative Mr. C. W. Johnson was at the meeting can could be asked questions; region meetings had been held in the north jointly with the Illuminating Engineering Society; but it was considered that regional meetings were a very good idea and would be discussed by council. The question of professional status and technical examinations was also discussed: those who had passed their City And Guilds could be admitted although they would not be full members, but would have a status - a full member was a representative of a local authority.
APLE: Conference, APLE: Journal, APLE: Organisation, Lighting: ARP

Street Lighting In Australia p9
There has been issued by the Standards Association Of Australia a Code to meet the need for some authoritative recommendations regarding the requirements considered to be necessary to bring street lighting in Australia to a higher level of efficiency. In preparation of the Code, the Final Report of the MOT, the specification for Street Lighting by the BSI and the code of Street Lighting used by the Illuminating Engineering Society (USA) were all studied. Experimental lighting installations were established by two large electricity supply authorities. In general, the Code deals only with the minimum requirements for the satisfactory lighting of streets and is applicable to both electricity and gas. The new publication (C.A. 19-1939) contains sections dealing with the purpose of street lighting, provision for discernment and means of specifying street lighting, classification of streets, spacing, mounting height, lumens per linear foot, one-way streets, types of unit and brightness and glare.
Lighting: Specifications

The B.T.H. A.R.P. Street Lighting Lantern p9
The upper and lower limits of lantern light distribution imposed by the specification (BS/ARP 37) require a precision design of lantern. B.T.H. have designed and produced a lantern, bearing the hallmark of the the B.S.I., depending on its precision and permanence of performance on the use of die-cast parts, which are accurate to a thousandth of an inch, and cannot be deranged or distorted. The slaient features of these lanterns are:
  • Easy Erection: It can be supplied completely assembled and wired to its own adaptor for screwing into existing lamp sockets. or alternatively threaded 1½ B.S.P. for screwing direct on to the bracket arm.
  • Simple Cleaning: Access can readily be obtained to every optical component.
  • Minimum Of Servicing: No adjustments are necessary at any time to allow for normal tolerances in light centre lengths of lamps.
  • Freedom From Glare: The distribution is produced from secondary sources of low brightness. The bare lamp is not visible from any point of view.
Lighting: ARP, Lighting: Luminaires

Publications Of Interest To Lighting Engineers p10
The Story Of Town Gas by the British Commerical Gas Association. This brochure describes in simple language some of the ways the Gas Industry affects business and industrial concerns.
Light In Daily Life by J. Stewart Dow, B.Sc.. Contains a series of articles dealing with the history and progress of artificial lighting. In Dow's opinion, there is need for the appointmetn of a whole-time lighting official in all important towns and cities.
Wiring Sundries, etc. by the GEC. A new edition of the catalogue dealing with insulators, insulating materials, dynamo and instrument wires, tools and other installation apparatus.
Mercury And Sodium Lamps by Ediswan. Contains useful information on the construction and erection of the firm's Royal "Ediswan" Escura Lamps.
Public Lighting By Gas by Foster And Pullen Ltd. This booklet contains examples of their special products e.g. suspension lamps, lanterns and accessories.
General Electric Review by General Electric (USA). Volume 42, No.3 contains a number of articles on various aspects of lighting.
Osram Bulletin by the GEC. A classified index of all lighting articles which have appeared in the Osram Bulletin.
Holophane "Correctalite" Reflectors by Holophane. An illustrated folder.
Selling Light, No. 18 by Philips Lamps, Ltd. Contains articles of topical interest.
P.E.P by the Political And Economic Planning Group. A study of the gas industry and took five years to complete.
Lighting: Publications

Report Of Special Meeting Called To Discuss "A.R.P. And Lighting" p11
The meeting was held with Mr. C. W. Johnson (Under-Secretary of State at the Home Office) where he was questioned about policy.
The President: The objective of the meeting was to obtain information and advice, and to offer advice, with a view to securing some improvement in street lighting, and to discuss various problems which had arisen with regard to it since the war commenced. Once result of the black-out would be to make the public more than ever appreciative of the value of public lighting. The desire was to achieve some improvement in street lighting during war-time - they were tyring to provide lightign which would be invisible to an air raider.
Johnson: The Government was carrying out a certain strategic policy. The situation in regard to public lighting had developed since the outbreak of war in a very different manner form that which was expected. There had been no heavy air raiding. The policy which the Government had started, and was maintaining, was the of achieving as nearly as possible an absolutely black-out. It had taken quite a long time at the outbreak of war to get the black-out well in operation, and if the authorities started "letting up" on any kind of lighting, it would spread, and it would take an appreciable time and a good deal of effort to get back to the present position. Essential services must been maintained. Certain types of lighting were required: for example, for railway marshalling yards, certain essential constructional purposes and so on. The lighting for such purposes was reduced to the intensity which was considered to be safe and was allowed on condition that adequate and watertight arrangements were made to turn it off when an air raid warning was given. As regards street lighting, was it right, was it possible and was it safe to have a system whereby the lights could be extinguished when an air raid warning was given? There were towns where some of the lighting could be turned off, but very few towns where it could be all turned off. (He believed there was only one.)
Johnson: If street lighting was turned off suddenly when an air raid warning was given, and people were looking for shelter, then panic might arise - a worse state of affairs if there had been no lighting at all. Therefore the Government had proceeded on the basis that, if there were to be street lighting, it much be such as could safely be left on. Experiments before the war indicated that an intensiy of 0.002 foot-candles on the ground could be used in places such as railway platforms. (This would give sufficient light for people to find their way, the areas to be illuminated were small, and the platforms were under canopies.) Experiments continued from this point with street lighting, and the Home Office had had the help of the Committee appointed by the Illuminating Engineering Society (which included the APLE). Quite an extenstive experiment had been conducted on the 0.002 foot-candle standard: but due to the bigger areas and lack of canopies, aerial observations showed that 0.002 foot-candles was not safe for street lighting. The experiment was still in hand, delayed by bad weather. An intensity of 0.0005 foot-candles was sufficient to enable people avoiding sandbags, lamp-posts etc. But before a decision could be made, the Home Office must satisfy the other parties concerned in the general policy that it was safe to allow that intensity, and it had not been able to do that yet.
Bailie R. Gemmell (Convener of the Police Committee and Lighting Sub-Committee, Glasgow): A deputation from Glasgow had visited the Home Office and had been received by Mr. Johnson. A plan of the City's lighting was submitted: within the City there were 20,000 lights which could be lit in four seconds and could be extinguished in the same time. Glasgow was of the opinion that there should be a modified system of lighting in the public streets. The Corporation was ready to fit up a main street in Glasgow to prove to the Home Office that something could be done. The biggest part of the population of Glasgow lived in tenements, and the people had almost rebelled to secure the lighting of the stair-heads. Out of 95,000 stair-heads, 63,000 had been lit. There were also some lights under railway bridges. Aslo in industrial areas there were glowing blast furnaces and lights in the shipyards; if the glow from furnaces could be extinguished in seven minutes, and if street lighting could be extinguished in four seconds, why should there not be some street lighting?
Mr. P. Good (British Standards Institution, Joint Committee of IES, APLE and Home Office): The Committee had been invited to make technical recommendations to the Home Office. It accepted the Government's view that, at all events in the present, there should be a black-out as complete as could be achieved. The decision of the Government was taken on the basis of a great deal of knowledge which was not available to most of the concernd with public lighting, and the proper attitude was to endeavour to satisfy the authorities that the lighting engineers could provide something suitable; when the conditions justified a release from existing restrictions, they should accept that release. It was easy to say that street lighting could be switched off when a warning was given but that was a superficial outlook. Street lighting had to be co-related with all the other aspects of lighting, including direction signs etc., and the endeavour had been to provide an effective measure of street lighting properly corelated with all teh other aspects of the problem, and to submit it to aeriel observation and to consideration against the background of knowledge which had been gained. A scheme had been found which might prove satisfactory at an intensity which could be allowed to remain on, and the workers concerned were astonished that it was possible to produce effective street lighting at the levels at which they had been working.
Bailie Horne (Edinburgh): The Government would not move [from their position]. Edinburgh was leading a revolt against the black-out conditions of the present time. He mentioned a cartoon in which Hitler was telling Goering that there was no need to bomb London while there were so many accidents on the streets. 90% of the citizens of Edinburgh would rather run the risk of an air raid than run the risk of death by accident in the streets every evening throughout the year. He said that huge docks, railway sidings and two prisoners-of-war camps were lit up, where as no street lighting was allowed; he pleaded for a modified system of street lighting. There had been casualties through people falling down steps, and as the result of experiments, some of hte steps in Edinburgh had been lit in such a way that the lighting could not be seen from above.
E. E. Hoadley (Maidstone): The present restrictions endangered the safety of the public. One method of tackling the problem was to have a system of street lighting so low an intensity that it could be kept alight during air raids; the second was to allow the street lighting to be extiingushed in 90 seconds as a maximum. As to the suggestion that the sudden extinguishing of lights in the event of an air raid would cause panic, he could not imagine that hte panic would be greater than might occur in an already darkened street. Fighter Command said that the light haze over a town could be seen from a distance of 50 miles in suitable weather. He had had a good deal of experience of that sort of thing during the last war; warnings had been given in London and and street lighting that had been in use had been extinguished.
F. Baker (Yorkshire Electric Power): There was a necessity for some light after an air raid to facilitate the transport of injured persons to hospital; and a number of surveyors had asked what they could do to provide light for repairing broken sewers and other essential services. Sir John Anderson stated that switching arrangements for controlling all the street lighting were not possible: but a number of towns and cities had ripple control or D.C. bias systems.
W. E. Greenhalgh (Bury): Surely the Home Office would recommend lighting which could be switched on in the event of fog, in preference to lighting flares and fires. In the event of fog, if he switched on some lights, he would be breaking the law; but if he lit open fires in the streets he would be within the law. That was ridiculous in the extreme. One department of the Home Office had issued hurricane lamps to fire brigades, on the other hand they were told that there must be no lights at any price. He could light and extinguish the lamps in Bury within seconds. Another suggestion was that the art of camouflage might be extended by providing a little lighting in some remote country districts which could attract raiding aircraft.
Alderman Thraves (Sheffield): Pleaded for some alleviation of the tremendous strain on public service vehicle drivers. He also argued for some form of light at pedestrian crossings. The Home Office appeared discouraging with regards to a modified scheme of lighting. The lights in Sheffield could be extinguished in very few secodns and could be masked to a certain extent. He begged Mr. Johnson to ephasise that there was a very real desire on the part of the people for some alleviation of the present black-out conditions. In Sheffield, the accident rate had doubled.
Mr T. Wilkie (Leicester): He could not accept the inference made by Mr. Good that the Home Office was consistent i.e. one might consider the colelctive effect of thousands of torches as against a fixed light. There had been a half-promise of public lighting of 0.0005 foot-candles intensity. To achieve that intensity, which would hardly allow one to see, a capital expenditure of 20s or 30s would be involved and he felt his Committee would say it was not worth it. The lighting system in Leicester was controlled and sectionalised and if bombing or fires occurred in any section, he could provided light by means of an impulse through the system. He could tell at once, from his board, if lamps were still burning. Whilst an intensity of 0.0005 foot-candles was better than nothing, cities having a control system should be allowed a little more light. Then, in the event of an air raid, the controlled lights could be extinguished, and the low intensity could remain. In his view there was no more risk of panic if lights were switched out than if there were no lighting at all. The switching on of lights after a raid, indicating that the trouble had passed, would have a valuable moral effect.
Mr. Ridley (Birtley, Co. Durham): The present policy was one of funk. There should be more light to reduce accidents and to remove the "curfew." The lights in a village could be extinguished within 1½ or 2 minutes, and the people were very anxious for a modified lighting system. When in London, he had asked the opinion of about 20 Metropolitan policement, and they had all agreed that there should be some form of lighting in the City. (All Chief Constables were against any form of lighting.)
Mr Burrell (St. Helens): He was definitely against any form of quick extinction of lights which he regarded as dangerous. A modified system of lighting, which could be left on, would be much better than sudden extinction, because some light would be required for rescue work after a raid.
Mr. E. C. Lennox (North-Eastern Electric Supply Co.): There was room for a modified form of street lighting. If the black-out had proved anything, it had proved that expenditure on street lighting was well worth while. Road accidents had increased so greatly and had proved the necessity of some street lighting. In his part of the country there were at least ten large araes having controlled lighting. In his view, the morale of the people would be improved if there were a little lighting, which would enabled them to go out at night.
Mr. W. N. C. Clinch (Brighton): The installation in Brighton of loudspeakers for giving public announcements, could also be used as sirens. In fixing the loudspeakers, certain street lighting overhead wiring had been used, and several more wires would have to be provided to give a form of lighting suitable for times other than air raids - but the cost was not great. There must be central control, and the lights should be switcehd off, not necessarily when an air raid warning was given, but probably a little earlier. There had been cases in which lights had been extinguished and there had been no panic.
Mr. D. G. Sandeman (Stepney): In order to provide some lighting during the war, it was not necessary to spend large sums of money on gadgets, but the Home Office would not sanction the expenditure.
Mr. T. A. G. Margary (Wolverhampton): In some experiments on some important pedestrian crossings, he had used very low candle-power concealed light on top of an ordinary Belisha Beacon pole, the light being directed onto the pedestrian crossing. On ordinary nights, a motorist could see a pedestrian on the crossing quite clearly. There were police constables on duty always at these crossings and could switch off the lights by hand in the event of an air raid warning. The Home Office had taken the right course starting from complete black-out and working up to an allowable degree of ligthing. Although an intensity of 0.002 foot-candles was very low, it was the fact that when gas lighting was first replaced in the premier borough of London, the standard of lighting in the ordinary streets was 0.002 between lamps; so the intensity had been a recognised standard.
Mr. Charles Worswick (Oldham): Wanted to know the percentages of daylight and night-time raids respectively.
Mr. Johnson Reply: The Home Office had to carry out the policy which was thought to be in the national interest. One of the points to be borne in mind was that street lighting set up a glow in the sky which was visible over long distances. In the dark, an airman might know his position more or less, but not exactly, and if the lighting in a row were not extinguished quickly, the airman might obtain from it that confirmation of position. With regard to control, the Home office was in process of collecting the information, but believed there were relatively few places in the country having 100% control. (Bailie Gemmell said that 20,000 lamps in Glasgow were controlled; but there were also about 16,000 gas-lamps which were not controlled. So, little over 50% of the lighting in Glasgow was controlled. And stair-heads were internal.) The production of iron and steel must continue. The screening of the glow from furnaces was a long job, but screening measures were being pushed on as fast as possible; but it did not follow that because glare was allowed, street lighting should be allowed thoroughout the country. He imagined that flares would be used near the scenes of bomb damage for repair rather than dim street lighting. The problem of public service vehicle driver was a special one and a modified form of headlamp mask was being tried out to light nearer the vehicle - the lighting of pedestrian crossings was also being considered. As lighting gave a glow in the sky, the question as to whether or not it was safe to allow street lighting did not depend on the existence or otherwise of a control system. The Home Office was in constant touch with the Ministry Of Transport about street lighting, and constant watch was kept on the problem of road accidents, the increase of which was very much deplored. Lighting was allowed in Paris and was centrally controlled. It was difficult to determine how much lighting was allowed there. The rest of France was said to be pretty well as black as the towns in the UK.
Mr. R. Lee (St. Pancras) asked by the APLE was not invited to take part in the deliberations of the Home Office.
Mr. Johnson replied that the Home Office had the benefit of the advice of Committees of the Illuminating Engineering Society on which the APLE was represented.
Mr F. Baker (Yorkshire Electric Power) asked for views with regard to lighting to assist clearing up after air raids.
Mr. Johnson replied that for such purposed localised lights would be better than a general reduced system of street lighting. Also a specification for the lighting of air raid shelters, trenches and their approaches was being issued that day.
Lighting: ARP, Lighting: Control , Lighting: Environment, Lighting: Levels, Lighting: Signs, Lighting: Specifications, Lighting: Users

Calibrated Nipples For ARP Gas Lighting p16
While the requirements of the industry with respect to the new ARP gas lighting are being decided, one manufacturer is ready for any calls that may be made upon them. The manufacturer of gas nipples has been the special care of the Birmingham firm of Amal Limited who have developed a system of calibration, which enables the manufacturer to chose from a wide range of orifice sizes and be assured of their uniformity. Amal Limited make nipples to customers' specifications but have also produced a standardised nipple with 1 B.A. thread.
Lighting: ARP, Lighting: Manufacturers

Shop Window Lighting Box Fitting p16
Deals of a shop window lighting box by Siemens which is shipped in collapsed form and complies with Home Office requirements.
Lighting: ARP

Hebburn p119
Description of the installation in Hebburn.
Lighting: Installations

The Importance Of Planning Lamp Positions in Street Lighting by H. W. Gregory, M.I.E.E. p120
The principle direction in the practice of Street Lighting which had varied since the MOT Report was issued was the departure of lamp positions from a stereotyped pattern as used in BSI Specification No 307 i.e. the "units of system." This led to what appeared to be the irregular planning of lamp positions which came from the necessity to study every lamp position in order to make it most effectively in rendering good visibility. This is because visibility is most efficiently obtaiend by means of a silhouette where the obejct is viewed as a dark patch against a higher background brightness. (This principle had been gaining ground for some years, is voiced in the MOT Report, and remains still unchallenged.)
At the I.C.I. Congress in Holland were the exponents of the opposite school, which is strongly represented on the Continent, where cut-off and semi cut-off fittings at comparatively close spacing are utilised to give high illumination of objects. However, it did not change the mind of those who concluded that the silhouette method gave the greatest visibility at a given cost of installation.
It is hoped this Paper will serve to stress the great importance of considering each lamp individually and guide the designer in weighing the relative importance of the factors involved when a choice of position is possible.
Why the change from high brightness of the object to high background brightness? And why has street lighting practice been so slow in recognising this principle? It is been due largely to the appearance of the electric discharge lamp, which at first provided only high powered sources, at increased capital cost. The higher output suggested higher mounting heights and suggested the possibility of greater spacing to achieve economy. This was my personal view when collaborating with the manufacturers on the first installation of the new lamps along Watford Road in 1933: on the basis of the wider spacing it was practicable to push up the mounting height without unduly increasing the first cost of the installation.
The many workers in the field of background brightness included Mr. Lucas and his film showing the driver's view as he proceeds along the road. Also Mr. C. Dunbar on "Brightness Contrasts", Mr. F. C. Smith on "Revealing Power" and Mr. Waldram on the principle of background brightness. The latter paper examined the "T Patch" and he worked with Mr. Wilson on the effects of coalescing these patches. (Some common misconceptions: the shape of the T patch is under the control of the light distribution of the fitting; a long horizontal light source would broaden the patch of illumination.) The arrangement of the glassware of the fitting can control the brilliancy of the light patch, but cannot control its shape, except to shorten it when cut-off fittings are used.) On the other hand, it can control entirely the brightness of a body by direct illumination, which is the principle used before. The mounting height has an appreciable effect on the width of the light patch and reduces glare. There are only limited possibilites of improving the light patch by mechanical means.
Other early experiments with the Watford lantern, which utilised a stronger beam of light thrown in the direction of moving traffic, proved disappointing, since this defeated the principle of background brightness. The lighting of dual carriageways provides a direct contradiction to the early experiments of trying to copy the beam of a motor car headlight to secure adequate visibility. The new system used on the Great Chertsey Road is such that better visibility is obtained from 125W Mercury Discharge Lamps than from 400W lamps in older equipment: this also provides a rough measure of the comparative efficiency of obtaining visibility by the two methods of object brightness and background brightness. Also when obtaining visibility by object brightness in accordance with the older conception there were always long stetches of mid-span position where background brightness had to be relied upon: consequently a driver was continually required to change his method of vision from one principle to the other. Consequently a driver was continually required to change his method of vision from one principle to the other and by utilising only the conception of background brightness, much fatigue and strain on the driver's senses is obviated and greater driving comfort is secured. For this reason along, I think it was worth the wholesale adption of the newer principle.
The composition and colour of the road surface is far less important than one might at first suppose. At the high angles of reflection utilised, it is the degree of polish of the surface by tyres which matters in securing the spread reflection of the light source. Fortunately all types of road surface wear down to a comparatively common polish. The coarser grain of the surface associated with a non-slipping tendency provides the better diffusion which broadens the light patch. The streak of the light patch associated with a surface flooded by rain has removed the coarseness by filling the interstices with water. As one approaches a lighting source the efficiency of reflection in the road surface at reducing angles of vision is rapidly reduced such that near the lamp we are not troubled with excessive brightness and glare from the light patch.
There is also the importance of utilising the illumination of vertical surfaces such as hoardings to provide a bright background.
The motorist's requirements for public lighting are the most exacting if if we cover his requirements, then the requiremetns of other bodies of users, even the private householder who likes some stray light to deter burglars, are met. The driver does like to know something of what is bordering the thoroughfare.
The principles involved in the siting of lamps for special positions (such as roundabouts, bends and junctions) are: (1) To draw the attention of drivers at a distance to the presence of the turning, roundabout etc. (2) To reveal the presence of traffic in the turning or roundabout and its approaches and to make clear the confines of the carriageway. These purpose are met in all cases by providing the necessary road brightness.
A very common plan for designing installations during the past 30 years has been to start with trial positions of lamps in the street under review opposite the ends of road junctions. This mets the dual purpose of lighting the thoroughfare and providing a "mid-horizon" lamp for the use of traffic in the side road approaching the main thoroughfare. Thre requirements of the new specification are still in line with making the first trial plan along these lines and fitting the remaining lamps in accordance with the principles in the specifcation.
The new Specification simplifies the planning of street lighting by resolving the eight former classes into the two classes A and B of the MOT Report, which specifies the power, mounting height and the spacing in such a way that one only has to specify the precise positions for the lamps. The main objective is to be obtained by adequate background brightness.
I have reached the same conclusion as the MOT Report, namely that the planning of lighting does require experience in the designer and demands that Lighting Authorities should be advised by an Engineer. Much of the forthcoming Specification will reduce public lighting design to a common factor, the actual success of any particular installation will in finality rest of the wise and exact siting of each individual lamp.
In summary:
(1) Primary object in planning lamp positions should be to ensure road brightness, so approaching observer can perceive objects by silhouette.
(2) The typical observer should represent a car driver, whose requirements are the most stringent of any user of the road. Meeting these requirements will generally satisfy those of other users.
(3) Sufficient light sources must be employed to ensure reasonably covering the road with light patches and to ensure they coalesce.
(4) Regular spacing of light sources (except on straight and level road) will be the exception rather than the rule.
(5) A simple plan of the installation which gives no idea of the perspective view of the driver is quite insufficient on which to judge the merits of a design.
(6) It is necessary to view the road itself, with its boundaries and confines and changing elevations when finally planning any installation.
(7) Valleys in teh road may not require special treatment but hill-crests may require closer spacing with cut-off fittings.
Lighting: Installations, Lighting: Specifications, Lighting: Theory

For Your Information p19
With recent movements in Street Lighting and the introduction of Specifications etc., quite a number of people effected will be in need of detailed and amplified information. It is a feature of the Government Orders dealing with Street Lighting in war-time that both supplier and consumer are pinned down strictly to adhere to very fine technical details and in view of the heavy responsibility under which both work, many engineers feel it desirabel to have additional information, and advice in many cases. The Journal will set up an Information Department for the purpose; this column will therefore be a feature for receiving and giving answers to such enquiries.
APLE: Journal, Lighting: ARP

Peace-time Lighting p20
Picture of installation in Memorial Square, Coalville.
Lighting: Installations

Discomfort Glare In Lighted Streets by R. G. Hopkinson, B.Sc.(Eng.), F.R.P.S. p21
Extracts and summary of his paper which was given to the IES in London on the 9th January 1940
"Discomfort glare was found to be influenced by the general brightness of the scene, by the angle between the direction of a glare source with the line of sight, and under street lighting conditions, by both the intensity and intrinsic brightness of the source. The glaring effects of a number of sources were found to be additive. No difference on the glaring effects of yellowish, bluish and white light could be detected. It had been found possible to express the results in a form easily applicable to problems of street lighting design."
The paper distinguishes between discomfort glare and disability glare. "There is the effect which glaring light sources have on the comfort of the observer. Glaring sources which amy have but a small effect on the ability to see may yet cause very considerable distraction and discomfort. This is Discomfort Glare.

Principles Of Measurement
There are four degrees of discomfort glare:
(1) Just Intolerable: The change-over point between intolerable and uncomfortable.
(2) Just Uncomfortable: The point where glare is definitely distracting but only just uncomfortable. The term "uncomfortable" is associated with some observers with the desire to shade the eyes. The term "distracting" implies the sources of sufficiently noticeabel to attract the observer's attention.
(3) Satisfactory: The point where sources, still noticeable, are deemed sufficiently unobttrusive to cause no distraction.
<4) Just Not Perceptible: The point where the glare of sources is no longer noticable. The sources are still visible but merge into the general field of view.
Main Conclusions
"If the surround (road) brightness with which each of a number of single sources gives a certain degree of glare is measured in each case, the arithmetical sum of these brightnesses agrees closely with the the measured value of surround (road) brightness chosen to give the same degree of glare when all the sources are presented together. This is a result of practical value. It means that the conditions necessary to establish a given degree of glare in a complete installation can be estimated provided the conditions necessary for the same degree of glare are known for the individual sources."
"The general brightness level of an installation is an important factor in determining the magnitude of the glare from the installation." In an installation judged "just uncomfortable", a reduction in the general average brightness level to one-fourth, would increase the glare such that it is "just intolerable." If the general brightnesss level had been increased four times, the glare would be decreased such that it would now be considered "satisfactory." A further increase of four times in the general average brightness level would decrease the glare to just "perfect."

Means Of Reducing Discomfort Glare
"There are several methods by which glare can be reduced, applying the principles deduced from the investigation." Discomfort glare is only one of the many variables which combine to determine the excellence of an installation.
(1) Increase The Flashed Area Of The Sources: An increase in the flashed area of the sources will bring about a reduction of discomfort glare. This method is of value because it does not affect the revealing power, the disability glare or brightness of the installtion, so long as the light distribution from the lanterns is unaffected. If any appreciable reduction in discomfort is to be obtained, the flashed area of the lantern must be at least doubled.
(2) Increase The Mounting Height: The discomfort glare from an installation of sources mounted at 15' would be very likely be reduced if the sources were mounted at 25', provided the road surface had a good degree of polish.
(3) Reduction Of Spacing Of Lanterns: A more closely-spaced installation of sources of lower intrinsic brightness will probably be less glaring than a longer spaced installation of high intrinsic brightness.
(4) General Reduction of Source Intensities By Reduction of Source Intrinsic Brightness. A general reduction of the intensities of all the sources of an installation e.g. lower-powered lamps, will reduce somewhat the degree of discomfort glare obtaining, but the method should not be employed unless it is certain that the reduction in discomfort glare more than outweighs the loss of revealing power.
(5) Change of Light Distribution From Lanterns: The less the intensity produced by a lantern in the direction of the eye of the observer, the less discomfort it will produce for a given road brightness. Therefore, if the intensities of the galre sources are reduced, at teh same time retaining constant the same background brightness, the discomfort glare will be reduced. This ideal is obtained by the complete cut-off type of installation, provided that the spacing is sufficiently close and the available light flux sufficient to give a high road brightness. Economic factors prevent an easy solution to the glare problem - it is just those directions which cause glare to the observer that the light sources of an installation have to emit fairly high intensities if uniform brightenss and adequate revealing power are to be attained with reasonable spacing and cost. Discomfort glare is to a large extent complementary to the economical provision of high road brightness, high revealing power and otherwise good apperance.
Lighting: Distribution. Lighting: Theory

London Laughs p22
Cartoon from the Evening News.
Lighting: Social Comment

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