mailing list
site map

ilp archive : journals

public lighting no. 31 vol. 8
October-December 1943 Conference Number (2)

Editorial p65
Good News p65
Lighting of roads after the war continues to make "front page" news in the Daily Press. The main signs of the possible return to normal street lighting is looked forward to with keen anticipation. However, the press read too much into the APLE's leaflet ("Prepare Now To Light Up Your Street") which caused some embarrassment in certain Government departments.
No official instructions have been issued by any department granting a departure form existing Lighting Restrictions Order.
Each day brings street lighting as we knew it in 1939 nearer. When that day of liberation from restrictions shall come, will a large number of lighting authorities be in a state of unpreparedness. The years of war have taken a toll on the equipment that has stood idle in all weathers - some will want renewing, all with need overhauling. Prepare now, don't delay!
Lighting: ARP, Lighting: Maintenance

Street Lighting As Road Safety p65
Sir Charles Bressey wrote a piece for the Daily Sketch which was given prominence. "Even when the black-out is finally abolished, road-users will still be imperilled by erratic lighting. Every motorist knows how his sight is strained and his nerves racked by the sudden transitions from a dazzingly illuminated shopping-centre to a pitch-dark road beyond the borough boundary where a rural district council holds sway. One remedy for the indefensible irregularity of street lighting would be a drastic reduction in the number of lighting authorities and the concentration of powers under a few well-equipped public bodies. It is said in the Tyneside aread there are 13 different authorities responsible for illuminating a 20-mile stretch of roadway."
Lighting: Authority Organisation, Lighting: Safety

The Design Of Lamp Columns And Fittings In Relation To Post-War Town Planning And Reconstruction by H. C. Bradshaw, C.B.E., M.Arch., F.R.I.B.A., Secretary, Royal Fine Arts Commission p66
Summary of the paper.
Lighting: Design

Street Lighting Lantern Design In Relation To Town Planning by S. English D.Sc., F.I.C., F.Inst.P (Technical Director Holophane Limited) p67
Summary of the paper.
Lighting: Design

Good Lighting Means Greater Efficiency p72
Details of increasing production at a factory producing war material by installing Sieray Fluorescent Tubes by Siemens Electric Lamps And Supplies Limited. Average lighting in the Erecting Shop was 8-9 foot candles, whilst those over benches and machines were 20-30 foot candles; whilst in the Drawing Office, trough reflectors mounted diagonally to the drawing board, provided 15-16 foot candles. There is an umlimited future for fluorescent lighting for indoor illumination.
Lighting: Lamps

Street Lighting Contracts In War-Time p72
On the 15th December, the House Of Lords' Law Lords found in favour of the Egham Urban District Council against the Egham and Staines Electricity Company Limited. Under the street lighting contract, the Electricity Company claimed £3950. The contention of the defendants was, that owing to war-time restrictions and black-out regulations, the streets had been unlit. Mr. Justice Cassels, in the lower Court, help that the Urban District Council should pay to the Electricity Undertaking. That decision was reversed by the Court Of Appeal on June 17th 1942. The Electricity Company thereupon appealed to the Lords and this was dismissed with costs. Lord Russell of Killowen said it was contended by the Company that the current had been supplied up to the point of entry into the lamps and no default had occurred. He could not accept that contention. The constract was not to supply merely electric energy, but to supply electric lightng. There was complete exoneration of the Council.
Lighting: Legal

New Members Elected To The A.P.L.E. p72
List of new members.
APLE: Organisation

Post-War Street Lighting By Gas by W. J. G. Davey and W. Hodkinson p73
Paper presented at Gas Industries House on Thursday, 23rd September 1943
When hostilities cease: there will be an immediate demand for street lighting; damaged columns and lanterns will require replacement; complete new installations will be necessary; and a hundred accessorties will be required in quantity. Manufacturers of street lighting equipment are engaged on whole-time war work and the change over to peace time products will take time. Raw materials will not be immediately available and are likely to be issued on licence. However, a great deal can be done by prior planning.

How can a lighting installation be assessed?
There are two documents which give guidance. The first is British Standard Specification 307, 1931 (out of print, but not yet replaced) and the second is the Final Report of the Departmental Committee on Street Lighting set up by the MOT and published August 1937. To assess the lighting installation the following factors should be considered:
Classification Of Streets
In BSS 307:1931 there are eight classes A-H. These depend upon the minimum horizontal illumination at a special position on the road surface relative to the light sources called the test point. The Final Report allows for two classes of roads only called Group A ("All those roads in built-up areas which are included in the MOT's system of classification may eventually have to be regarded as traffic routes, together with other roads considered to be principal arteries") and Group B ("Other roads, which the authority considers shuold be lighted").

Mounting Heights Of Light Source
"There are two opposing factors in operation as the height of the lamp is increased. The vertical angle from the light source to a point on the ground is decreasing, tending to increase the horizontal illumination at the point. While the actual distance from the light source to the point is increasing, decreasing the illumination. The limiting mounting height to give maximum illumination may be determined from the forumla H=D/sqrt(2) where H is the mounting height of the lamp and D the distance from the point from the lamp base. Moreover the effect of raising the mounting height from 10' to 17'6" (+65% illumination) is greater than increasing the mounting height from 17'6" to 25' (+32% illumination). There are those who consider the mounting height of 25' in the Interim Report (good Class F illumination) to be excessive and 20' is reasonable. One might suggest that if the increased cost of installing and maintaining the 25' column against the 20' column is not compensated by the increase in horizontal illumination (less than 32%) there may be something to be said for 20'. Increased mounting height is always followed by reduction in average illumination but also a reduction in glare." Any increase in mounting heights should be considered in relation to lamp spacings: the shorter the spacing, the lower the mounting height etc., whilst the vertical angle between the midspan point and the light source should be kept above 55°.

In BSS 307, spacing-height ratios are given for the various classes of streets. These are in general agreement with the Final Report.

Arrangement Of Lanterns
BSS 307 allowed for staggered, opposite, central, single-side and opposite/central, the Final Report favoured staggered (with single-side on bends) and central (for tree-lined roads).

Overhang And Width Of Roads
The Final Report recommends:
(1) For roads up to 30 in width: No overhang, lamps mounted vertically over kerbs. For very narrow roads, the lamps may be mounted behind the kerb line, provided the distance between rows does not exceed 30'.
(2) For roads from 30 to 40 feet in width: Lanterns should be suspended over the roadway, overhang being equal to half the difference between the actual width and 30' i.e. distance between rows of lamps is 30'.
(3) For roads exceeding 40 feet in width: lanterns should be mounted over the kerb, with additional lanterns mounted centrally at intervals not greater than three spans in length. When this impractical, lanterns should be overhung 6 feet into the roadway, but for roads greater than 50', no installation is satisfactory without central lanterns.
(4) Dual carriageways having centre verge not wider than 6': Lanterns mounted over the centre verge to form staggered system for each carriageway with lamps mounted over the outer kerbs.
(5) Dual carriageways having centre verge wider than 6': A double row of lanterns should be mounted over the verge to form a staggered system with the lamps mounted over the outer kerbs. Overhang of lamps will depend on the widths of the carriageways. With very wide centre verge, two rows may be necessary.

Siting Or Positioning Of Lanterns
The Final Report makes several recommendations for T-junctions, cross roads, roundabouts and bends. Examples are given of several gas-lit roads, mostly in London, detailing how they can be improved to conform with the Final Report from the Interim Report or BSS 307.

Directional Equipment
To make the most of the lighting installation, a great deal of thought and care are necessary in the preliminary planning and siting of lamps. The lighting engineer will be greatly assisted by fittings whose directive equipment can be adjusted both vertically and laterally. The latter is most important as straight roads are normally the exception. Directive equipment will help but first importance must be attached to the positioning of the lamp columns.

The Quantity Of Light Or Degree Of Illumination
BSS 307 classified streets according to the horizontal illumination at the test points. The Interim Report suggested that effective illumination was one associated with a generously planned Class F. The lighting units should be of at least the numebr and power of those required for this standard i.e. about 0.07 foot-candles. In the Final Report, illumination is replaced by the power of lanterns: the amount of light to be provided per 100 feet linear of road, having a carriageway of not more than 40 feet in width should exceed 3000 lumens and be less than 8000 lumens. These figures refer to the luminous output of the lantern.
A generously planned Class F is obtainable with gas lighting for an expenditure of much less than 3000 lumens per 100 linear feat. [The paper questions why such a high lumen output of 3000 lumens is required for Class F] In one example, a test point illumination of 0.06 foot candles is provided for an expenditure of 1860 lumens per 100 linear feet. Other examples were given in [1].
The purpose of street ligthing is not to use as many lumens as possible. According to the Street Lighting Committee of the American Illuminating Engineering Society the purposes of public lighting are:
(1) To promote safety and convenience in the streets at night through adequate visbility
(2) To enhance the community value of the streets.
(3) To accomplish the illumination of the streets with the greatest practical promotion of the aesthic qualities of the street and the street lighting equipment.
Above all, it is not lumen output but visibility that is required. If satisfactory illumination can be obtained by the use of fewer than 3000 lumens per 100 feet linear, it is more economical to use the smaller number of lumens, and with gas lighting a minimum of 2000 lumens per 100 linear feet is not too low a minimum.

Distribution Of The Light
In the author's opinion, the lumen criterion has no justfication whatever. It is the amount of light falling upon the carriageway and the scientific distribution of that light which governs good visibility, and the quality rather than the quantity of illumination, is the only feasible basis upon which a street lighting installation can be assessed. This is admitted in the Final Report.
We can now consider the question which prefaced this paper: "How can the pre-war lighting installation be assessed? Can a particular installation be brought up to date? Should the installation be replaced by a more modern one?"
The guide will be the Final Report.
In what group can the street be placed? Is it a traffic route? If so, are mountings and spacings in accordance with Group A requirements? If not, a new installation must be considered. In the cases of other roads, modified spacings should be adopted to fulfil the recommendations and extension pieces fitted to the lamp columns to bring them up to the 13-15 feet mounting height. In both cases, the siting of lamps is of paramount importance, taking into account bends, T-junctions, cross roads and roundabouts.
With regard to the type of lamp, all firms are concerned with the war effort. On the cessation of hostilities the 1939 gas street lamps will be the latest and most up-to-date for some time, until research staff and operatives can leave their present jobs and settle down to their peace time avocations.
The Final Report forms a splended basis for a Code of Good Street Lighting Practice. If its recommendations had been acceptable then the Final Report would've been supplemented by a British Standard Specification before the war. The recommendations are good on the arrangements of lanterns, overhang and the siting of lamps.
If the distribution of light from lamps decides the characteristics of the bright areas, then such characteristics are equally bound up with the illumination distribution. This can be measured - and can be used to ensure satisfactory maintenance. Illumination points should be used to determine performance - not total output of the lantern as stated by the Final Report

The Assessment Of A Lighting Installation
The judgement of an installation by the horizontal illumination at one point relative to the light source (whether mid-point or test point) resulted in light being thrown in particularly direciton to other parts of the carriageway. This, as used by BSS 307, proved unsatisfactory and unreliable. This could've been avoided by having several test points.

The Tools Of The Lighting Engineer
Lumen Output
This can be determined directly by integrating spheres or cubes, or may be calculated from the candle power distribution. Or, for symmetrical distributions, take the mean of the candle powers at the "Russell angles" (which will approximate the mean spherical candle power) and multiply by 4*pi to get the total lumen output. For asymmetric fittings, the candle power varies in the horizontal as well as the vertical plane, and instead of Russell angles, it has proved of advantage to make a plan of the candle power distribution of some form of equi-areal projection of a sphere, and to determine the mean spherical candle power from this. The Sandon-Flamstead sinusoidal projection possesses the advantages of ease of construction and ease of interpolation and has been adopted - it was used in BS 307 hwere it was used for the determination of average illumination.
The introduction of the Sandon-Flamstead sinusoidal projection was met with some criticism and some amusement as it resembled an onion. In the immediate pre-war days it was accepted by the majority of lighting engineers. It is an equi-areal projection so areas can be compared. The angular position of any point of the street, with reference to the light source, can be found from this diagram. The sinusoidal diagram of light distribution is the most useful tool in the hands of the street lighting engineer, and it is essential they should have complete understanding of it.
The sinusoidal diagram of the Maxill G 12-light No. 2 mantles is given. The method of determining the lumen output from the lamp is to use a planimeter and compute the area between the various candle power contours. These are multiplied by the mean candle power between contours and the sum of the products is multiplied by 4*pi/A where a is the area of the diagram. Or place a grid over the sinusoidal diagram of 204 intersections, note the candle power at each intersection, add together and divide by 204 to get the mean spherical candle power, then multiply by 4*pi.

Horizontal Illumination
It is neccesry to determine the horizontal and vertical angles at that point with respect to the light source. The candle power at that point may be read off the sinusoidal diagram and the horizontal illumination calculated. Two nomograms are given for the calculation of angles and horizontal illumination using trigonometry.

The Distribution Of Ilumination
The standard method: the iso-foot candle diagram of distribution of horizontal illumination is prepared by first calculating the horizontal illumination for the given mounting height and various vertical angles, for a series of horizontal angles. The results are plotted against distances corresponding to the vertical angles and from a series of graphs, distances are found at which the illumination equals a definite number of foot-candles. A plan of the street is drawn with radial lines representing the horizontal angles, 0° being a line parallel with the kerb and passing through a point directly beneath the light source. The lines radiate from this point. The distances corresponding to each foot-candle are marked on the respective radial lines and smooth curves drawn. A series of such curves forms the iso-foot candle diagram of distribution of horizontal illumination. This is a tedious process.
A Davey tangential grid is an extended plan of the street. The 0° horizontal line represents the line joining points immediately beneath the lamps on one side of the road. Horizontal angles are radial lines emanating from a position immediately beneath the lamp and positioned on the extreme left-hand side of the chart. The chart is divided into squares of 10 feet sides so the area of the diagram is 150 feet by 125 feet - this is designed for a mounting height of 125 feet. Vertical angles are represented by semi-circles - the scale of these differ depending on the mounting height so for a mounting height of 25', the 45° vertical angle passes through the 0° horizontal at 25 feet. The radii of other arcs are proportional to the tangents of the angles they represent. The tangent of 76° is 4.01 and this multipled by 25' is 100.27 - and the 76° arc cuts the 0° horizontal at this value. The chart is used as follows: the candle power distribution from the sinusoidal diagram is drawn on tracing paper over the chart e.g. the 1000 candle power angular positions are determined and these are plotted and drawn by a smooth curve. The same procedure is adopted for other candle powers. The next step consists of determining positions on the plan representing equal values of illumination. The illumination varies as the candle power and the cubed cosine of the vertical angle for any giving mounting height. For example, with a mounting height of 25', the candle power required for one foot-candle varies from 625 at 0°, 690 at 15° 960 at 30° 1770 at 45° etc. If these and several points are joined by a smooth curve, then one foot-candle contour or the iso-foot-candle line of one foot-candle will result. These is repeated for other values and the kerb lines are then inserted. This can be used to complete illumination distribution due to two lamps. A sheet of tracing paper is again superimposed on the two tracings and points representign the joint effect of both lamps are marked for equal value of illumination, smotth curves being drawn between them.

Average Illumination
BSS for Street Lighting 307, 1931, called for average illumination for any tender, and a method was described for the determination of this quantity, making use of the iso-candle chart on the sinusoidal projection. The area of any part of the sinusoidal diagram is proportional to the corresponding part of the surface of the sphere. The luminous flux in any zone my be determined by the product of the area of the zone, the average intensity over the zone, and a constant 2*pi/A where A is the area of the complete diagram. (2*PI as it's only half the area of the sphere).
In BSS 307, the kerb lines are plotted on the iso-candle chart, and the areas between the various candle power contours within the kerb lines are determined by a planimeter. The areas between contours are multiplied by the value of the upper contour and then the value of the lower contour, and the mean of the sum of the two sets of products is used - this mean value is the average intensity of the lighting unit over the area bounded by the kerb lines, and this multiplied by 2*PI/A gives the total flux falling upon the carriageway from one side of the unit. The total flux is two times this value, for both sides of the lantern. The average illumination is the total flux divided by the area of the carriageway between successive lamps in case of staggered, central and single-side systems. In case of double side system, it's twice the value, and for double-side central then it's three times.
The kerb line, or b/h line, where b is the perpendicular distance of the kerb from the line of lamps and h is the mouting height of the lighting units, may be determined from b/h = tan(a1)sin(a2) where a1 is the vetical and a2 the horizontal angle.
The rest of the paper was slides of pre-war gas lighting untis and installations.
Lighting: Distribution, Lighting: Levels, Lighting: Luminaires and Lighting: Specifications

[1]: The Planning of Gas Installations to Conform with the British Standard Specification for Street Lighting by F. C. Smith, APLE Conference 1932

1944? p87
Pictures of pre-war night-time lighting installations.
Lighting: Installations

Adverts: Poles Ltd, The Association Of Metal Sprayers, British, Foreign And Colonial Automatic Light Controlling Co., Ltd., Siemens Electric Lamps And Supplies Ltd., Metropolitan Vickers Electrical Co. Ltd, Engineering And Lighting Equipment Co. Ltd., Automatic Telephone And Electrical Co., Ltd., British Commercial Gas Association, W Parkinson And Co., Philips Lamps Ltd., The British Thomson-Houston Co. Ltd., Hobbs. Offen And Co. Ltd., William Sugg And Co., Ltd., Holophane Ltd., Walter Slingsby and Co., Ltd., The Horstmann Gear Co., Ltd., British Electrical Development Association, Inc, Foster And Pullen Ltd., Sangamo Weston Ltd. and The General Electric Co., Ltd.