E. C. Lennox, A.M.I.E.E.

Read before: Public Works, Roads and Transport Congress, 1935
Published in: Public Lighting, Vol. 1, No. 1. March 1936; Presidential Address, APLE, 1936.

Keywords: Lighting: Authority Organisation, Lighting: Installations, Statistics: Accident Data and Statistics: Road Data.

1935

Conclusion:
1. The proportion of accidents by night is unduly high.
2. They have risen progressively during recent years due to the increase in the use of roads during dark hours.
3. The increase in accident rate at night is due to lack of visibility.
4. The pedestrian suffers more heavily than the driver as a result of lack of adequate visibility.
5. Good visibility obviating use of headlights could be achieved by provision of efficient public lighting.
6. Crime at night would be materially reduced by providing efficient public lighting.
7. The cost of efficient public lighting would probably be less than the saving it would effect on reduction of accidents and crime.
8. Public lighting is for the benefit of the community as a whole, and its cost should not be borne parochially.
9. No hope of efficient schemes of uniform lighting can be entertained unless public lighting is handled by a Central Authority as in the administration of Roads, Transport, Education, etc.
10. No smaller unit than a County Borough should be a Lighting Authority. In Rural and Urban Areas the County Councils should be the administrative Authority.
11. As in the construction and maintenance of all Public Properties, Street Lighting Installations should be under the control of competent Public Lighting Engineers with a Central Authority, e.g., the Ministry of Transport, to classify roads for lighting purposes, and to set up standards of lighting for various classes of roads (bearing in mind traffic density) with a view to obtaining uniformity.
12. Public lighting is necessary during 46 per cent. of the year, and is more vital to-day than ever before.

References:
[1] National Safety First Association, Survey July-December, 1932
[2] MOT's Report Of Fatal Road Accidents, 1933
[3] Home Office Road Statistics (Fatal and Non-Fatal Accidents), 1934
[4] Victoria Embankment Road Accident Data, 1928
[5] Victoria Embankment Road Accident Data, 1930
[6] Public Safety As Affected By Street Lighting, R. E. Simpson, National Bureau Of Casualty And Surety Underwriters Of America

G. H. Wilson, B.Sc.(Eng.), E. L. Damant, Commander R.N.(Retd.) and J. M. Waldram, B.Sc.(Eng.)
(Communication from the Staff of the Research Laboratories of the General Electric Co., Ltd., Wembley, England)

Published in: The Journal Of The Institution Of Electrical Engineers, Vol. 79, Nos. 477, 478. September, October 1936.

Keywords: Lighting: Lamps, Lighting: Distribution, Lighting: Control, Lighting: Luminaires and Lighting: Theory.

July 19th, 1936

Note: This paper refers to the MA type lamp. It was reclassified as the "medium-pressure" mercury-vapour lamp, after the development of a higher-pressure mercury-vapour lamp, the MB, later the same year.

Abstract: This paper records the experience which has now been gained over three years in the use of high-pressure mercury vapour lamps in public lighting. The engineering and photometric characteristics of the lamps and the design of the auxiliary apparatus are discussed. The overall characteristics of the lamp and its auxiliaries are given, together with certain peculiarities of street-lighting circuits which affect its performance. The effect of the illuminating engineering aspects upon the realization of the efficiency of the lamp is discussed, and the developments of the theory of street lighting which its use has brought about are indicated. Novel designs of lanterns, which are rendered necessary by the peculiar shape of the source, are described; and special optical, thermal, and constructional problems which arise from the use of the lamps, and also other points which have occurred in practical experience, are recorded.

Luminaires: GEC Watford (Z8001), ??? ???, ELECO Arterial, GEC Lewisham (Z8003), BTH Diron, GEC ???, BTH Mercra H.

References:
[1] Paper, J. W. Ryde, G.E.C. Journal, 1933, Vol. 4, p. 199.
[2] Paper, J. W. Ryde, Journal Of The Royal Society Of Arts, 1933, Vol.82, p. 623.
[3] Inaugural Address, C. C. Paterson, Journal I.E.E., 1931, Vol. 69, p. 1.
[4] Electric Discharge Lamps and their Application to Public Lighting, G. H. Wilson B.Sc. (Eng.), A.M.I.E.E., A.P.L.E. 1933
[5] Paper, K. M. Reid and H. J.Chanon, General Electric Review, 1935, Vol. 38, p. 580
[6] Paper, J. W. Ryde, Journal Of The Royal Society Of Arts, 1933, Vol.82, p. 624.
[7] Paper, M. G. Bennett, Illuminating Engineer (London), 1933, Vol. 26, p. 75.
[8] Paper, W. S. Stiles, Illuminating Engineer (London), 1935, Vol. 28, p. 125.
[9] Book, L. B. W. Jolley, J. M. Waldram and G. H. Wilson, Theory And Design Of Illuminating Equipment, 1930, p. 553.
[10] Paper, S. English, Illuminating Engineer (London), 1934, Vol. 27, p. 532.
[11] Paper, S. S. Beggs and G. H. Wilson, G.E.C. Journal, 1935, Vol. 6, p. 127.
[12] Paper, G. H. Wilson, Illuminating Engineer (London), 1933, Vol. 26, p. 151.
[13] Paper, J. M. Waldram, Illuminating Engineer (London), 1934, Vol. 27, p. 305.
[14] The Visibility of Objects in Artificially Lighted Streets, J. M. Waldram, A.P.L.E. 1928
[15] Paper, W. S. Stiles, Illuminating Engineer (London), 1929, Vol. 22, p. 304.
[16] Paper, C. C. Paterson, Journal I.E.E., 1936, Vol. 78, p. 171.
[17] Horizontal Discharge Lamps, R. Maxted, Electrical Review, 1936, Vol. 118, p. 309.
[18] The Importance Of Kinematical Factors Of Roadway Illumination, L. J. Davis, M.A., B.Sc.; R. Maxted, B.E. (Elect.), B.E. (Mech.); G. S. Lucas, M.I.E.E., A.P.L.E., 1935
[19] Paper, H. Rissik, Journal I.E.E., 1933, Vol. 72, p. 435.

L. J. Davis and G. S. Lucas, M.I.E.E.

Read before: Engineering and Technical Societies, Institution Of Civil Engineers, 1938
Published in: Public Lighting, Vol. 3, No. 9. March 1938

Keywords: Lighting: Colour, Lighting: Distribution, Lighting: Levels, Lighting: Specifications and Lighting: Theory.

1st March 1938

Fundamental Principles Of Road Lighting
On a roadway the intensity is less than 1 foot candle. The user of the light may be travelling at high speed and it is essential if accidents are to be avoided that they be able to distinguish the course of the road and possible obsturctions 100 to 200 yards ahead.

Where light intensity is low and the viewpoint is distant from the observer, it is no longer possible to discriminate by colour differences and only brightness contrasts are available.

On a well-planned installation, objects at a distance are seen in silhouette against the bright background of the road. In road lighting, the important factor is not so much the quantity of light reaching the road surface as the amount and direction of the light leaving the surface.

While for most lighting problems, it is sufficient to specify the light reaching the object, in road lighting, owing to the perculiar viewpoint, the high incident angles of the light at the road surface, and the rapid change in teh reflectivity of the road surface at this angles, the quantity of light reaching the road is in itself no criterion of the effectiveness of the lighting.

The test point reading (as used for the existing British Standard) is only of real use as an indication of the deterioration of an installation with time - only of value to the Maintenance Engineer. Two installations having the same test point readings and both satisfying the exiting B.S. Specification may be widely different in their results, one giving good visibiltiy and the other a patchy result.

It has been suggested that a specification might be based on some measurement of brightness distribution of the road surface. However this would be unsatisfactory because:

• A brightness distribution is dependent on the lighting equipment, the arrangement of this equipment, but also on the conditions of the surfaces to be lighted, which vary from time to time. Resurfacing the road, wet and dry conditions, the material and colour of other backgrounds all influence the brightness distribution.
• Owing to the changing field of vision as the observer moves along the road, the determination of optimium brightness is a very difficult undertaking.
• It would be misleading to consider only the background brightness without considering the nuetralising effect of glare.

Therefore although it becomes apparent that the brightness distribution is the criterion of street lighting, it is at present impracticable to use brightness measurements as a basic for a specification.

Faced with this problem, the Ministry Of Transport Committee recommended certain arrangements of lighting units and the quantities of light from the sources which have given satisfactory results under all reasonable conditions found in practice. The Committee has left as much freedom of action as possible to the lighting engineer to permit scope withing the terms of the recommendations for further improvements.

THe Production Of Bright Backgrounds On The Road Surface: The Lighting Engineer's Task

The lighting engineer's task, namely to illuminate roads for safe and convenient night travel, is briefly to provide the motorist with a "bright" background.

The fundamental surface that has to be rendered bright is the road itself. The perculiar viewpoint of the road surface to an observer standing on the surface, and the high angles of incidence of the light from the lanterns, present an unusual problem in lighting as far as the horizontal background is concerned. An observer on the road surface views the surface 100-200 yards ahead at very acute angles and the light from the lantern produced bright areas very different from those seen at more normal angles.

The light patch is T shaped. The position of the light patch is determined by the relative positions of the lamp, surface and observer, and as the latter moves, so the light patch moves.

The size and shape of the bright area is determined by the conditions of the road surface, height of the light source, brightness of the source etc., but by far the greatest factor is the road surface. The highly reflecting surface of a wet road produces bright areas very long and narrow and of high brightness, while matt surfaces produce broad areas of ususally lower maximum brightness. The tendency for the road to become "polished" in use and when wet is an important consideration.

The bright area starts from point under the lantern on matt roads, and on wet and polished surfaces from some point in front of the lantern. Very little light leaving the lantern in a direction away from the observer comes back to him and road surface, and hence the road beyond the lantern appears dark.

The lighting engineer's job is to "patch the road surface" with the T areas of light so that for every normal position of an observer the road appears covered with light patches. On a bend the lanterns are placed on the outer radius so that the light patches fall on the road surface and not on the verge as would be the case if the lanterns were placed on the inner radius. At cross-roads or junctions the lanterns are placed overhanging the traffic lane beyond the road junction, so that the patch of light falls across the road entry.

The light distribution of a lantern much be such that light is thrown at least to the base of the next lantern in the same traffic lane and so the light distribution is closely related to the lantern spacing. With a staggered arrangement of lanterns, and a spacing of 150', the distribution must be such that light is thrown at least 300' along the road in either direction i.e. the light is radiated at 86° Some "cut off" lanterns limit the distribution to 70° and these should be spaced at 90'-100'.

The angles of distribution between 70° and 90° are very important to the lighting engineer. By increasing the angle to 86°, the length of the bright areas on the road is increased approximately four times, but this advantage is offset by the increased light reaching the observer direct from the light souce and causing glare. Criticism was sometimes levelled against widely spaced units of early designs on this account. In more recent lanterns great care is taken with the light distribution at the critical angles to ensure the optimum conditions of visibility and the minimum glare - these are "controlled cut-off" lanterns - the distribution between 70° and 90° is carefully controlled.

It would appear that "cut-off" fittings closely spaced would eliminate glare from all lanterns ahead of the observer and thus result in optimum visibility. This is true for a stationary observer. But as the observer moves along the road, each successive lantern produces glare at some angle, which results in "repetitive" glare. There are sound arguments for supposing that a certain amount of direct light from widely spaced units is less distracting from repetitive glare. Opinion is still divided as to which of the two methods result in better lighting.

Recommendations Of MOT Committee

Mounting Height

The advantage of mounting height of the lantern lies in the broadening of the bright area of light on the road and a reduction in glare. To produce a continiously bright traffic lane at a lantern-spacing of 150', the lantern cut-off must not occur before 86°. If the mounting height is halved, the angles would be increased to 88°. Although the angular change is small, the effect on glare is very marked, and low mounting heights demand lantern distributions which produce excessive glare.

For cut-off fittings with a cut-off at 70° and a mounting height of 25', the spacing in each traffic lane should not exceed 90'-100'. if the mounting height is halved the spacing should be halved and the arrangement is uneconomical.

At the same time it has been necesary to fix a height at which the lantern can be serviced from a tower wagon and 25' was chosen as the best compromise.

Spacing

As the spacing is increased, it becomes more and more difficult to avoid dark areas beyond each unit, and if attempts area mdea to correct for wide spacings in the lantern distribution, excessive glare often results.

Overhang

Overhang of the lantern from the kerb is provided to enable the patches of light from the lantern to fall on the road. The amount of overhang required depends upon the average width that can be assumed for the bright patches of light under normal conditions of service. The report states that if the spacing between the rows of lanterns exceeds 30', dark areas appear down the centre of the road, and if the lanterns overhang the kerbs for more than 6', similar dark areas appear down the kerbs. On roads 30' wide, no overhang is recommended; on roads 35' wide, 2'6" overhang is required; and on roads 40' wide, 5' overhang. On roads of greater width than 40' an additional lantern must be ung in the centre at intervals not exceeding three spans.

Siting

Central suspension is not advisable except (a) where the road is narrow and fronted by light coloured buildings and (b) where trees on either side make normal side mounting difficult. Widely spaced non-cut-off fittings centrally mounted above a road result in a very bright central lane of light and undesirable dark areas near the kerbs.

For similar reasons, single side mounting is not recommended, except at bends.

Side mounting is recommended. Staggered has lanterns placed on alternative sides of the road with a maximum spacing of 300'. For wide roads, an additional lantern is advised supsended centrally above every third space. When a higher standard of lighting is required, double side mounting is recommended with the lanterns mounted in pairs, one on either side of the road, and spaced 150' apart, again with occasional central units for wide roads.

The treatment of curves is for single side mounting with the lanterns on the outer radius. The lantenr spacing must be reduced in most cases from 150' to as short as 50'-60' on sharp bends.

For cross roads and T junctions the lantern placing is recommended as per the specification. For cross roads, one lantern is placed beyond the crossing and in the trafic lane of the cars approaching the corner. For T junctions, one lantern is put at the end of the branch for cars approaching the main road, and one on the main road beyond the road entry for traffic approaching the branch road on the main road.

Power Of Lanterns

The power of the lanterns has been expressed as the light output of the combined lamp and lantern per 100' run of road. A value of between 3000-8000 lumens per 100' is stated to be satisfactory for roads up to 40' in width.

This method of defining the required luminous output leaves a perfectly free choice as regards the type of light source used. However, the part that the recently developed electric discharge lamps have played cannot be passed over, for it is without doubt due to the efficiency of these lamps and the attention to lantern design that followed their introduction, that we owe the present interest and extent of road lighting.

Distribution

The report makes makes very little reference to lantern distribution other than recognise the cut-off and non-cut-off types.

Next to correct siting of the lanterns, the light distribution is the most important factor in good street lighting.

The correct sharing of light between the road surface and other backgrounds, the careful control of the light over the critical angles that affect glare and the general shape of the distribution curve to produce an even road brightness are all factors of exceptional importance.

In avoiding a decision on this question, it appears that the Committee have been influenced by two factors: (a) Without good siting not even the best lantern will give a uniform background brightness; (b) It would be difficult, with the varying conditions of road surface and brackground to reach agreement as to what constitutes a satisfactory distribution.

Glare

Glare is due to high intensities at angles approaching the horizontal. The report attempts to control this by stating a maximum ratio between the light intenstiy at its peak and the light intenstiy between 30° and 45° to the vertical. Most mordern lanterns meet this requirement with little difficulty and it appears that the recommendation was framed to prevent the excessive glare from lanterns at lower mounting heights and the widely spacing which attempts to throw light to the base of the next standard.

Effect Of The Nature And Conditions Of Road Surface

It is clear that the optical properties of the road surface are of paramount importance in road lighting. The report recognises that road surface materials are governed by non-skid and economic factors. Some ideal requirements as regards the optical qualities from the lighting engineer are:

• That the surface should be semi-matt and light in colour.
• Resistant to the polishing action of traffic.
• Generally similar throughout the country.
• Not markedly changed by resurfacing.
• Having the minimum difference between dry and wet conditions.

Dual Carriageways

Experience is now being gained on the lighting of this type of roadway.

The number of glare points is doubled for a given road brightness and added to this the increased number of units may cause confusion as to the direction the road is taking. There are therefore special difficulties that call for the most careful attention to lantern distribution and siting.

Unidirectional lantern distribution has been suggested but difficulties arise at road junctions, crossings and bends. Some reduction in light in one direction may be possible and the report recommends that this should be investigated. Otherwise the lighting recommended follows the general principles for normal roads, each carriageway being treated separately.

References:
[1] Specification No. 307, British Standard, 1931
[2] Departmental Committee On Street Lighting Final Report, Ministry Of Transport, 1937

A. C. Randle, C.Eng., M.I.C.E., F.I.Mun.E, M.I.H.E, Borough Engineer and Surveyor London Borough of Hounslow

The Association of Public Lighting Engineers Midlands Section

Keywords: Lighting: Lamps, Lighting: Distribution, Lighting: Control, Lighting: Luminaires and Lighting: Theory.

25th October 1974

Abstract: Description of the new catenary street lighting system installed on the A4 in 1974.

Luminaires: Philips ????

The entire paper can be downloaded here.