The British Standards Instituion has issued a specification for Street Lighting No. 307/1931, wherenin 8 classes have been specified, with a minimum illumination mounting height and recommended spacing to height ration for each as follows:-

A further specification No. 398/1930 has been issued classifying the symmetrical light distribution from Lighting Fittings. Street Lighting Fittings under this Specification fall in the class specified as "Direct," and shall give not less than 90% of the total flux in the lower hemisphere. The classification of the general character of the polar curve is divided into five classes:

When applicable, the classification and frame ratio in accordance with this specification is given with the illustration of the fittings it applies to. The operation of the inverse square and Cosine laws of illumination so reduce the intensity of illumination at the region midway between two units compared with the intensity in the region of the sources that for economic reasons a disparity has to be tolerated.

The Designer of equipment and the installation Engineer's aim is at the minimising of this disparity.

It must be recognised that any attempt to raise the midspan illumination at spacing height ratios beyond those recommended in the specification will lead to inferior visibility owing to glare from the successive units. The PATENT LENS DOME REFRACTOR (Patent No. 373399), manufactured specially for us by Holophane Ltd., has been evolved after due consideration of these factors. The distribution is symmetric, diametrically or divergently opposed according to type, and this directive control combined with the large zone of collected emission from the light source equips these refractors with a exceptionally high utilisation factor, the resultant illumination being graded from maximum to minimum with an unusual uniformity, the magnification being well dispersed laterally to cover the road width. In the angles between 75 deg. and 90 deg. to the downward vertical, the luminous intensity is progressively reduced to such proportions that glare becomes an impossibility.

The range of our Refractor Fittings is equipped to suit all probable requirements, and the advice of our Technical Experts is available without obligation.

In this particular section is illustrated a series of fittings and equipment, the accurate formation of which is the result of many years' research work and manufacturing experience, being specifically produced to meet the various conditions that scientific consideration demands.

Special attention, as mentioned above, has been given to the avoidence of glare, the ruling principle being, the greater the intrinsic brilliancy of the light source, the more remote must it be from the range of normal vision.

The conditions call for the directional control of the light rays at source by means of reflection, refraction and diffusion, and it is by specialised knowledge and experience that we are able to produce the necessary apparatus to efficiently accomplish this.

The general design and constructional details of the apparatus illustrated are of robust character, special attention being given to all the features operating for hte best in service, ease of installation and economical maintenance; many of these, being of an ingenious and novel character, are fully protected by Registrations and Patents.

The vitreous enamel is produced in our own Factory by means of the most up-to-date methods and equipment; with constant testing to obtain the finest specular or diffusing reflecting finishes with the hardest wearing qualities.

The range of REVO Patent Magnalite Silvered Mirror Street Lighting Fittings, the demand for which has exceeded our most sanguine expectations, is fully described on pages 94 to 96, 113, 118 and 112, and the extensive selection of Lanterns available for use with Electric Discharge Lamps, both Mercury Vapour and Sodium types, covered by pages 117 to 126 of this Catalogue, are the outcome of scientific research and the adoption of those sound manufacturing principles, which have placed the name REVO pre-eminent in the world of Industrial and Public Lighting Equipment.

From Design, Drawing Office, Experimental Test Room to Production and Depatch Department, the various pieces of apparatus pass in ordered sequence through Pattern Shops, Iron and Non-Ferrous Foundries, Machine Shops, Assembling Bays, Test Rooms etc., until the finished article is ready for despatch. The works being self-contained, all points in the process of manufacture are subject to inspection by special men detailed for this work, ensuring economical, accurate, inter-changeable co-ordinated production and the immediate adoption of any improvements which it is deemed desirable to incorporate either in production methods or apparatus.

For schemes of illumination, where a specially decorative character is desired to harmonise with the surroundings, our artists and craftsmen specially trained for this work are at your service, and we make a speciality of the pictorial illustrations of our proposals, combining the scientific principles so essential to the economical distribution of light with artistic decorative conception.

For Perfect Street Lighting