GROUP "AL" & "A" TWIN LAMP

The reflectors consist of one piece castings glazed with silvered glass facets, cut from flat sheet, embedded in a special atmospheric resisting cement. Each facet is set at the exact angle and is of a calculated size to produce the desired light distribution.

Material: Cast iron or Aluminium non-corrosive alloy.
Finish: Green or Aluminium. Other colours to order.
Tapping: ¾" gas thread as standard. Tappings to 1¼" to order.
Lamp Holders: Bayonet Cap or Edison screw. Anti-vibration B.C. type as standard. Rigid Edision screw or rigid Bayonet Cap when specified.

approximate dimensions and weights

The reflectors are designed to produce a light distribution of the required characteristics to ensure good uniformity of illumination and road brightness. The peak candle power is projected at an angle of 10^o below the horizontal.

The recommended average economical spacing of posts is ten times the mounting height of the lamp filament.

Type of lamp. B.S.I. type clear gas filled singled coil tungsten filament lamps for standard use. Where the reflectors are installed under aderse circumstances as regards mounting height etc., pearl lamps may be used as explained later. Also, where coiled coil lamps are employed, these should always be of the pearl type unless the mounting height is more than 17'.

The particular advantages of the Twin Lamp construction are:

1. Additional safety against lamp failures. If one lamp fails the light from the remaining lamp will be sufficient until the faulty lamp has been replaced.
2. Under certain circumstances the lamps may be connected to different supply circuits thus reducing the risk of complete failure due to a local supply fault.
3. The lamps may be connected so that one lamp is disconnected at midnight or other desired time. The remaining lamp need not be the same wattage as the first lamp as the lamp position can be pre-set, at a slight additional charge, in accordance with the light centre length of the lamp.

The table below gives the suggested mounting heights for various wattages. Where the mounting height is less than these values, it is advisable to either use pearl lamps or one of the numerous grades of semi-diffusing silvered glass instead of the clear mirror glass. Reflectors glazed with different grades of this glass may be loaned for trial purposes and the grade best suited to the conditions can then be chosen.

angular settings

The table overleaf indicates the present range of angular settings, but we make a regular practice of designing special patterns whenever we find unusual positions.

The angles are read in a clockwise direction looking down on the fitting. It must be remembered that the angle of the reflector does not follow the angle of the road. For instance, in the case of a straight road with side of road mounting, 180^o reflector is not required, the correct one being usually 165^o or 170^o. (i.e. ensuring that a minimum of light is wasted on the boundaries of the road.) Another example is an exact 90^o sharp bend; here either a 100^o or an 80^o fitting will be necessary according to whether the post is on the inside or outside of the bend. The general lines of procedure are described in the introductory matter of our general catalogue.

It will be seen that two types of reflectors employing two lamps are tabulated under the Group "A" size, the Two Light and the Twin Lamp. In the case of the Two Light the lamps are normally arranged in line with the length of the road and with the Twin Lamp they are arranged transversely.


technical service

The personal services of our technical staff at the works are at our clients' disposal at all times. They are prepared to visit a district in order to advise on all street lighting problems, also to inspect every individual lighting position to ascertain the correct reflector, or this latter work can be done reasonably well from plans.

They are also ready to carry out photometric tests on site, for which purpose they are equipped with the latest portable photometers available.

schedule of angles