Daylight at Night
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in P .S.V .s
IN Sweden, fluorescent lighting for buses and coaches has been the accepted standard since 1939 and it is found in the fleets of more than 50 operators. The credit for this achievement must go to Graham Bros. A.B., Stockholm.
Martindale Electric Co., Ltd., Westmoreland Road, London, N.W.9, holds the manufacturing rights of the Graham lighting system for Britain and the Commonwealth. At a recent demonstration, a representative of "The Commercial Motor ". was able to examine the.possibilities of the system for British operators.
The Graham system is of the coldcathode t9pe. The tubes are insensitive to cold and ignite immediately the current is switched on. The level of illumination obtained is claimed to be five times greater than that yielded by an equivalent filament lamp and is completely free from glare. The coldcathode tube provides a lower intensity of light, but a better spread than the hot-cathode type.
Power from 24-volt vehicle batteries is converted to a.c. by a small vibrator which weighs only 12 lb. The current is then stepped up to 3,000 volts by a pair of transformers and a condenser, which together weigh 34 lb. In a normal vehicle lighting set, six 50-watt tubes are employed, arranged to form two sets of three tubes each, wired in paralLelS Two small tungsten regulator lamps are in the I.t., a.c. line. A lighting intensity of 31 lumens per watt is claimed, for a consumption of 12-} amps. Thus, assuming an efficiency of 80 per cent, per tube, a lighting intensity of 9,600 lumens is possible per vehicle for the same current consumption as the normal filament lighting arrangement. Any length of tube may be specified, but as the efficiency of the tube increases with length, 6-ft. or 9-ft. units are normally employed. When fitted in a bus body, pairs of tubes may be joined together to form a continuous strip, with connecters at the adjoining ends.
The tubes may be bent to any desired shape, and although normally mounted behind translucent plastic shades, they may be completely enclosed behind the body panelling or in the roof.
Great care has been taken in the design of the fittings to ensure complete safety. The contact holders are made of Melamin and the contacts themselves are arranged to cut off the current if any part of the tube is tampered with, or if a tube is accidentally broken when illuminated. The tubes themselves are mounted on felt packing, but are little affected by vibration. The manufacturers claim a life of 10,000 hours for both the tubes and the vibrator. The last-named has replaceable contacts and can be reconditioned cheaply. The tubes give a constant light and do not flash if the current varies.
Shadowless Lighting Wiring is facilitated by the small number of contacts required and the shadowless lighting obtained is soothing but highly efficient. It is possible, if required, to tap the transformer so as to provide half the normal current, and thus reduce the intensity of illumination, a useful point for night-service coaches.
Because no heat is given off by the tubes, condensation is eliminated, as is discoloration of the panelling.
Although the cost of equipping a double-decker might be in the region of E80, the cost of maintenance, replacement and cleaning is negligible.
For night service vehicles, the ability to reduce the intensity of lighting is important, especially as the colour of the light is unchanged. Moreover, the vibrator can be used to provide power at suitable voltage for electric razors and other equipment.