galleries is sufficient for read- ing, the partial screening effect of the galleries would make it difficult for the Spea. ker to see the faces of Mem- bers occupying these seats. A line of flourescent lamps there. fore runs round all four sides of the Chamber in a recess on the underside of the front of the galleries.
Control of the Chamber lighting is normally effected from the Engineer's Control Room in the basement of the House. Pushbutton witches for remote control of the motor-driven dimmers are mounted on a panel beside the Engineer's desk, enabling the illumination to be in- creased or decreased as necessary. Indicator instru- ments are recessed into the panel to show the intensity of the main ceiling lighting. while coloured pilot lights
show when the lamps under the galleries and in the sills are alight. The Engineer controls other services in addi- tion to lighting, and watches the Chamber through a periscope running up through four floors to a vantage point in the Chamber.
The total number of fittings in the whole installation is over 1,800, and of some 4,000 Osram lamps employed more than £5 per cent are fluorescent,
It is obviously impossible in a publication such as ours to give a complete technical description of the installa- tion, but we do feel that some further details of the Dim- mer Controlled Circuits would be of value not only as an explanation of one of the most intricate parts of the installation, but as an illustration of the difficulties that were encountered and successfully met.
Since only very limited dimming is obtained when one series resistance is used to control several fluorescent lamps, it was necessary to provide a method for varying the current in individual lamps. A separate variable re- sistance could be used for each circuit, but in this instance it would present many practical difficulties, as in the Chamber a total of 243 fluorescent lamps, including bot cathode and cold cathode types, have to be dimmed.
The fluorescent lamp circuits, described later, with the exception of that for the Speaker's chair, include a trans- ductor (or D.C. saturable choke) for each lamp. With this arrangement many lamps can be dimmed together by using one control, such as a potentiometer, to adjust the direct current in the control windings of the transductors. This method enabled a dimmer equipment with a minimum of moving parts to be installed,
The control of the lighting had to be smooth to ensure a steady uniform increase in illumination, and although it was realised that in practice the artificial lighting would be introduced while the Chamber was still partially lit by daylight, it was nevertheless desirable that the lighting should be raised from blackout without any per- ceptible hesitancy in any of the panels. Special circuits and equipment could be used to provide the degree of control of the fluorescent lamps necessary at the lower end of the range, but these were considered to be an unecono- mical proposition. A compromise was, therefore, made using an auxiliary lamp circuit which could be controlled easily from zero.
Two tubular filament lamps are fitted in each of the 150 panels and baffled so that no direct light falls on the glazing. Each lamp is made in А special coloured glass to ensure that the appearance of the ceiling when lighted by the auxiliary lamps is similar to the effect from the fluorescent lamps.
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The method of operation decided upon was for the auxiliary lamps in each panel to be controlled by a vari- able series resistor. When the lighting is required, the auxiliary lamps are switched on in the dim position and the brightness of the ceiling panels gradually increased
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a. the dimmer resistor is slowly cut cut of the circuit. At a ]. redetermined position of the auxiliary dimmer, the cold cathode lamps are automatically switched on in the dim position; the intensity of the cold cathode lamps is then brought up steadily to its maximum.
At first it might be thought that the filament lamps used in the auxiliary circuit would have a short life com- pared with the 10,000 hours life expected from the cold cathode lamps. The dimmer equipment, however, has been designed to cut off automatically the supply to the auxiliary circuit when the intensity of the cold cathode lamps attains abcut 25 per cent of its full value. This means that the auxilia y circuit will be connected for a few seconds only cach time the lighting is used, and it is expected that with this arrangement the useful life of the filament lamps will be very great.
The General Electric Co. Ltd. of England, whose Hong- kong Branch operates under the name of The British General Electric Co. Ltd. of Queen's Building, are naturally intense- ly proud of having been entrusted with one of the most im- portant and historic lighting installations of modern times.
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