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306
BOURNE AND BEESON
September
Y* 2000
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3 10 5 0 5 10 IJ DIVERGENCE 6°
Fig. 5. M-R 356 Cine Flash polar distribution; lamp operating at 1 kw, measured at 10 ft with normal diffuser, 18,430 lumens from each lamp.
is pressed a red warning lamp lights up to indicate that the lamp is being overloaded.
The light output from a discharge lamp follows changes in the current through it almost instantaneously. For example when a compact-source lamp operates on alternating current at 50 cycles/sec, the light falls to 4% of the maximum at the end of each cycle. In order to prevent cyclic changes in exposure of the film it is therefore necessary to operate the lamp on a smoothed d-c supply and the ripple voltage should preferably not exceed 10% of the supply voltage.
The control unit is designed normally for operation from a 200to 250-v d-c supply. When no d-c supply mains are available, the equipment must be operated either from a three-phase rectifier unit or from a mobile d-c generator.
OPERATION OF THE EQUIPMENT
The first type of equipment to be built consisted of a control unit with one lamp head. This equipment was demonstrated at the Royal Photographic Society on January 13, 1949, and subsequently at the British Kinematograph Society. Generally, however, two light sources are necessary for photography to obtain the necessary light distribution and modeling. Later equipment was therefore redesigned to operate two lamps in series with a single control unit thus enabling the light output to be doubled for the same current from the supply.
A mains voltage selector link on a panel at one end of the control unit is provided for setting the equipment for the particular supply voltage which can be read on the panel voltmeter. This ensures that