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1953-54 Theatre Catalog, 11th Edition, Page 101 (67)

1953-54 Theatre Catalog, 11th Edition
1953-54 Theatre Catalog
1953-54 Theatre Catalog, 11th Edition, Page 101
Page 101

1953-54 Theatre Catalog, 11th Edition, Page 101

READING FROM TOP TO BOTTOM IN THE COLUMNS AT RIGHT-Fig. 7 shows the EMS current versus li/XL ratio. Fig. 8 shows the light output versus R/XI. ratio. Fig. 9 shows the conduction angle versus the H/XI. ration. This angle divided by 180 degrees gives the traction of the hall cycle that voltage is applied to the lamp load.

conventional ballasts. The percentage flicker as measured by photo-cell instruments increases as the lamps are dimmed. However, lamp flicker becomes less apparent to the eye as brightness decreases with the result being essentially the same at low brightness on the dimming circuit as conventional operation at full brightness.

The Distribution System

Referring to Figure 10 only three wires are required to bring power from the control unit to the lamp load. A nominal 236 volt single phase line supplies power to the control. One common and one control line are needed to supply voltage for lamp arc current. The third wire bypasses the control to provide the cathode preheat transformers in the ballast With line voltage thus maintaining constant cathode temperature over the dimming range.

The Lamp Ballast

The lamp ballast consists of a series reactor for arc current control and two isolated cathode windings. The lamp load has a power factor of approximately 50 percent lagging. Correction to over 90 percent can be made by placing capacitors across the line on the input side of the control. Approximately four mfd. per lamp will be required.

Characteristics of Dimming System

In order to obtain the maximum range of light output, cathodes must be continuously heated. The instant start lamps such as the slimline group cannot be provided with cathode heat and, therefore, the system was designed for 40-watt preheat lamps only.

Requirements for Starting

It will be noted in the description of Figure 2 that a peak voltage is supplied to aid in starting the lamps. Since the effectiveness of the peak voltage in starting the fluorescent lamp depends on the capacity coupling from lamp to ground, there should be a grounded metal plate near the lamps; for most applications, fixture bodies or wiring channels will suffice. If open wiring on a wood panel is used there should be a one inch metal strip running the entire length of the lamp and placed approximately 3/8 inches behind the lamp. The strip should then be connected to the grounded line wire through a '12 megohm resistor. Under normal conditions the lamps should start quickly and reliably at any point in the dimming range.

Brightness Range

The system provides for relative brightness varying at least 100 to one. Under optimum conditions of line voltage and ambient temperature, and with well Seasoned lamps, the brightness range can be increased to 250 to one. New lamps may not start immediately at the low



;. ecnceur LIGHT O




.9 Lo Ll 1.3 1.3 l.4 l.5 l.6 R/XL or PHASE CONTROL CIRCUIT
1953-54 Theatre Catalog, 11th Edition, Page 101