Dimmers for tungsten lamps

The advent of tungsten lamps for theatre lighting made necessary a complete re-design of the dimming apparatus. Dimmers designed for the control of carbon filament lamps do not give smooth and flickerless regulation when used with equal loads of tungsten lamps. This is due to the temperature coefficient of resistance of the lamp filaments, that of the carbon filaments being negative, and that of the tungsten filaments positive. Curves are shown to indicate the change in lamp resistance and candle power for various watt inputs. Curves for both carbon and tungsten filament lamps are shown in order to bring out the contrast, and a method described for determining the resistance per step and number of steps in the dimmer designed for control of tungsten lights. Following is a brief indication of commercial requirements in dimmer design.