Incandescent Lamp as a Control System Element

Three tungsten‐filament lamps have been investigated with particular attention given to determining the applicability of the standard linear transfer function concept to these basically nonlinear elements. The lamps cover a power range of from 14 mW to 14 W. They are the Kay L12–12 Pinlite, 12 mA at 1.2 V, the No. 47, 150 mA at 6 V, and the No. 94, 1.2 A at 12 V. The greatest range of operation linear to within 5% is determined from output luminous flux versus input voltage characteristics. Allowable flux variation about a dc bias point selected in the 5% linear range is found to be at least ±40%. Bode type amplitude‐phase characteristics are measured for the three lamps. Conventional linear transfer functions are deduced from the Bode plots, linear approximations are constructed, and the resulting composite approximations are compared to the empirical characteristics and found to be satisfactory for design usage. Deviations from linear operation are investigated, and in the case of the lamp bias, found to impose some restrictions. An operating lamp control system designed on the basis of the above described work has been built and is discussed.