FLUORESCENT LAMP ILLUMINATION CONTROL
Original Publication Date: 1985-Oct-31
Included in the Prior Art Database: 2004-Apr-04
Xerox Disclosure Journal
Figure 1 discloses a circuit used to monitor and control the light output of a fluorescent lamp 10 powered by power supply 12. A controller 16 responds to a signal provided by photodetector 13 or lamp arc voltage monitoring circuit 14 and controls the mercury vapor pressure within the fluorescent lamp via a temperature altering mechanism 18 attached or adjacent to the lamp. In the case when the fluorescent lamp is operated at a sufficient power level to assure operation above its optimum operating temperature for maximum light output, the temperature altering mechanism cools the surface of the lamp to maintain the optimum vapor pressure. Typically, this lamp surface temperature is approximately 35 degrees centigrade. The cooling mechanism is control led by the controller circuit which implements the control algorithm shown in Figure 2. Both the visible light output and the lamp arc voltage are "peaking" functions (maximum at only one point and lower and decreasing monotonically away from the peak value). The lamp arc voltage is useful because it peaks at approximately the peak visible light output of the lamp and therefore can be used in lieu of the light output signal. This is important in applications where sensing the light output is not practical. The lamp arc voltage could be sensed internally in the lamp power supply and therefore has the advantage of no external sensing components.