Fluorescent lamp cold environment performance improvement

Abstract

Three approaches to improving the efficacy and start-up time of commercially available cold cathode fluorescent lamps under cold ambient conditions are evaluated in this paper: heating the tube on one side; heating the tube on two sides; heating the circumference of the outer tube. The internal power density generated by ion bombardment of the cathode and collisions in the plasma is indirectly obtained by matching simulated axial wall temperatures with those obtained by experiment at room temperature. The estimated power density is used to evaluate the temporal evolution of the axial surface wall temperature under different ambient conditions immediately after a cold start. All simulation results have been obtained using PHOENICS, a computational fluid flow program. Experiments have shown a good correlation between the time taken for the light output to reach an acceptable value and the time taken for the inner tube cold spot to reach a temperature of 0/spl deg/C. These results have been used to estimate heating time for different heater geometries and heater powers. The study shows that the conduction of heat to the outer glass envelope is the limiting process that controls the start-up time. Modest improvement in start-up time can be achieved by increasing heating power or by moving the heater to the side of the lamp. However, only a heater which entirely surrounds the lamp is capable of substantially decreasing the start-up time.