Electronic Ballast
Revised: September 18, 2012 3
The electric behavior is simple. The lamp current is determined by the applied voltage and by the resistance of the tungsten filament. It is close to the v-i characteristic of a linear resistor. The spectrum of energy radiated from incandescent lamps is continuous with good color rendering. However, only about 10% of the electricity flowing through incandescent lamps is converted to light, as shown in Figure 2(a), and thus the luminous efficacy of incandescent lamps is low. Electric gas discharge lamps convert electrical energy into light by transforming electrical energy into the kinetic energy of moving electrons, which in turn becomes radiation as a result of some kind of collision process. The primary process is collision excitation of atoms in a gas to states from which they relax back to the lowest-energy atomic levels by means of the emission of electromagnetic radiation. The emitted electromagnetic radiation is not continuous, instead consisting of a number of more or less separate spectral lines. By modifying the composition of the gas used, the luminous efficacy can be varied considerably.