Equivalent circuit of vapor lamp which typically equipped with ballast is series RL, therefore there are not any importance difference between two circuit analysis. Meanwhile note to following additional information about flicker and effects of voltage quality to its amount. Flicker can be separated into two types: cyclic and noncyclic. Cyclic flicker is a result of periodic voltage fluctuations on the system, while noncyclic is a result of occasional voltage fluctuations. An example of sinusoidal-cyclic flicker is shown in Figure below. This type of flicker is simply amplitude modulation where the main signal (60 Hz for North America) is the carrier signal and flicker is the modulating signal. Flicker signals are usually specified as a percentage of the normal operating voltage. By using a percentage, the flicker signal is independent of peak, peak-to-peak, rms, line-to-neutral, etc. Typically, percent voltage modulation is expressed by 
The frequency content of flicker is extremely important in determining whether or not flicker levels are observable (or objectionable). Describing the frequency content of the flicker signal in terms of modulation would mean that the flicker frequency is essentially the frequency of the modulating signal. The typical frequency range of observable flicker is from 0.5 to 30.0 Hz, with observable magnitudes starting at less than 1.0 percent. The human eye is more sensitive to luminance fluctuations in the 5- to 10-Hz range. As the frequency of flicker increases or decreases away from this range, the human eye generally becomes more tolerable of fluctuations. One issue that was not considered in the development of the traditional flicker curve is that of multiple flicker signals. Generally, most flicker-producing loads contain multiple flicker signals (of varying magnitudes and frequencies), thus making it very difficult to accurately quantify flicker using flicker curves.