The High-Reactance Autotransformer Ballast is used when the line voltage in insufficient to ignite the lamp using a reactor type ballast. As a result, these ballasts are bigger, heavier, and less efficient than reactor ballasts, but they can be used in a wide variety of applications, because they come with multitap capability. It is very similar to the reactor ballast, but utilizes a two-coil design to step up the startup voltage to ignite the lamp. The coil then acts to regulate the lamp current similar to the reactor ballast. The High-Reactance Autotransformer Ballast typically has 90% + HPF power factor, and 1.4 to 1.6 current crest factor (CCF). Most HX-HPF ballasts are rated to handle supply voltage variations of 5%, which results in a 9 to 12% lamp power variation.