There are many fixtures that would not accept the older CFLs without some modification. You may remember the hoop extenders that were included with some of the early CFLs. Most of today's commodity CFLs are physically much smaller with bases similar in size to equivalent incandescent bulbs.
Low power factor results from a capacitor-input power supply that is only drawing current near the peak of the waveform (which also happens to be away from where X10 signals are transmitted). The small bases used in today's CFLs make it impossible to squeeze in the 175V+ electrolytic capacitor required for direct line rectification. So these newer units use a switching pre-regulator on the raw rectified AC input. That pre-regulator runs essentially over the entire waveform, resulting in a much higher power factor (and also noise radiated in the X10 transmission window).
I'm amazed how cheap semiconductors have become. It may very well be cheaper to use a switching pre-regulator than the large high-voltage electrolytic capacitor needed for direct line rectification. The XTB filter capacitor costs almost twice as much as the high power MOSFET used in the transmitter output stage. It wouldn't surprise me that the pre-regulator design actually costs less. And the smaller physical size means a larger potential market for these commodity CFLs.
Jeff
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