It depends on each lamp. The amount of displacement power factor is negligible for all types, but the distortion power factor can range from about 0.5 to near unity. Dimmable ones usually have less THD. If you understand how standard dimmers work, you'll see that a common peak-drawing type front end wouldn't work. It does not car about how far you delay the power on is, because rectified power factors naturally have a turn-on delay pretty close to 90 degrees.
It works like an extremely fast clutch. Imagine you're rowing a boat. A resistive loads load it evenly across the entire stroke. A dimmer adjusts the power by always starting unloaded as you row, then decides when to load the oars. A rectified load don't load at all at the beginning, then loads the oars VERY heavily during a short range abruptly, then drops the load very abruptly.
For a dimmer to work it has to be similar to linear load or it will just ignore the power and use its own "clutch" to notch load.
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