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In article .com,
writes:
I pretty much agree. But let me add for the sake of pedantry also that
one can dim standard cfls to a limited extent by reducing v_supply, and
reducing v_supply could be achieved by a phase chopping dimmer, though
_not_ the normal pahse shift ones sold for use with incandescents.
Instead it would need to switch o/c during mains v_peaks to charge the
cfl reservoir to lower v. Which implies something other than a triac
for control. But... IRL one would not use that approach.

I've tried reducing the voltage at the reservoir capacitor, and
it doesn't work. The electronic control gear still feeds the
lamp with constant current over a wide voltage range and so no
dimming happened. When you go outside this range, very strange
things happen. With one lamp, reducing below the threshold
where the control gear could generate constant current, the
current must have increased dramatically as the lamp suddenly
got much brighter. It would likely destroy itself if run this
way for any length of time.

If you remove the reservoir capacitor, the lamp gets dimmer as
you would expect because it's now flickering at 100 times/second
(although not percetably). If you then connect such a lamp to a
phase control dimmer, it does dim over a reasonable range, but
obviously you can't get it to full brightness.

--
Andrew Gabriel