On 28 Jan 2006 03:36:25 -0800, wrote:

Victor Roberts wrote:
On 27 Jan 2006 08:40:51 -0800, "
wrote:

There are special dimmable compact fluorescent bulbs, but they are very
pricey. Do these work with regular wall dimming switches? I've seen
suggestions that there are also special dimmers that work with regular
CFL's. Anyone with experience and/or sources for these special dimmers?
I assume its more cost effective to go with one dimmer and the regular
CFL's.

If by "dimmable compact fluorescent bulb" you mean a compact
fluorescent lamp with an integral ballast and an Edison
screw base, and if you live in North America, then the
answer is yes, these are designed to be used with the same
phase cut dimmers used with incandescent lamps. They may not
have the same dimming range as an incandescent lamp, but
that is how they are intended to work.

As for special dimmers for "regular" CFLs." I am a bit
confused. If the "regular CFLs" have integral ballasts and
an Edison screw base, then they cannot be dimmed unless they
are the type described above which are designed to be
dimmed. However, if the lamps do not have integral ballasts
and have instead a 4-pin base then they need an external
ballast and they can be dimmed by using special electronic
dimming ballasts that provide a wide dimming range but are
also quite expensive.

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.

Andrew is correct. Many electronic ballasts include at least
some rudimentary feedback that tries to hold the lamp
current constant when the line voltage varies. These
ballasts will hold the lamp current relatively constant over
the input voltage design range, but their behavior outside
this range depends upon the circuit topology. Some will drop
out completely when the line voltage goes too low while
others may not.

BTW - I have tested some of the relatively new "universal
input voltage" ballasts. The ballasts I tested were listed
as suitable for 120 or 240 volts. These ballasts held the
lamp current constant as the input voltage was varied
continuously from about 90 volts to about 280 volts.
Somewhere below 90 volts they shut down but I don't remember
the exact voltage - but it is in my notes if anyone wants
the exact value.

Considering the large number of different circuits that can
be used for electronic lamp ballasts, it is risky to propose
one solution for operation of these ballasts outside their
design voltage range.

--
Vic Roberts
http://www.RobertsResearchInc.com
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