"Paul Hovnanian P.E." wrote in message
...

What sort of 'dynamic range' do these things have? How close to zero
output can the lights be set? On the other end, how close to 100%?

Variac control can go from 0 to something over 100% (I have one with a
110% tap).


Reactors and rheostats were both an impedance that was inserted in series
with the lighting load. They had some severe limitations in how they could
be used and the useful dimming range that could be achieved. When the Variac
(originally trademarked by General Radio, 1934-2002 ) came out, it was
almost immediately accepted as the preferred means of dimming. The Variac
was still preferred for dimming in the early days of SCR dimmers for a
couple of reasons. Early SCR dimmers simply were not robust enough for live
use. When a lamp blows, the filament vaporizes and for an instant, a low
impedance arc forms. That often draws enough current to cause a SCR to short
out. The other reason was the nasty risetimes that were both radiated from
all wiring and coupled back to the line... all of which wrecked havoc on
live sound systems. I spent way too much time trying to phase the lines and
lifting/moving grounds on the sound systems to minimize buzz from the
dimming systems.

btw- I remember seeing ganged Variacs that were motor driven to dim very
large loads like the theatre house lights. Was neat at the time to have
pushbutton dimming (two buttons: one for dim/down and the other for
brite/up)

Oppie