Chris Lewis wrote:
According to lee h :
franz frippl wrote:

Dimmer switches are no more than rheostats. If carbon were to build
up on part of the switch, it may be sufficient to affect voltage.
Might cause a voltage drop.

You could test this with a volt/ohm meter.

In ye olde days, you were right. However for many years,
the triac-based dimmer switch has been the more common.

"More common"? Even in ye olde days, rheostat dimmers were extremely
rare, and they're now essentially non-existant.

Chris, I suspect that your definition of 'ye olde' and 'many years'
is more short term than mine. The SCR which enabled solid-state
control of dimmers was not invented until the late fifties. Rheostat
dimmers and auto transformers (Variacs) were the *only* means of
dimming lights until then. So they were hardly rare. Solid state
dimmers were not commonly used in homes until the late
sixties. But, you are right about the rheostat dimmer's heat
output. Most were mounted in a box on the outside surface of
a wall, not in a switchbox.