[adam2]

VERY old d0m3stic dimmers, and indeed theatre dimmers, did indeed dim by varying a resistance in series with the lamp.
However for AT LEAST 40 years, theatre and d0m3stic dimmers have used semiconductors to chop the waveform.
They therefore use similar principles, theatre dimmers are normally of larger capacity, remotely controlled, and better suppresed, but contain the same basic circuit.

A d0m3stic resistance dimmer for a load of a few hundred watts would be a bulky item since it would have to disipate 100 watts or more, it certainly would not fit a standard mounting box.

Resistance dimmers are not much used these days

This post has been edited by adam2: 04 February 2012 - 03:46 PM

[bigclive]

The basic 1W mains LED lamps generally use a very minimalist capacitive dropper where a resistor and capacitor are put in series with a rectifier, with the LEDs across the output of the rectifier. For normal use this is acceptable, but when dimmed the whole circuit turns into an interference suppressor with every single switching point in the dimmed waveform resulting in a spike of dissipation in the circuit. This usually kills the series resistor or LEDs quite quickly.

[ojc123]

adam2, on 04 February 2012 - 03:45 PM, said:

VERY old d0m3stic dimmers, and indeed theatre dimmers, did indeed dim by varying a resistance in series with the lamp.

Indeed. In the late 80's our school installation still had open wire-wound rheostats which were patched in to each circuit to dim it. (There were only four rheostats for twenty four circuits.) These were from the original 1956 installation. They did get VERY hot and they could give the user a bit of a tingle because they weren't earthed and the system was very poorly maintained. I called up the safety elf who waved her wand and got rid of them in short order.

[dbuckley]

Do I have to post that pciture again?

[matt c]

Go on, Mr. Buckley... You know you want to...