"David Hearn" wrote in message
...
We have a 300W halogen up-lighter with built in dimmer. It also has a 50W
bendy spotlight with dimmer.

I'm aware that 300W is a lot of electricity, and in fact, it's too bright
when on full - we tend to have it on 50% or less.

Does dimming a light reduce the electricity usage? Part of me says yes,
but another part of me is less sure.

I'm thinking yes - after allowing for triac voltage drop - though it
wouldn't be directly in proportion to the reduction in light because
incandescent lamps are less efficient at low power (and below their design
current ? ).

..