I have a bedside lamp with a 100W halogen lamp which runs directly off
110V. In the base of the lamp is a small rotary switch about 3/4" in
diameter. It has three positions: Full intensity, reduced intensity
and off. No other parts are discernible.

The question is: How does the lamp achieve the reduction in light
intensity (about half)?

I actually know the answer because I took the switch apart but when I
was looking for it before on Google etc. I could not find it.

I am posting here to see how widely this trick is known.

Oh, and the lamp is *metal*.

Michael Koblic,
Campbell River, BC