wrote

Correct. A dirt-cheap 1N5404, hidden inside the switch. Half-wave
rectifier properties etc. have already been mentioned.

I thought it was a neat trick. A resistor achieving the same thing
would have to be of the order of 17W or so.

BTW neither the people who sold the lamp nor the experts in the two
specialist electrical shops knew the answer.

Michael Koblic,
Campbell River, BC

There's an old parlor trick with two switches and two bulbs wired in a
series loop where each switch controls a bulb independently.
http://img517.imageshack.us/img517/7...circuit1tb.jpg
http://img291.imageshack.us/img291/1263/circuit25jw.jpg

You build it with porcelain-base knife switches and lamp sockets each
on a separate small wood block, connected with a single strand of
solid or clear-insulation speaker wire.

With both switches open, both bulbs are off. Close either switch and
its bulb lights even though the other switch is plainly open -- that's
the reason for using knife switches. There is enough open space under
the porcelain base for the diodes, which the wood blocks keep
concealed. Don't show it to technicians who might carry screwdrivers
(like me) and ask to disassemble it.

No one ever notices that the bulbs aren't at full brightness.

I don't have a photo of mine, I took it apart because it is so
dangerous.

jsw