Andrew Gabriel wrote:
In article ,
"ian field" writes:

In countries with different mains voltage, the ratio may need
adjusting, as filament lamp efficiency varies with the design
voltage. (The most efficient voltage to design a 100W lamp is
about 55V, given a reasonable life requirement, and as you move
the design voltage away from 55V in either direction, the lamp
efficiency drops.)


Interesting. I can see it dropping due to conduction losses when the
voltage gets too low (so that the wire gets too fat) but what's the
mechanism for the drop-off at high voltages?

Cheers,

Phil Hobbs