can someone explain the candela a little?

this is more of a question regarding what might be considered fundamental
dimensions of physical quantity. assuming we can stay away from the issues
of whether or not the speed of light is dimensionless (since it is defined)
and the equivalent question of whether energy and mass are the same
dimension of quantity (let's say they're not, for this case).

as i read the SI definition of the unit of luminous intensity, the
"candela", it seems to me to be equivalent to power:

"The candela is the luminous intensity, in a given direction, of a source
that emits monochromatic radiation of frequency 540 x 10^12 hertz and that
has a radiant intensity in that direction of 1/683 watt per steradian."

or a candela is simply 4*pi/683 watts.

but how does the frequency of radiation figure into the definition of
luminous intensity? if the radiant intensity was 1/683 watt per steradian
and the frequency was 1080 x 10^12 Hz, would the quantity of luminous
intensity be 1 candela? or 2 candelas? or something completely different?

i understand blackbody radiation and the whole bit, i just have trouble with
the definition (and wonder why there is a separate definition of luminous
intensity in modern times, anyway).

--

r b-j rbj@xxxxxxxxxxxxxxxxxxxx

"Imagination is more important than knowledge."

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