mcds

[Ray Rogers]

Does anyone know offhand if mcds are a purely physical measurement...
or, a psychophysical measurement?

I think its the former but want to double check.

Ray

[David Grenet]

Somewhere in between. The measurement is weighted by a model of the spectral response of the human eye, so it depends on colour.

http://en.wikipedia.org/wiki/Candela

[Ray Rogers]

Thanks.

Guess I'm a bit confused about how light meters work...
are those readings also biased in favor of human vision?

If you illuminate a subject in green light vs Blue or Red, is there an intentional bias in the meters logic?

What is the purely non-psychophysical measurement of light for photographic purposes?

[ic-racer]

1⁄683 watt per steradian of green light is pretty much set in stone since 1979. It is a purely physical measurement.

[Ray Rogers]

1⁄683 watt per steradian of green light is pretty much set in stone since 1979. It is a purely physical measurement.

Does that 1⁄683 watt per steradian apply to all wavelengths?

[Chan Tran]

Does that 1⁄683 watt per steradian apply to all wavelengths?

No. only visible light which is peaked in the green.

[Ray Rogers]

Ok, so the different wavelengths are weighted differently... in mcd;

Jumping from mcd to photographic light meters, is this also true of light meters?

or do they use a purely physical measurement?