Logarithmic response of the eye?

Question

I've heard that the eye responds logarithmically to a luminescent source, ie, multiples of intrinsic brightness are perceived as equal intervals of brightness. One source said this is a misconception - who is right?

Answer 1

The response of the eye was at one time considered to be logarithmic.  However, now the response is believed to follow a power law.

Br = k*I^a  where Br is apparent brightness and I the source intensity, k and a are constants.

The value of the power a and constant k are different for different types of sourcesand conditions.  For more information on this see

http://en.wikipedia.org/wiki/Stevens%27_...

Apparently the situation is not a simple one and there is still some dispute in the matter.