Quote Originally Posted by wiltw View Post
Not sure why the K values are an order of magnitude different between what you mentioned vs. the K factor in the ISO standard, but since yours expressed no units, that might be the source of the discrepancy.
It is. 1.16 cd/ft^2 = 12.5 cd/m^2 1.30 cd/ft2 = 14.0 cd/m2

I like to use cd/ft2 because it is also the multiplication factor for K in the equation A^2 / T = L*S / K.

256 * 1.16 = 297
256 * 1.30 = 333

256 comes from f/16 or 16^2 which is what the luminance theoretically would be for statistically average conditions if there were zero light loss in the lens' optical system and if the meter had a perfect spectral response.