I would like to get an estimate of original scene luminance from exposure data.

ISO = 250
Shutter speed = 1/640s
Aperture = f/10

Calculated EV = 15.97

I use this set of equations : https://1drv.ms/u/s!AkD78CVR1NBqlssbPh7nK5zxJRZv5A?e=wwIoKc
Where S = ISO, L = Luminance, K = Camera constant = 12.5
N(square) = Aperture and t = Shutter speed (exposure time)

Luminance = 3200 Cd/m2

Does that make any sense?