Calculate here with the details of luminance, effective aperture and shutter speed, ISO sensitivity.
Film speed is the measure of a photographic film's sensitivity to light, determined by sensitometry and measured on various numerical scales, the most recent being the ISO system. A closely related ISO system is used to measure the sensitivity of digital imaging systems.
Relatively insensitive film, with a correspondingly lower speed index, requires more exposure to light to produce the same image density as a more sensitive film, and is thus commonly termed a slow film. Highly sensitive films are correspondingly termed fast films. In both digital and film photography, the reduction of exposure corresponding to use of higher sensitivities generally leads to reduced image quality (via coarser film grain or higher image noise of other types). In short, the higher the sensitivity, the grainier the image will be. Ultimately sensitivity is limited by the quantum efficiency of the film or sensor.
Source: Wikipedia.de, Keyword "Film speed", Version from 01.12.2014 16:02 Uhr, Link
H = (b ⋅ L ⋅ t) ÷ N2
The factor b = 0.650 arises from the physical properties of the lens (lens transmission, vignetting and stray light factor), an object distance of 80 times the focal length and an angle of 12 ° from the lens axis (ISO measurement protocols)
Here you can calculate between the different sensitivity units.