[wizzwizz4]

In real life, a logarithmic brightness scale (which is how human perception works) goes from negative infinity (zero energy) to positive infinity (infinite energy) – excluding both endpoints. 0 is not the bottom, and 100 is not the top.

In real life, photographs are printed on paper. The brightness of light reflecting off paper depends not only on the colour of the paper, but on the brightness of the illumination. (Likewise, photographs displayed on a computer monitor depend on the screen's brightness.)

In real life, human brightness perception depends on the brightness of the environment. An LED can look bright in the dark and dim in sunlight, and range dim to medium to bright on a cloudy day without anyone really noticing that the clouds between them and the sun are thicker or thinner.

In real life, there is no 0. There is no 100. Your comment doesn't make any sense.

[unfocussed_mike]

Right. Metering is even now with scene programs and AI still basically a complicated negotiation about establishing middle grey -- when there may be no perceptual middle grey in the scene at all (black cat in coal bin, polar bear in snow)

The narrow band of sensitivity of a film or sensor has to be sort of moved to where it is needed (by controlling how much light gets in or for how long) according to the result the photographer is likely to want from their photo.

Even the most basic of film dead-reckoning methods -- Sunny 16 -- relies on subjective input from the photographer:

https://en.wikipedia.org/wiki/Sunny_16_rule

And it's up against the nature of human perception of light and dark, which as this classic page demonstrates, is complex:

https://scienceinfo.net/video-chessboard-illusion-confuses-p...