All explained there: https://en.wikipedia.org/wiki/Gamma_correction
TL;DR: our eyes are non-linear sensors, in linear light, half the possible values are wasted to encode 20% of the vision range. Sustainable if you have a lot more levels that the eyes can sees (16-bit or more), not sustainable if you barely have enough (8-bit).
TL;DR: our eyes are non-linear sensors, in linear light, half the possible values are wasted to encode 20% of the vision range. Sustainable if you have a lot more levels that the eyes can sees (16-bit or more), not sustainable if you barely have enough (8-bit).