Florian;
if the data is digitized or encoded in any way - then any description of it
must include the encodiing.
For example: log compresssion of sound/pressure values can be done in analog
electronics, but you still have to describe it as log encoded or you'll get
lousy results when you try to playback or process that signal later.
You really should use light as the baseline (truth) and reference the encoding
to that.
Saying that something is "perceptually linear" tends to confuse things.
Stating that human perception of light is approximately logarithmic is fine.
But describing an encoding (as you did) as "perceptually logarithmic" is quite
misleading (as I described previously).
Chris