Weber-Fechner law

noun

We·​ber-Fech·​ner law ˈweb-ər-ˈfek-nər-  ˈvā-bər-ˈfeḵ-nər- 

: an approximately accurate generalization in psychology: the intensity of a sensation is proportional to the logarithm of the intensity of the stimulus causing it

called also Fechner's law