The law has been found to be immensely useful, but to fail for very faint and for very strong sensations. Within its useful range, Fechner's law is that sensation is a logarithmic function of physical intensity. S. S. Stevens pointed out that such a law does not account for the fact that perceived relationships among stimuli (e.g., papers coloured black, dark grey, grey, light grey, and white) are unchanged with changes in overall intensity (i.e., in the level of illumination of the papers). He proposed, in his famous 1961 paper entitled "To Honor Fechner and Repeal His Law", that intensity of stimulation is related to perception via a power-law.