Using synthesized and real spectra this article addresses questions regarding the degree to which synthetic and real sensor systems with one, two, and three sensors can distinguish among stimuli and can reconstruct the original spectra. Based on 64 synthetic spectra, the trichromatic sensors L, M, S distinguish the spectra at the level of 85% of the optimal result but reconstruct them only at the level of 70%. For symmetrical and symmetrically placed sensors the corresponding values are 76 and 94%. The conclusion is drawn that distinguishability was a more important goal of evolution than reconstructability. (C) 2005 Wiley Periodicals, Inc.