Free-running and light-induced circadian activity rhythms of wolf spiders will be measured using digital circuitry and punched paper tapes for computer analysis. The point will be to determine intensities of a number of different wavelengths of light which will have the same phase-shifting effect upon free-running (dark) activity, that is, which will appear equally bright. Such intensities will allow determination of behavioral spectral sensitivities for comparison with electrophysiologically measured spectral sensitivities of these animals' eyes.