Lyman became an assistant professor in physics at Harvard, where he remained, becoming full professor in 1917, and where he was also director of the Jefferson Physical Laboratory (1908–17). He made important studies in phenomena connected with diffraction gratings, on the wavelengths of vacuum ultraviolet light discovered by Victor Schumann and also on the properties of light of extremely short wavelength, on all of which he contributed valuable papers to the literature of physics in the proceedings of scientific societies.