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.

During World War I he served in France with the American Expeditionary Force, holding the rank of major of engineers.

• He was the eponym of the Lyman series of spectral lines.
• The crater Lyman on the far side of the Moon is named after him.
• He was elected to the American Academy of Arts and Sciences in 1901.^[1]
• He was elected to the United States National Academy of Sciences in 1917.^[2]
• He was elected to the American Philosophical Society in 1918.^[3]
• He was awarded the Franklin Institute's Elliott Cresson Medal in 1931.
• The Lyman Laboratory of Physics at Harvard University is named after him.

He became a hereditary member of the Military Order of the Loyal Legion of the United States in succession to his father, Lieutenant Colonel Theodore Lyman III.

• This article incorporates text from a publication now in the public domain: Gilman, D. C.; Peck, H. T.; Colby, F. M., eds. (1905). New International Encyclopedia (1st ed.). New York: Dodd, Mead. {{cite encyclopedia}}: Missing or empty |title= (help)
• USGS Gazetteer of Planetary Nomenclature Feature Information
• 1931 Frederic Ives Medal

• National Academy of Sciences Biographical Memoir