Frederick Sumner Brackett (August 1, 1896 – January 28, 1988), was an American physicist and spectroscopist.
Born in Claremont, California, he graduated from Pomona College and worked as an observer at Mount Wilson Observatory until 1920. He observed the infra-red radiation of the Sun. Brackett received a doctorate in physics from the Johns Hopkins University in 1922. Applying a hydrogen filled discharge tube, he discovered the hydrogen Brackett series, where an electron jumps up from or drops down to the fourth fundamental level, in 1922. Before moving to the Washington area in 1927, he taught physics at the University of California, Berkeley. He joined the Department of Agriculture's Fixed Nitrogen Lab in 1927 and transferred to the National Institute of Health (NIH) in 1936 as director of biophysics research.
During World War II, he directed a research optics program at the Army. He was promoted to the rank of lieutenant colonel and received the Legion of Merit for his work.
Brackett returned to the NIH as chief of the photobiology section. He retired in 1961.
The lunar crater Brackett is named after him.