Units Home › Forums › Spectroscopy › Novae Cas and Per 2020 H alpha at medium resolution › Units 6 December 2020 at 9:05 am #583467 Dr Paul LeylandParticipant I used cm^-1 as an energy unit for a few years when doing my DPhil research. In those units red is about 15000, yellow about 20000 and violet about 25000.