Raman's second important discovery on the scattering of light was a new type of radiation, an eponymous phenomenon called the Raman effect. After discovering the nature of light scattering that caused blue colour of water, he focused on the principle behind the phenomenon. His experiments in 1923 showed the possibility of other light rays formed in addition to incident ray when sunlight was filtered through a violet glass in certain liquids and solids. Ramanathan believed that this was a case of a "trace of fluorescence." In 1925, K. S. Krishnan, a new Research Associate, noted the theoretical background for the existence of an additional scattering line beside the usual polarised elastic scattering when light scatters through liquid. He referred to the phenomenon as "feeble fluorescence." But the theoretical attempts to justify the phenomenon were quite futile for the next two years.
The major impetus was the discovery of Compton effect. Arthur Compton at Washington University in St. Louis had found evidence in 1923 that electromagnetic waves can also be described as particles. By 1927, the phenomenon was widely accepted by scientists, including Raman. As the news of Comptons Nobel Prize in Physics was announced in December 1927, Raman ecstatically told Krishnan, saying:But the origin of the inspiration went further. As Compton later recollected "that it was probably the Toronto debate that led him to discover the Raman effect two years later." The Toronto debate was about the discussion on the existence of light quantum at the British Association for the Advancement of Science meeting held at Toronto in 1924. There Compton presented his experimental findings, which William Duane of Harvard University argued with his own with evidence that light was a wave. Raman took Duanes side and said, "Compton, youre a very good debater, but the truth isnt in you."