When Hydrogen gas is passed through a discharge tube (A hydrogen discharge tube is a slim tube containing hydrogen gas at low pressure with an electrode at each end) and If a high potential is applied across this (as high as 5000 volts), the tube glows with a bright pink light. When this light or radiation is allowed to pass through a prism, it was observed to split into its various colors. The observed spectrum is just a small part of the hydrogen emission spectrum. The maximum part of the spectrum is invisible to the eye because it falls in the infra-red or ultraviolet range.
Here what happened actually is – the hydrogen atoms of the molecule dissociated as soon as an electric discharge was passed through a gaseous hydrogen molecule which resulted in the emission of electromagnetic radiation initiated by the energetically excited hydrogen atoms, called hydrogen emission spectrum or simply hydrogen spectrum which comprises radiation of discrete frequencies. These series of radiation are named after the scientists who discovered them.