The three classifications of sources of information are primary sources, secondary sources, and tertiary sources. Primary sources offer firsthand accounts or original data, secondary sources analyze and interpret primary sources, and tertiary sources provide summaries and overviews of information from primary and secondary sources.

Conventional sources are the same as conventional sources.

Irregular Sources and Regular Sources

Primary sources and secondary sources

The sources that can give out their own light are "Light Sources" and the same opposite the sources which can not give out their own light are know as Non Light Sources .