  Methods of obtaining stellar luminosities (L) have been revised and a new
concept, standard stellar luminosity, has been defined. Among the three methods
(direct method from radii and effective temperatures, method using a
mass-luminosity relation (MLR), and method requiring a bolometric correction),
the third method, which uses the unique bolometric correction (BC) of a star
extracted from a flux ratio ($f_{\rm V}/f_{\rm Bol}$) obtained from the
observed spectrum with sufficient spectral coverage and resolution, is
estimated to provide an uncertainty ($\Delta L/L$) typically at a low
percentage, which could be as accurate as 1% perhaps more. The typical and
limiting uncertainties of the predicted L of the three methods were compared.
The secondary methods requiring either a pre-determined non-unique BC or MLR
were found to provide less accurate luminosities than the direct method, which
could provide stellar luminosities with a typical accuracy of 8.2% - 12.2%
while its estimated limiting accuracy is 2.5%.
