The mass-luminosity relation is an equation relating a star's mass with its luminosity.
L M ————— = ( ————— )a LSun MSun
a = 3.5 is often used for main sequence stars. Stars close to the Eddington luminosity have a close to 1. a depends upon whether the star is the right size for significant convection.
Eclipsing binaries and parallax measurements help confirm the relation.