(difference between an object's bolometric and visual magnitudes)
Bolometric correction is a difference between a star's
visual magnitude and bolometric magnitude;
when the former is determined, the bolometric correction
can be used to determine the latter.
It varies by type of star, e.g., spectral type, and is
largest for stars much hotter or cooler than the Sun because
the EMR from stars of the Sun's temperature
is centered around visible light.
Some examples of bolometric correction determinations: