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Stellar luminosity determination at its most accurate and reliable (i.e., for some nearby stars) is carried out through stellar radius determination and stellar temperature determination and applying the relation they share. This is applicable in the special cases where the latter two can be very precisely determined. In other cases, if a reliable stellar distance determination is available, e.g., from parallax measurements, the distance's effect on the apparent magnitude can be accounted for and the absolute magnitude can be determined along with the bolometric magnitude which is generally equivalent to a luminosity measurement.
For main sequence stars at further distances, the spectral type provides a rough luminosity estimate. For a distant giant star, a radius based upon stellar models could be used, but this is likely even more uncertain. Spectral features associated with surface gravity provide clues regarding the star's radius. Other methods of stellar distance determination, which are generally rough, also yield rough luminosity estimates.