The relationship between the luminosity of a star on the main sequence and its mass. Factors involved include whether radiation or convection is the dominant energy transport process, and, if the former, the type of opacity involved. For stars of less than 0.4 solar masses, which are fully convective, the luminosity varies as the square of the mass. For stars of mass similar to or slightly less than the Sun, the luminosity is approximately proportional to the mass to the fifth power (e.g. a star with twice the mass will have 32 times the luminosity). For more massive stars, the luminosity varies approximately as the mass cubed (e.g. a star with twice the mass will have about 8 times the luminosity).