Despite having a cooler surface, how does a red giant's total luminosity compare to its main sequence stage?

Answer

The total luminosity increases substantially due to massive size.

Although the surface is cooler per square meter, the star's enormous expansion means its sheer size results in a substantial overall increase in total energy output, or luminosity.

Despite having a cooler surface, how does a red giant's total luminosity compare to its main sequence stage?

#Videos

Why Do Red Giant Stars Get Bigger? - YouTube

astrophysicsred giantstar evolutionmain sequence star