luminosity is the amount of light,

In astronomy, luminosity is the amount of light, and other forms of radiant energy, a star radiates per unit of time. The luminosity of a star is determined by the radius and the surface temperature. However, many stars do not radiate a uniform flux—the amount of energy radiated per unit area—across their entire surface. The rapidly rotating star Vega, for example, has a higher energy flux at its poles than along its equator.^[110]

Surface patches with a lower temperature and luminosity than average are known as starspots. Small, dwarf stars such as the Sun generally have essentially featureless disks with only small starspots. Larger, giant stars have much bigger, much more obvious starspots,^[111] and they also exhibit strong stellar limb darkening. That is, the brightness decreases towards the edge of the stellar disk.^[112] Red dwarf flare stars such as UV Ceti may also possess prominent starspot features.[113