Figure 10-10Luminosity Classes Dividing the H-R diagram into regions, called luminosity classes, permits finer distinctions between giants and supergiants. Luminosity classes Ia and Ib encompass the supergiants. Luminosity classes II, III, and IV indicate giants of different brightness. Luminosity class V indicates main-sequence stars. Because they do not create energy by fusion, like the other stars we have discussed so far, white dwarfs do not have their own luminosity class.