Luster Categories 

When other value factors are equal, the higher the luster, the more valuable the pearl. There are five categories of luster:

Excellent—Reflections appear bright and sharp

Very Good—Reflections appear bright and near sharp

Good—Reflections are bright but not sharp

Fair—Reflections are weak and blurred

Poor—Reflections are dim and diffused

Eric Welch/GIA
Both of these strands have the same very good luster classification even though the Japanese saltwater cultured pearl strand at the bottom has slightly sharper reflections than the South Sea strand at the top. Japanese cultured pearls commonly have sharper reflections than South Sea cultured pearls.