Luster measures pearl surface shininess (or mirror-like finish). The intensity of light reflection decides how high the luster is. Pearls have high luster when the reflections are bright and sharp. When the light reflections are weak and fuzzy, the pearls are dull. Thick nacre results in high luster.

Pearl luster is an important factor when determining a pearl's price. High lustrous cultured pearls are precious and they comand a high price in the market. Cultured pearls with dull or milky color have low luster and they are poor quality.

Akoya cultured pearls have a special luster that can't be found among other pearls. The special luster is caused by the temperature change of ocean water, where Akoya pearls are grown. Temperature changes in ocean water form aragonite crystals surrounding a pearl. These crystals are where the color and luster of Akoya pearls come from. Akoya, Tahitian, and South Sea pearls with significant amount of crystals are the most lustrous among all pearls.