Which term describes the appearance of a material's surface in reflected light?

• A. Luster
• B. Luminescence
• C. Brightness
• D. Dispersion

Answer: (A)

Luster describes how a surface looks in reflected light—the quality of the surface sheen you see when light bounces off the material. It’s about the surface’s interaction with light, largely influenced by smoothness and the way light is reflected, not about how much light is emitted or how it splits into colors. That’s why it’s the best term for the appearance of a surface in reflection: it captures the characteristic shine you observe, whether glossy, metallic, pearly, or dull.

Luminescence would mean the material glows on its own, emitting light rather than simply reflecting it. Brightness refers to the overall amount of light perceived, which can change with lighting conditions and isn’t describing the quality of the surface’s reflection. Dispersion is the splitting of light into colors (like a rainbow) due to refraction, not the surface’s reflected appearance. In practice, diamonds can have a brilliant or adamantine luster, metals have a metallic luster, and pearls have a soft, nacreous luster, illustrating how luster characterizes surface reflection across different materials.