Three reflection regimes.

• Specular (mirror-like) — angle of incidence equals angle of reflection. Energy bounces in one direction only.
  • Examples: calm water surface, polished metal, wet pavement, glass.
• Lambertian (perfectly diffuse) — energy reflects uniformly in all directions; brightness appears the same from every viewing angle.
  • Natural example: freshly fallen snow; matte dry sand; whitewashed walls. (No real surface is perfectly Lambertian — it’s an ideal.)
• Regular / real surfaces — somewhere between the two. Most natural surfaces are diffuse-dominated with a specular component; this is why sensor geometry (BRDF) matters for precise measurements.