Specular reflection obeys equal incidence and reflection angles locally on curved surfaces

Evidence

When you look in a mirror, you see light that has been specularly reflected, bouncing off the mirror according to the following rule: the angle of incidence equals the angle of reflection (figure 2.6). If the surface gently curves on a scale much bigger than the wavelength, the angle of incidence rule holds locally at each point along the surface. Initially, parallel rays fall at different places on the surface and are directed at various new angles relative to each other, as in a concave telescope mirror. — Eric J. Heller, Why You Hear What You Hear- An…, 164

Categorization

• ADDENDUM: Mirror geometry as worldbuilding-relevant infrastructure connects to trees-as-sound-barriers and acoustic surfaces themes.