Ambient, diffuse and specular light

Ambient light

Ambient light is the uniform background light that comes from reflections off all surrounding objects. It lights every surface equally from all directions and has no direction.

I_amb = ka · Ia

(ka = ambient reflection coefficient, 0 to 1; Ia = intensity of ambient light.)

Diffuse reflection

Diffuse reflection is the scattering of light equally in all directions from a rough, dull surface. Its brightness does not depend on the viewing position, but on the angle θ between the surface normal N and the light direction L (Lambert's cosine law).

I_diff = kd · IL · cosθ = kd · IL · (N · L)

(kd = diffuse coefficient, IL = light source intensity.)

Specular reflection

Specular reflection is the mirror-like reflection from a shiny surface that gives a highlight. It is strongest in the direction R of ideal reflection and depends on the angle φ between R and the viewing direction V.

I_spec = ks · IL · cos^n φ = ks · IL · (R · V)^n

(ks = specular coefficient, n = shininess exponent, R = 2(N·L)N − L.)

Total (Phong) model

I = ka·Ia + kd·IL·(N·L) + ks·IL·(R·V)^n