Reflection vs. Illumination

Light:

An electromagnetic energy flux that has

• intensity (power per unit area)
• direction of propagation

Reflection:

A local lighting model that relates

• the properties of a surface at a point
• the incoming direction and energy at the point
• the outgoing direction and energy at the point

BRDF:

bidirectional reflectance distribution function

• the function that embodies the surface properties

Illumination:

A global lighting model that computes

• overall light distribution in an environment
  • from the reflection models
  • from the shape and location of all objects
  • from the shape and location of all light sources

Shading:

A local interpolation technique used to

• reduce the cost of computing reflection
• shade polygons ``nicely''