Attenuation

• We will model two types of lights:
  • Directional
  • Point
  Want to determine for each
• Directional light source has parallel rays:

  \

  Most appropriate for distant light sources (the sun)

  No attenuation.

Point light sources:

  

• Light emitted from a point equally in all directions:

  \

• Conservation of energy tells us

  

  where r is the distance from light to P

• In graphics, attenuation looks too harsh.

  Harshness due to approximation of ambient lighting.

  Commonly, we will use

  

• Note that we do NOT attenuate light from P to screen (even though Lambertian model suggests we should).

  \

  The pixel represents an area that increases as the square of the distance.