Point Light Sources

Point Light Sources:

• Point light sources have a position and an intensity
• Light energy is radiated equally in all directions

Distance Attenuation:

• Physically, need attenuation since light energy spreads out spherically.
• This is too harsh; point light sources are rare in the real world.
• Use modified attenuation factor:

  

• This simulates the attenuation of an area light source.
• Only use attenuation from light source to surface, not from surface to pixel.
• Pixel is area, not point, so foreshortening cancels attenuation.

Ambient Lighting:

• True global illumination difficult and expensive to calculate.
• Often use constant low level lighting everywhere to fake global illumination: .
• Each surface may reflect ``ambient'' lighting differently: .
• Usually, .

Lambertian Lighting:

at point x with point light sources at points is now:

Specular Lighting Similarly

For example

• Sometimes we see the Phong model stated with the half-vector :
  • 
  • Angle between n and h is twice that between r and v if coplanar
  • Use
  • Not exactly the equivalent of using reflection vector r
  • Avoids recomputation of v
• Better approximations can be made to surface materials if we allow multiple Phong lobes (SIGGRAPH 97)