- We will model two types of lights:
- Directional
- Point

- 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.

- Light emitted from a point equally in all directions:

CS488/688: Introduction to Interactive Computer Graphics

University of Waterloo

Computer Graphics Lab