Types of Light Source Ambient No position in space. Point Source At a point in space. Equal intensity in all directions. Directional Source Source is “at infinity.” Has direction only.

1. An Introduction to the Lighting
Model
Lecture 23
Wed, Oct 22, 2003

2. Types of Light Source
Ambient
 No position in space.
Point Source
 At a point in space.
 Equal intensity in all directions.
Directional Source
 Source is “at infinity.”
 Has direction only.

3. Calculation of Lighting
We will look at the details of how
lighting is calculated later.
For now, we just want to be familiar
with the kinds of lighting and how it
relates to a polygonal mesh.

4. Ambient Light
Ambient light illuminates objects equally
in all directions.
In real life, ambient light is light that
has been reflected off so many surfaces
that it is impossible to identify the
source.

5. Computing Ambient Reflection
The ambient reflection depends on
 The ambient light inherent in the scene.
 The ambient light given off by the light
sources.
 The ambient property of the surface.

6. Point and Directional Sources
At each point of a surface, the light has
a direction.
 Point source – direction varies with position
on surface.
 Directional source – direction does not vary
with position on surface.
With a point source, the intensity may
also depend on distance from the
source.

7. Computing Diffuse Reflection
Intensity of reflected light
 Depends on angle of incidence.
 Is equal in all directions, i.e., does not
depend on the viewing angle.
It can be computed more efficiently if
the light is directional, since there is
one less variable.

8. Specular Reflection
Intensity of reflected light varies with
viewing direction.
Maximum intensity is in the direction
pointing directly back to the light
source.

9. Specular Reflection
Specular reflection creates the
appearance of “shininess.”
Surfaces with a high specular reflection
appear very shiny.
Surfaces with a low specular reflection
appear matte.

10. Computing Specular Reflection
Computing specular reflection is less
efficient than computing diffuse
reflection, since it depends on the
direction to the light source and the
direction to the viewer.
The calculations can be speeded up if
the viewer is “at infinity.”

11. Emissive Lighting
Emissive lighting is light that emitted by
the surface itself.
It is used for objects that are meant to
glow.
It is independent of all light sources and
directions.

12. Lighting in OpenGL
Since the ambient, diffuse, and specular
reflections depend on light sources,
there is a separate contribution for each
light source.
Furthermore, there is a separate color
component for each type of light.
 Red, green, blue.

13. Finding the Shade of a Surface
The total reflection from a point, both
color and brightness, is the sum of the
ambient, diffuse, and specular
reflections and the emissive light.
This is a combination of properties that
are intrinsic to the surface and
properties that are intrinsic to the light
source.

14. Shading a Mesh
To shade a mesh, the program must
shade each polygon in the mesh
independently.
For large meshes (between 1 million
and 1 billion polygons), this can
consume a significant amount of time.
Animations are out the window.

15. Example: Lighting a Sphere
LightingDemo.cpp