Available Lights in CG Systems

Most current computer graphics systems use either scan-line rendering or ray tracing. This means that they treat the diffuse interreflections component of light as a constant and call it ambient light. Programs that render using the radiosity method compute this term and therefore produce much more realistic images. Aside from ambient light, most systems provide at least the following types of lights with the associated parameters (These are from Pixar Renderman):

A spotlight is more complex than the other light sources. The figure below shows the different parameters of the spotlight:

Similar to a pointlight, a spotlight has a position and a direction. The intensity falls off with angle such that the intensity = 1 in the direction of the spotlight (from--> to) and intensity = 0 at coneangle radians away. The fall off function F(ca) = F1 * F2, where F1= (L*A)^beamdistribution. A = from->to direction and L = light vector from surface point to spot light. So the larger the beamdistribution the faster the faster fall off. F2 = 1 from A to coneangle - conedeltaangle radians and has a smooth fall-off to 0 at coneangle radians. This is shown in the plots.

Here is a set of four images that illustrate these different types of light sources:

Ambient light only

Intensity = 0.5

ambient.gif (5052 bytes)
Distant light only

Intensity = 1.0

distant.gif (11437 bytes)
Point light only

Intensity = 30 and 6 units away

point.gif (10925 bytes)
Spot light only

Intensity = 30 and 6 units away

spot.gif (5386 bytes)

CG systems frequently have other types of lights, e.g. area lights that are not point light sources. Renderman does this by means of shaders (functions that are written in the Renderman shading language).

Lights in 3D Studio Max


Lighting in Computer Graphics
HyperGraph Home page.

Last changed November 02, 1998, G. Scott Owen, owen@siggraph.org