This is a spotlight shader.
INT  is the intensity of the light.
LGT  is the color of the light.
FROM is the position of the light.
TO   is where the light shines. 
FROM-TO is the direction vector for the light.
ANG  is half angle defining the size of the cone of light.
DLT  is the width of the falloff.
RATE is the rate of falloff.
ATT  is the attenuation distance.

This must be a float.  The default is 1.0.
This controls the intensity of the light.

This must be a color.  The default is WHITE.
This controls the color of the light.

This must be a point.  The default is 5 out in Z.
This is the position of the light. The vector defined by
TO-FROM is the direction vector for the light.

This must be a point.  The default is the ORIGIN.
This is where the light shines. The vector defined by
TO-FROM is the direction vector for the light.

This must be a float.  The default is 5.0.
This angle is half the size of the light cone.

This must be a float.  The default is 5.0.
This is the width of the falloff.
For best results this value should be less than ANG.

This must be a float.  The default is 1.0, linear falloff.
This is the rate of falloff within the width defined by DLT.
Larger numbers may cause antialiasing problems at the light's edge.

This must be a float.  The default is 1.0E6.
This is the distance from the light postion over
which the attenuation of the light takes place.

This is a spotlight shader.