light intensity spot x1 y1 z1 x2 y2 z2 a [Qin Qout]
Place a spot light at (x1,y1,z1) shining towards (x2,y2,z2). Qin represents the angle (from the direction of the light) at which the intensity starts to decrease. Qout is the angle at which the intensity reaches zero. a controls the rate of the drop-off from Qin to Qout (the higher the number the faster the drop-off - see section 4.1 of The Rayshade User's Guide for details).
Figure 3-10
/*
spot.ray
Spot Light Example
Stephen Peter 18 Feb 93
*/
eyep 0 -24 0
lookp 0 0 0
screen 400 400
light 1 spot -5 -10 5 -5 0 5 -16 10 20
light 1 spot 5 -10 5 5 0 5 1 10 20
light 1 spot -5 -10 -5 -5 0 -5 16 10 20
light 1 spot 5 -10 -5 5 0 -5 64 10 20
surface wall
ambient 0.6 0.1 0.1
diffuse 0.9 0.8 0.6
box wall -12 0 -12 12 1 12
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THE END - Notes on Rayshade - 3 - Lighting and Atmospheric Effects - Spot Light