Tutorial on lights

Hi to all.
since I've finished my first tutorial (Andreas: it weighs 1 Mb due to all 
pictures; can send them to you for dispatching to the doc mainteners at 
KDE?), I'm now working on a new one named "Advanced Tutorial: a short study 
of lights". It deals, of course, with the different light system available. 
Point Light is already completed but Spot Lights gives me some difficulty 
with some parameters.

As I understood them, here are the definition I gave:

"Falloff: this value is equal to half the emitter's cone angle. The greater 
the value, the wider the beam and the surface lighted. Please note that this 
value must be lesser than or equal to 90. With a falloff of 90 degrees, the 
emitter behaves a surface emitter instead of a beamer.

Tightness: this value is a way to specify the fuzziness of the border of the 
lighted area. A low value indicates a very sharp border, while a high value 
indicates a very blurred border. The value is ranged from 0 to 90."

I am correct on these? And I failed to find a definition for Radius, even if I 
thought it as obvious at first hand...

I suppose povray has a documentation with all these parameters already 
defined. Is that true? Where can I find it?

--
Cheers,
Olivier Saraja
<http://www.linuxgraphic.org>
<http://www.blender-cafe.org>

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