Jellby wrote:

> Christopher James Huff wrote:
> 
> 
>>In article <3dac17d4$1@news.povray.org>,
>> "hughes, b." <omn### [at] charternet> wrote:
>>
>>
>>>I guess if negative lights were to do as expected of such a thing,
>>>though, then they'd actually illuminate shadows, or be a anti-shadow.
>>>
>>Why? Ordinary lights don't darken shadows, they just fail to illuminate
>>them.
>>
> 
> This brings Terry Pratchett to my mind. Normal darkness is just the absence 
> of light, but Discworld Darkness is negated light :D
> 
> OK, there are at least two ways of thinking about negative lights. If normal 
> lights lighten illuminated zones and don't affect shadows, negative lights 
> could:
> 
> 1.- Darken "illuminated" zones, don't touch shadows. (This is the most 
> logical approach)
> 2.- Lighten shadows, don't touch illuminated zones. (It has its logic too, 
> don't you think so?)
> 
> Is there a way to achieve the second way in POV-Ray? If there isn't (and if 
> there's any chance of implementing it someday), I suggest calling it 
> "inverted" light.
> 


You are thinking about 'positive' and 'negative' light source as the 
only way to touch the image.
You are forgetting 'Ambient' settings.

For:
  1. Do not touch ambient, add negative light
  2. add negative light and compensate the negative light with a raise 
of ambient light. It might be tricky if many textures have different 
ambient ratios.

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