Thanks again.
And (excuse my ignorance) about the radiosity?
I must include it for a good simulation?

Ehm...have you a sample scene that I can study?
I'm new to pov 3.5, and I only know roughly the old version...

thx,

          Manuel



"Matti Karnaattu" <nomail@nomail> ha scritto nel messaggio
news:web.3ec248f5a14066c9bef0bd7d0@news.povray.org...
> >I mean the simulation with the radiometry (or photometric) value of
> >a lamp (power, light intensity, or Photometric Solid, etc...).
>
>
> Best way to use POV-Ray light simulation is to multiply light source color
> with real light luminance (cm/m^2). Then set fade_distance using following
> formula:
>
>   sqrt(pi * A) / pi
>
> Real world fade_power is 2. Because POV-Ray doesn't have dynamic range
> compression, this isn't enough. I recommend you to define two adjusting
> variables "Gamma" and "Max_Luminance" to make dynamic range compression.
> Gamma is the gamma used to compress image dynamic range and Max_Luminance
> is the luminance (cd/m^2) where pixel luminance at range 0..1 is "1".
> Max_Luminance controls image brightness. When using these variables you
can
> calculate light source color multiplier using formula:
>
>   pow(light_source_luminance / Max_Luminance, Gamma)
>
> And global Fade_Power to *all* light sources by using formula:
>
>   (ln(-exp(-ln(2) * Gamma) + 2) + ln(2) * Gamma) * 2 / ln(3)
>
> To simulate photograph dynamic range compression I think that Gamma should
> be ln(0.5)/ln(0.18) because gray card which reflects 18% of light looks
> half bright.
> Light source color luminance (without multiplier) must be one. Good
starting
> value for Max_Luminance is 50. Light source colours luminances without
> multiplier must be one. Example for white light, light color is <1, 1, 1>.
>
> Because you probably want to make other light sources than
omnidircetional,
> you need to simulate light distribution using spotlights. If light source
> is flat, use spotlight radius -90 falloff 90 tightness 1 for cosine
> falloff.
>
> I don't recommend to use Jaime's lightsys because it doesn't use
physically
> accurate lightning. (Sorry Jaime).
>
> Matti
>

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