> Hi, I try to put a light source in the back of a LEGO creation with transparent
> pieces to create backlight pass through its pieces.You have a setting of light
> that could accomplish this?
>
>

Any normal light will work.
The backside illumination only work for single surfaces. So, you need a 
workaround:
 From fastest to slowest.

1) You can add interior_texture with  pigment{rgbt 1}. That way, the 
visible surface "see" right through the other surface.
2) You can use radiosity with at least 2 bounces. If you have any 
interior structures, you'll probably need recursion_limit 4 or more, and 
it get real slow.
3) You can use the new SSLT mechanism where you define a translucency 
for your material along with an ior around 1.5. When the translucency 
value become larger than the thickness of the object, you start to see 
whatever is behind the object. In the global_settings section, set 
mm_per_unit according to the scene scale. The default (10) is for a 
scene where 1 unit = 1 cm = 10 mm. Set to about 25 for a scene in inches.



For the transparent pieces, you need an interior block defining:
fade_colour
fade_distance
fade_power 1 or fade_power 1001
ior 1.5 (or close to that)
optionaly, some scattering or absorbing media matching the colour of the 
blocks.

The pigment for those should be something like rgbf 0.95 or rgbt 0.95 as 
the colour comes from the material itself and not the surface.



Alain

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