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When light passes through a surface either into or out of a dense medium
the path of the ray of light is bent. Such bending is called
refraction. The amount of bending or refracting of light depends upon
the density of the material. Air, water, crystal and diamonds all have
different densities and thus refract differently. The index of
refraction or ior value is used by scientists to describe the
relative density of substances. The ior keyword is used in
POV-Ray in the interior to turn on refraction and to specify the
ior value. For example:
object { MyObject pigment {Clear } interior { ior 1.5 } }
The default ior value of 1.0 will give no refraction. The index of refraction for air is 1.0, water is 1.33, glass is 1.5 and diamond is 2.4.
Normally transparent or semi-transparent surfaces in POV-Ray do not refract
light. Earlier versions of POV-Ray required you to use the
refraction keyword in the finish statement to turn on
refraction. This is no longer necessary. Any non-zero ior value
now turns refraction on.
In addition to turning refraction on or off, the old refraction
keyword was followed by a float value from 0.0 to 1.0. Values in between 0.0
and 1.0 would darken the refracted light in ways that do not correspond to
any physical property. Many POV-Ray scenes were created with intermediate
refraction values before this bug was discovered so the feature has been
maintained. A more appropriate way to reduce the brightness of refracted
light is to change the filter or
transmit value in the colors
specified in the pigment statement or to use the fade_power
and fade_distance keywords.
See "Attenuation".
Note: neither the ior nor refraction keywords cause the
object to be transparent. Transparency only occurs if there is a non-zero
filter or transmit value in the color.
The refraction and ior keywords were originally
specified in finish but are now properly specified in
interior. They are accepted in finish
for backward compatibility and generate a warning message.
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