Note that specular and Phong highlights are not mutually exclusive. It is possible to specify both and they will both take effect. Normally, however, you will only specify one or the other.
The Phong method measures the average of the facets facing in the mirror direction from the light sources to the viewer.
Phong's value is typically from 0.0 to 1.0, where 1.0 causes complete saturation to the light source's color at the brightest area (center) of the highlight. The default phong 0.0 gives no highlight.
The size of the highlight spot is defined by the phong_size value. The larger the phong size the tighter, or smaller, the highlight and the shinier the appearance. The smaller the phong size the looser, or larger, the highlight and the less glossy the appearance.
Typical values range from 1.0 (very dull) to 250 (highly polished) though any values may be used. Default phong size is 40 (plastic) if phong_size is not specified. For example:
If phong is not specified phong_size has no effect.
The specular value is typically from 0.0 to 1.0, where 1.0 causes complete saturation to the light source's color at the brightest area (center) of the highlight. The default specular 0.0 gives no highlight.
The size of the spot is defined by the value given for roughness. Typical values range from 1.0 (very rough - large highlight) to 0.0005 (very smooth - small highlight). The default value, if roughness is not specified, is 0.05 (plastic).
It is possible to specify wrong values for roughness that will generate an error when you try to render the file. Don't use 0 and if you get errors check to see if you are using a very, very small roughness value that may be causing the error. For example:
If specular is not specified roughness has no effect.
White light reflected specularly from a metallic surface takes the color of the surface, except then the incidence angle approaches 90 degrees, where it becomes white again.
The metallic keyword may be follow by a numeric value to specify the influence the above effect has (the default value is one). For example:
If phong or specular is not specified metallic has no effect.
This gives the object a mirrored finish. It will reflect all other elements in the scene. Usually a single float value is specified after the keyword even though the syntax calls for a color. For example a float value of 0.3 gets promoted to the full color vector < 0.3,0.3,0.3,0.3,0.3> which is acceptable because only the red, green and blue parts are used.
The value can range from 0.0 to 1.0. By default there is no reflection.
Adding reflection to a texture makes it take longer to render because an additional ray must be traced. The reflected light may be tinted by specifying a color rather than a float. For example
gives a real red mirror that only reflects red light.
Note that although such reflection is called specular it is not controlled by the specular keyword. That keyword controls a specular highlight.
Note that it is recommended that you only use refraction 0 or refraction 1 (or even better refraction off and refraction on). Values in between will 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. Note also that refraction does not cause the object to be transparent. Transparency only occurs if there is a non-zero filter or transmit value in the color.
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 to specify the value. For example:
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. The file consts.inc pre-defines several useful values for ior.
Note that if a texture has a filter component and no value for refraction and ior are supplied the renderer will simply transmit the ray through the surface with no bending. In layered textures, the refraction and ior keywords must be in the last texture, otherwise they will not take effect.
The fade_distance keyword determines the distance the light has to travel to reach half intensity while the fade_power keyword describes how fast the light will fall off. For realistic effects a fade power of 1 to 2 should be used.
The attenuation is calculated by a formula similar to that used for light source attenuation.
Since it is a very difficult and time-consuming process to actually calculate those effects (though it is not impossible) POV-Ray uses a quite simple method to simulate caustics caused by refraction. This caustic effect is limited to areas that are shaded by the translucent object. You'll get no caustic effects from reflective surfaces nor in parts that are not shaded by the object.
The syntax is:
Section 7.6.3.3.2
Specular Highlight
Section 7.6.3.3.3
Metallic Highlight Modifier
Section 7.6.3.4
Specular Reflection
Section 7.6.3.5
Refraction
Section 7.6.3.5.1
Light Attenuation
1
attenuation = --------------------------------------
1 + (d / FADE_DISTANCE) ^ FADE_POWER
Section 7.6.3.5.2
Faked Caustics
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