From the documents ( and I quote):

The phong and specular highlighting models available in POV-Ray are
alright, but they are quite simplified models. A better model has been
developed over the years. This is the Torrance-Sparrow-Blinn-Cook
microfacet highlight model.
Blinn highlights (as they will be called) uses statistical methods to
simulate microfacets on the surface to produce the highlight. The model
uses the fresnel reflectivity equation, which determines reflectivity
from the IOR (index of refraction) of the material. For this reason, you
must use an interior with an IOR if you want to use blinn highlights.

As with phong and specular, the size blinn highlights can be adjusted.
To do this, use the facets keyword. The float value following this
keyword specifies the average (r.m.s.) slope of the microfacets. A low
value means shallow microfacets, which leads to small highlights. A high
value means high slope (very bumpy), which leads to large, soft
highlights.
Example:

sphere {
  0.0, 1 
  texture {
    pigment {radial frequency 8} 
    finish{ blinn 1 facets .2 }
  }
  interior {
    ior 20 // this is a guess for IOR
  }
}

Chris Huff wrote:
> 
> In article <38D523F6.CA1ED4D9@gci.net>, "mr.art" <mr.### [at] gcinet>
> wrote:
> 
> > don't forget that you need to specify an ior value
> > in interior {} before this will have an effect.
> 
> You don't need an ior value for blurred reflection to work. They are not
> related. The only time ior is used in reflections is for the fresnel
> function in angle-dependant reflection, which is activated by using
> "reflection_type 1" in the finish.
> 
> --
> Chris Huff
> e-mail: chr### [at] yahoocom
> Web page: http://chrishuff.dhs.org/

-- 
Mr. Art

"Often the appearance of reality is more important 
than the reality of the appearance."
Bill DeWitt 2000

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