Ideal specular reflection is like a perfect mirror. I'm looking at the code to [SmallPt](http://www.kevinbeason.com/smallpt/) and see that one of the spheres has an ideal specular material:

```
Sphere spheres[] = {//Scene: radius, position, emission, color, material 
   / ...
   Sphere(16.5,Vec(27,16.5,47),       Vec(),Vec(1,1,1)*.999, SPEC),//Mirr
   / ...
 };

```

In the radiance calculation, this happens:

```
  } else if (obj.refl == SPEC)            // Ideal SPECULAR reflection 
     return obj.e + f.mult(radiance(Ray(x,r.d-n*2*n.dot(r.d)),depth,Xi)); 

```

where `f` is the object colour of `Vec(.999,.999,.999)`.

I was surprised to see colour multiplication here. Doesn't an ideal mirror have no colour? I guess as `f` is `Vec(.999,.999,.999)`, effectively it's passing through the colour almost unchanged? Any thoughts on why .999 was used and not 1? I'm guessing this is something to do modelling a miniscule energy loss?