If you like that article, I highly recommend sinking your teeth into
Now for the specular reflection (highlight). We see the highlight at the point on the sphere where the surface is at just the correct angle to bounce light from the light source to our eyes - that is, where the angle of incidence equals the angle of reflection. For spheres in general, this in NOT in the middle of the centre-light, but at a point on the line between the middle of the centre-light and the middle of the sphere as we see it. (Light hitting the middle of the centre-light hits the surface at right-angles, and so bounces straight back to the light source, not to our eyes).