The Phong reflection model works quite well, but has some drawbacks. A slight change to the model, introduced by James Blinn, is more commonly used in practice. The Blinn-Phong model replaces the vector of pure reflection with the so-called halfway vector, and produces specular highlights that have been shown to be more realistic. This model is discussed in The Blinn-Phong reflection model recipe in Chapter 4, Lighting and Shading.