Blinn–Phong Shading Model

Also called Blinn–Phong reflection model or modified Phong reflection model.  Trade visual precision for computing efficiency.

Default shading model used in OpenGL.

 

Differences (ref: wikipedia)

The halfway angle is smaller than the angle we want in Phong's model, but considering that Phong is using, we can set an exponent so that is closer to the former expression.

The size of the specular highlights can be matched in this way very closely to a corresponding Phong reflection, but they will always retain a subtly different shape.