sun light

From Programming with DX9: A Shader Approach by Frank Luna, chapter 10 section 2:

"A directional light, or parallel light, approximates a light source that is very far away. Consequently, we can approximate all incoming light rays as parallel to each other. The common example of a real directional light source is the sun..."

He goes on to present calculating normals and demonstrates a vertex shader. Phong shading is covered in section 10, and the lighting calculations are easily moved to the pixel shader.