The Phong reflection model is a simplification of the more general rendering equation, which takes advantage of the following simplifications when deciding the shade of a pixel during rasterization of a surface:

- It is a
*local*reflection model, i.e. it doesn't account for second-order reflections, as do raytracing or radiosity. In order to compensate for some of the losses of light, an extra*ambient lighting*term is added to the scene that is rendered. - It divides the reflection from a surface into two subcomponents,
*specular*reflection and*diffuse*reflection.

If we then define, for each *material* (which is typically assigned 1 to 1 for the objects in the scene, so that it is a sphere of material 1, which is a material which looks like e.g. copper, a cone of material 2, which is a material which looks like brass etc:

- specular reflection constant, the ratio of reflection of the specular term of incoming light
- diffuse reflection constant, the ratio of reflection of the diffuse term of incoming light
- ambient reflection constant, the ratio of reflection of the ambient term present in all points in the scene rendered
- is a
*shininess*constant for this material, which decides how "evenly" light is reflected from a shiny spot

Then the shade value for each pixel can be calculated using this equation, which is the *Phong shading equation*:

(When we have color representations as RGB values, this equation will typically calculated individually for R, G and B intensities, which are then concatenated and written to the video frame buffer memory simultaneously.)