Blinn phong

[<ReflectedDefinition>]
    let surfaceColor (scene:SceneConstants) (mat:MaterialConstants) worldPos normal =

        let lightVec = scene.Light - worldPos 
        let lightDir = normalize lightVec
        let lightFallOff = 
            let lightVecSquared = (lightVec |> dot lightVec)
            scene.LightRangeSquared/lightVecSquared
            |> saturatef
        let diffuse = 
            normal 
            |> dot lightDir
            |> max 0.0f
            |> mul mat.Diffuse
            |> mul lightFallOff
            |> saturate
        let specular = 
            let viewer = scene.Eye - worldPos
                         |> normalize
            let half_vector = (lightDir + viewer)
                              |> normalize
            half_vector 
            |> dot normal
            |> max 0.0f
            |> pow mat.Shine
            |> mul mat.Specular
            |> mul lightFallOff
            |> saturate

        scene.AmbientLight + diffuse + specular
        |> saturate

You can find the full source code here