Lamberts Cosine Law - Diffuse Reflection
"LAMBERTS COSINE LAW" specify that the radiant energy from any minute surface area dA in any direction θ relative to the surface usual is proportional to Cos θ.
In condition of diffused reflection the source is directional although reflection is uniform. As, Id → Intensity of incident as diffused light
After that as per the Lambert's law the intensity of reflected light (I) will be a cos θ. Here, θ = Angle among unit direction of incident light vector and unit standard to the surface as or angle of incidence.
I a cos θ ⇒ less θ leads to more reflection and more θ leads to less reflection
Dot product of N and L vectors
cos θ = cos θ (∴Q | N¯ | and | L¯ | are)