three kind of light:
ambient
diffuse:
Ie Kd (N•L)
le:power of light
kd:coefficient of diffuse
N:norm of the vector
L:vector from vector to light
it should be Ie Kd cos(theta), theta is the angle between N and L, but when N and L are normalized, it can be cos(theta)=N*L.
specular:
Ie Ks(R•E)^s
R:vector of the reflection of L,R = 2 * dot(N,L) * N – L
E:vector from vector to eye
s:specular index, the spot is more clear when s is higher
shshwdr 