# Trouble using diffuse function

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Jennifer on 11 Mar 2024
Commented: Jennifer on 11 Mar 2024
Hello, I'm trying to use the diffuse() function to simulate Lamburtian reflectance off a surface and the help page leaves a bit to be desired. I'm having several errors running the function and was just hoping someone could provide me with an example use of the function so that I can confirm the syntax I'm using is correct.
My end goal is to calculate the reflected light off the surface and compare it to the light that continues past the target and reflects off a second surface. Any help would be greatly appreciated.

Florian Bidaud on 11 Mar 2024
Edited: Florian Bidaud on 11 Mar 2024
The structure is:
R = diffuse(Nx,Ny,Nz,S)
The output R is defined with Lambert's Law by R = cos(psi) where psi is the angle between the surface normal and light source.
If you have a surface on the (x,y) plan, the normal vector is [Nx,Ny,Nz] = [0,0,1].
S = [Theta Phi] is the direction vector of the light source in spherical coordinates (in degrees).
For example
S = [10 45];
R = diffuse(0,0,1,S)
R = 0.7071
You can also define S in the (x,y,z) coordinates. That would give, to have the same output:
S = [sind(45)*cosd(10) sind(45)*sind(10) cosd(45)];
R = diffuse(0,0,1,S)
R = 0.7071
Jennifer on 11 Mar 2024
Thank you for responding so quickly, my issue was in the S direction syntax. Also thank you for posting an example. My code works now. :)

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