Hi Avijit,
Well, if you have no data, you'll just have to make up something as best you can. First make the walls a MIRROR material, so that light reflects from it, and then use a coating to give it the reflectivity you want. I'd suggest an IDEAL coating with say 98% reflectivity (and hence 2% loss), obviously do better if you can. A TABLE coating is a simple way to add a wavelength-selective response if you have the data.
Then there is the scattering. If the surface has a glossy finish, make say 80% of the light reflect and 20% scatter into a Lambertial distribution. If it's a matte finish I'd go for 50/50 specular/diffuse or maybe 20/80. Again, get as much data as you can and just use my numbers as best-guesses.
The save the profile as day 'White Surface' so that if you do get better data later on, you only have to update one thing and all surfaces with this finish will automatically update :-)
There's a good KB article here:https://my.zemax.com/en-US/Knowledge-Base/kb-article/?ka=KA-01353
- Mark