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In order to compute a first test spectrum, go to the main window and set the simulation parameters as shown below (Click the Parameters button to open this dialog):

Then press the Simulation button to start the ray-tracing work. After a while you can inspect the result: Open the list of objects and there the detector object. Display the spectrum with View data (Eventually the graphics settings must be modified):

Note that the volume fraction of 0.1 for the glass spheres is not very realistic since they are not embedded in a solid host material. Go to the list of scatterers, open the 'Glass spheres' and set the volume fraction to a more realistic value of 0.5 . Use the Update command to recompute the scattering and absorption coefficients:

Now do the simulation again. The result

is not very different from the case above. This is due to the fact that almost no ray reaches the side walls in both cases, and what you see is a 'halfspace spectrum' of scattering glass spheres in both cases.
Not in reality, but in the model we can set the glass sphere volume fraction to much lower values, for example to 0.001, and recompute the diffuse reflectance spectrum:

Now the spectrum is dominated by the large regular reflection of radiation by the metal on the bottom of the cup. The diluted glass spheres absorb significantly below 2000 1/cm only.
It's a good exercise for you to place some screens and detectors in the system to investigate where is how much radiation. Especially in the 'dense' system with a volume fraction of 0.5 it might be of interest to find out how deep the radiation penetrates the scattering system, or how far from the incident beam the light comes out again.

To finish this tutorial we now compute the diffuse reflectance spectrum for the water coated glass spheres. Open the list of interfaces and the list of scatterers. Open the scatterers called 'Glass spheres' and there the parameters window. Assign the layer stack 'Air-water-glass' to the sphere coating, and use the filename mie2 for the transfer and output files. Then close the parameters window and use the command Calc Mie data and wait to recompute the scattering and absorption characteristics. Set the volume fraction back to 0.5 and do the ray-tracing simulation again. The detector signal (which is the diffuse reflectance of the sample) is much lower now due to water absorption:

This configuration can be found in tu1_ex2_4.s99.

Serious results should be obtained with a much lower noise level, of course. In order to show the difference I have computed the spectrum above again, now with 10000 rays per spectral point instead of 100. Here is the result: