1. The first thing to note for this situation is we will not be using visible light. we will be using only photons that are emitted from the light. Therefore the first thing we need to do is uncheck "Emit Diffuse" and "Emit Specular" in the light attributes. See figure 3.1

2. So that the light covers the area of the "waterSurface" Plane we need to increase the size of the "Cone Angle". if you have followed these instructions correctly you will need to change this value to "74". See figure 3.1

To confirm that this has worked you can select the light and in the viewport select "Panels > Look Through Selected". the circle that you see is the cone angle. See figure 3.2


figure 3.1


figure 3.2

3. Now is time to setup the photon emission. open up the attributes for the light again and open up the "Mental Ray" and scroll down to the "Caustic and Global Illumination" Section.

4. Check the box next to "Emit Photons" and you'll see the section light up. Now set the "Exponent to "1.5".
You'll notice that the "Caustic Photons" option is still greyed out. this is not a problem. we just haven't told maya that we want Caustics yet. See figure 3.3


Figure 3.3

5. Open up the Render Options Diologue box and make sure the renderer is set to "Mental Ray" then open up the tab "Indirect Lighting". Open up the "Caustics" Section and check the box next to "Caustics". See figure 3.4


figure 3.4

6. if you now close the attributes for the light and open them again the option for caustic photons will be available. Set this value to 500000. See figure 3.5


figure 3.5

Thats it for the light. in the next section we will be setting up the "parti_volume" node...