How can I model daylight effect of a light well under landscape pond?

edit

Here's a partial Radiance scene description for a swimming pool that uses the 'dielectric' primitive:

# pool.rad

void plastic white_paint
0
0
5 .5 .45 .4 0 0

# pool water
void texfunc wavy
6 wave_x wave_y wave_z wave.cal -s .25
0
1 .05

wavy dielectric wavy_water
0
0
5 .9 .9 .91 1.33 0

# wavy glass wavy_water
# 0
# 0
# 4 .9 .9 .91 1.33

# genbox white_paint pool 3 5 1

[etc...]

(source: http://radsite.lbl.gov/radiance/diges...)

This suggests that the RGB transmittance of water is ~90%, which is a good starting point. Next, you're modeling as "glass" instead of "water" (or in Radiance parlance: "dielectric"), so you need to add a factor for the water depth and turbidity, among other things. This is where it gets messy, but some interesting references I saw are this and that.

Good luck/have fun! - Rob