I've commented all the changes I've made, the only problem with using plains is the need for the fourth parameter to be 1 which fixes some texturing issues.
rem set sync on
sync on
sync rate 0
lm start
make object sphere 1, 10
position object 1, 0,20,0
rem must add the extra parameter to the MAKE OBJECT PLAIN command to make texturing work
make object plain 2, 80,80,1
position object 2, 0,0,0
xrotate object 2, 90
rem need to use negative values on the Y axis to point downwards
rem colour is a float value between 0,0,0 for black and 1,1,1 for white
lm add spot light 0,70,15, 0,-20,0, 45,90, 500, 1,1,1
LM Add Collision Object 1
LM Add Collision Object 2
LM Build collision Data
LM Add Light Map Object 1
LM Add Light Map Object 2
make camera 1
position camera 1, 40,10,40
point camera 1, 0,0,0
rem need to use a larger texture size and higher quality
lm build light maps 256, 3.0, 1
do
rem just some controls to zoom in/out
if upkey()=1 then move camera 1,0.01
if downkey()=1 then move camera 1,-0.01
sync
loop
