[Therion] loch light

i think it would be useful to let he user turn on the light in loch. the attached example is a loch model with dem and a geological map. the screenshot has been reduced 2x2, and the map is a very approximate drawing (a quick test to see if i could get something interesting). nevertheless it is nice to see the formations where the caves are ... and the potential for more caves that lies down there. without light the image is "flat". marco