Turtle program to change the caps on a light nexus to keep it powered almost all the time
Place a mining turtle on top of each of the four caps, put two blocks you want for the daytime (like diamond blocks) in the first inventory slot and two blocks into the second slot for nighttime (like moonstone) http://www.computercraft.info/forums2/index.php?/topic/20183-ars-magica-2-cap-replacer/