NOT ONLY do these light up their direct surroundings very effectively, they ALSO cast a huge ray of light into the sky. The downside is they are very expensive. Sea lamp. read more
This means that if a torch (level 14) is placed on the floor, the light level on the adjacent floor blocks in all four direction will be 13 while the diagonal blocks in all four directions will have light level 12 (e.g. 14 minus 1 south, minus 1 east). read more