By Trey
Here it is:
* | 10 square feet or one room. |
** | 50 square feet or a house or a single story in a building. |
*** | 75 square feet or a large building. |
**** | 100 square feet. |
***** | 500 square feet. |
These are just guidelines; feel free to change them. I would also add that the light source has no "heat" or temperature and can be cast on an object (a statue, torch, door, etc.). If it's cast on a person (say your enemy's eyes) then I would call for a resistence roll or something.