Guys, hate be the bearer of bad news , but the maximum expansion of freezing water is right at 32 (within a fraction) when the ice crystals first form.
How long, how cold and will it freeze is simply a function of the temperature that the water in the block actually reaches. Wind is a major factor.
We used to keep a couple of coke bottles filled with water around the marina in the fall, we always had the guys that would call during that first cold snap, usually about 6 on a Friday nihgt and beg us to winterize their boat.
That is a lot of money to gamble with, The light bulb is a good idea, but be careful where you put it. A fire would be worse.